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DrNomis_44
20-11-2015, 11:03 AM
Hi Everyone, I thought I would start a thread about a Valve Guitar Amplifier Head I've been working on since I was working as an apprentice Fitter and Machinist in my Dad's workshop back in 1997 (it was a 3-year apprenticeship) before I moved from Kununurra to Darwin in 2000, anyway, the Amplifier itself started out as a Mesa/Boogie Mk I and Marshall Super Lead 50 Hybrid, the preamp was the Mk I circuit and the power amp was the typical 50 Watt Marshall power amp design, but I could never get it to sound good in both the clean or overdriven modes, I could get the clean sound to have a good tone but the overdrive sound always lacked tonality no matter how I set the tone controls, it turned out to be due to where Mesa/Boogie put the tone controls in the preamp circuit.


I decided to rebuild the amp so that it was like a Soldano SLO 100, I've had to shelve the project for a while so I could put my money towards other things, but decided to post a pic of the amp in it's current state just in case you're interested in checking it out, here's a pic of the amp "as is":6634

wokkaboy
20-11-2015, 11:12 AM
nice one Doc, you must have a fair bit of knowledge to attempt mods to an amp head.
If you have any queries you could always ask Lozza (Lawry) has a very good knowledge of amps circuitry.

DrNomis_44
20-11-2015, 11:22 AM
nice one Doc, you must have a fair bit of knowledge to attempt mods to an amp head.
If you have any queries you could always ask Lozza (Lawry) has a very good knowledge of amps circuitry.


It's actually not a mod, it's a complete scratch build, I made the chassis myself from a piece of 2mm thick sheet Aluminium which I marked out and then cut off the excess material with a jigsaw with metal cutting blades, I got a local Kununurra Engineering company to Mig-Weld each of the corners for me after they bent the metal up in their metal-bending machine, the wooden cabinet was made from half-inch plywood covered in green pool table felt I bought from an upholsterer, the clear front panel is just some clear Perspex, I made the power transformer from a power transformer I salvaged from an old movie projector if my memory serves me right.


Cheers for that, I'll definitely have a yarn to Lozza when I get the chance to mate.

wokkaboy
20-11-2015, 11:25 AM
good stuff Doc, you must have learnt alot putting the amp head together. I wouldn't know where to start and would end up electrocuting myself !

DrNomis_44
20-11-2015, 11:30 AM
good stuff Doc, you must have learnt alot putting the amp head together. I wouldn't know where to start and would end up electrocuting myself !


I think I did learn alot as I went along, most of it was just doing alot of internet surfing for Amp schematics, checking out websites and trying lots of different circuits and stuff, I also learnt alot about electrical safety in the process too, if you follow some simple safety procedures amp building can be relatively safe as long as you know what you're doing.


I've been looking for a good Australian supplier of Guitar Amp-building components and materials for a while, one that I can order stuff from online relatively easily.


Here's a pic of the underside of the Amp's chassis:6635

wokkaboy
20-11-2015, 12:19 PM
well done Doc I am impressed. That's a big step to learn as you go build an amp head. Think I'll start building FX pedals and working up to an amp head !

DrNomis_44
20-11-2015, 12:25 PM
well done Doc I am impressed. That's a big step to learn as you go build an amp head. Think I'll start building FX pedals and working up to an amp head !


I'll be happy to give you some pointers about building FX pedals if you like mate.


If you're after a good diy valve overdrive pedal, I know one guy who lives in Christchurch New Zealand who sells a set of professionally etched circuit boards to build a pedal he designed called the Baja Real Tube Overdrive, I bought a set of the PCBs and built one, it worked first time, it runs off a 16V AC plugpack and uses a real 12AX7 valve, here's a link to the thread he started on the Freestompboxes.org forum of which I'm a member of:


http://freestompboxes.org/viewtopic.php?f=13&t=1790&sid=11131a30b3cf0e258a38b21e1f1f5e6c

wokkaboy
20-11-2015, 12:31 PM
thanks Doc, when I get my guitar hanging rack a bit lower I might ask for some tips

DrNomis_44
20-11-2015, 12:35 PM
thanks Doc, when I get my guitar hanging rack a bit lower I might ask for some tips


No worries at all mate.

stan
20-11-2015, 02:22 PM
nice work Doc. hopefully you will get it going how you want. Another vote for Lozza, he knows his stuff...

those valve OD pedals sound awesome, does he have a site or direct contact?

DrNomis_44
20-11-2015, 02:52 PM
nice work Doc. hopefully you will get it going how you want. Another vote for Lozza, he knows his stuff...

those valve OD pedals sound awesome, does he have a site or direct contact?



If you register yourself as a member of Freestompboxes.org (membership is free) you can PM the guy directly (exactly how I got in contact with him) and he will let you know the best way to order the PCBs from him, his username is bajaman, he's a really nice bloke to deal with.


He runs an electronics repair service in Christchurch in New Zealand, called Baja Electronics.

stan
20-11-2015, 04:54 PM
If you register yourself as a member of Freestompboxes.org (membership is free) you can PM the guy directly (exactly how I got in contact with him) and he will let you know the best way to order the PCBs from him, his username is bajaman, he's a really nice bloke to deal with.


He runs an electronics repair service in Christchurch called Baja Electronics.

great thanks

DrNomis_44
20-11-2015, 06:35 PM
great thanks


No worries, if you end up building one and you have trouble getting it to work, let me know.

lawry
24-11-2015, 05:55 PM
Ooooh. Valves! This will be a cool build. Especially if your going to go down the Soldano line. What sort of power/wattage are you thinking of?

DrNomis_44
24-11-2015, 07:19 PM
Ooooh. Valves! This will be a cool build. Especially if your going to go down the Soldano line. What sort of power/wattage are you thinking of?


Well, since the existing Output Transformer is only rated for 50 Watts and is for a pair of EL34 valves, I'm going to make the amp as a 50 Watter, one thing I do need to do is buy a proper Power Transformer for it because I made the existing one from a Power Transformer I salvaged from an old Reel To Reel Tape recorder, I removed all the Iron Core laminations, all the original windings, did some maths and then re-wound the primary and secondary windings according to the figures I came up with, it does work but generating the -V Bias supply is a bit of a headache, so I'd rather replace it with a proper Transformer.


Another thing I need to do is re-do all the front panel labeling as the all alignment is a bit sloppy, once that's done I'll clear coat the front panel.


I'm also going to be using Turret Boards to mount all the components on, so I need to find an online Australian supplier of Turrets, Turret Staking tools, and Turret Board Material.

WeirdBits
24-11-2015, 07:55 PM
Maybe try Evatco (http://www.evatco.com.au/product-category/tagboards-tagstrips-turrets/).

DrNomis_44
24-11-2015, 08:06 PM
Maybe try Evatco (http://www.evatco.com.au/product-category/tagboards-tagstrips-turrets/).


Cheers, will do.


Just had a look at the Evatco website, looks like just what I was after, I'll see if I'm able to order stuff from them online, cheers mate.

DrNomis_44
25-11-2015, 02:56 AM
Here's a dropbox link if you want to have a look at the SLO100 Schematic I'm going to be using to wire up my Valve Amp Head:


https://dl.dropboxusercontent.com/u/7787692/SLOCLONE-OFFICIAL-SCHEM18.pdf

DrNomis_44
28-11-2015, 08:01 PM
Update:


I've managed to make some progress on my Valve Amp Head, I looked through all the Transformers that Evatco have in stock and it looks like they can supply me with the right Power Transformer, they can also supply me with the Choke too, not only that, they can supply everything else I need too, I just had a quick look on the Internet for a suitable Turret Board layout and managed to find a set of three that should do the job, I'm going to leave buying all the bits I need till next year and will start working on the amp once I have everything, I'm also thinking of building a 2 X 12 Speaker box to go with the amp.

The bits I don't need to buy are valve sockets for the preamp and power valves, shields for the preamp valves, and retaining springs for the power valves, and the output transformer.

I might buy a brand new set of 12AX7 preamp valves, and a new set of 2 matched EL34 power valves for the amp next year.


Stay tuned......

apkane
14-05-2016, 08:51 AM
Hey Doc, this is very cool and something that I might have a go at in the near future I think....just don't let the Minister for War and Economics know. She's likely to photoshop a beard on me whilst I'm soldering away and report me to the AFP and have me taken away 'to assist with their inquiries'.
11259

Andy40
14-05-2016, 08:54 AM
What was the rough cost of parts Doc?

DrNomis_44
14-05-2016, 12:05 PM
Hey Doc, this is very cool and something that I might have a go at in the near future I think....just don't let the Minister for War and Economics know. She's likely to photoshop a beard on me whilst I'm soldering away and report me to the AFP and have me taken away 'to assist with their inquiries'.
11259


Hahaha....you should tell her to stop doing that, since I'm currently single I don't have to answer to a Minister for War and Economics, trouble is, I'm still learning how to budget my money, and worse still, I tend to be a bit impulsive with my spending, cheers for that mate, this amp I'm building has been a work-in-progess since I first started building it, I have been tweaking it as I've been building it and have lost count of the number of times I've revised the design, but I have learnt alot in the process.

DrNomis_44
14-05-2016, 12:10 PM
What was the rough cost of parts Doc?


It's very hard for me to give you a rough estimate, since my memory of how much I've spent on it is a bit rusty, some parts cost me nothing, but as an educated guess I've probably spent something like $300.00 or maybe $400.00, or even more so far on parts, but that is just a very rough estimate and I'm probably totally wrong.


The output transformer was probably the most expensive part to buy.

DrNomis_44
14-07-2016, 05:10 PM
Update:

Well, I'm finally going to "Bite The Bullet" and start ordering the new bits and pieces for my Valve Amp Head next Tuesday, did some browsing on the Evatco website and found that they have all the needed Pot values in their range of CTS pots, except 25K Pots, so, I did a quick google for 25K CTS Pots and found this website:

https://www.tubesandmore.com/products/new_products_0


Turns out they do stock 25K CTS pots so I'm going to replace all the existing pots installed on the amp chassis with some new CTS Pots, I do remember having some reliability issues with the Alpha 24mm Pots I've used in the Chassis previously, what's really strange and interesting is that only certain Pot values seem to suffer from reliability issues, I'm guessing that certain pot values tend to be more prone to the solder tags loosening due to heat-stress while being soldered to than others, so as a precaution I'm switching to CTS Pots, besides, some commercially manufactured amps use them anyway.

The 24mm Alpha Pots I used in the past were bought from Jaycar Electronics, and it appears that the lower value pots seem to be the most susceptible to heat-stress on the Solder Tags.

DrNomis_44
20-07-2016, 08:45 PM
Update:

Managed to make hard copy printouts of the Turret Board layouts, schematics, etc so I'm going to go ahead and order the materials I need to make the Turret Boards for my Sloclone 50 Amp Head tonight, will also see if I can get all the CTS pots ordered too.

DrNomis_44
20-09-2016, 08:30 PM
Update:


Since Adam has created a Forum section about Guitar amps, I'm thinking that it would probably be the most appropriate place for this thread, so if any of the mods could move this thread to that section, that would be much appreciated, cheers.

adam
22-09-2016, 04:42 PM
Done and done.

DrNomis_44
22-09-2016, 04:47 PM
Done and done.


Cheers mate, much appreciated.

DrNomis_44
22-09-2016, 04:58 PM
Okay, so re-building this amp and getting it all going again is going to be a project that's scheduled for next year, this will give me heaps of time to get my two guitar projects finished this year, so keep an eye on this thread cause I have some mini-tutorials planned for it, one of them is going to be about making Turret Boards for mounting all the components in the amp on.

dave.king1
26-09-2016, 03:56 PM
I was having a listen to some of the Lamington demos on YT and discovered a dude with a Train Wreck clone.

Circuits are over on Wattkins.com ( spelling is correct ) in the Tones Per Buck subforum under the thread title of Thrifty Wreck.

You will have to join the forum to get there but there is heaps of good stuff there

Here are a couple of links, you have to log in for the Wattkins one
http://www.wattkins.com/node/17851

The Trainwreck Pages
http://www.blueguitar.org/new/schem/...reck_pages.pdf

DrNomis_44
26-09-2016, 07:54 PM
I was having a listen to some of the Lamington demos on YT and discovered a dude with a Train Wreck clone.

Circuits are over on Wattkins.com ( spelling is correct ) in the Tones Per Buck subforum under the thread title of Thrifty Wreck.

You will have to join the forum to get there but there is heaps of good stuff there

Here are a couple of links, you have to log in for the Wattkins one
http://www.wattkins.com/node/17851

The Trainwreck Pages
http://www.blueguitar.org/new/schem/...reck_pages.pdf




Cheers for that, I'll check out those links tonight, I've heard lots of good things about both Trainwreck amps and Watkins amps too.


Just tried the Trainwreck Pages link and I get a 404-file not found error message.

dave.king1
26-09-2016, 08:41 PM
I got the same thing on the phone so I'll check the link out tomorrow and repost

DrNomis_44
26-09-2016, 08:45 PM
I got the same thing on the phone so I'll check the link out tomorrow and repost


Cheers mate, I think it might be caused by the files being moved to a different place and the link wasn't updated.

dave.king1
27-09-2016, 05:31 AM
Cheers mate, I think it might be caused by the files being moved to a different place and the link wasn't updated.

I read through a few of the 29 pages and then went back to the first page and simply copied and pasted the URL from the browser so I'm not sure what happened.

It could be that it's not mobile optimised which is rarely the case these days or maybe it shares some login information with Wattkins.com

Speaking of Watkins, Watkins Electronic Music was responsible for the Watkins Crybaby Wah pedal and the Watkins Copycat tape echo also the WEM amplifiers used by quite a few English rock groups back in the day.

A guitarist I worked with for a few years used both the Crybaby and Copycat I used a Klempt Echolette and Schaller Wah, the tape echoes were a proper pain because they went through at least one tape loop each night, the loops were relatively expensive so we spliced our own which was tedious and not a job to rush between songs

dave.king1
27-09-2016, 06:25 AM
Just turned the PC on and clicked the link and went straight in, so should be OK

http://www.blueguitar.org/new/schem/trainwreck/the_trainwreck_pages.pdf

I have my browser set to delete all cookies and empty the cache each time I close it so going straight in is not an artifact of a previous session

A bunch of circuits of the various versions of the Trainwreck Express here
http://www.blueguitar.org/new/schem/trainwreck/wreckxpr.pdf

Here is a clip of a genuine Train Wreck amp

https://www.youtube.com/watch?v=mL75YzhAcJ4

dave.king1
27-09-2016, 06:55 AM
The Trainwreck clone from Wattkins.com


https://www.youtube.com/watch?v=rj1pVyvCYy4

DrNomis_44
27-09-2016, 08:38 AM
Just turned the PC on and clicked the link and went straight in, so should be OK

http://www.blueguitar.org/new/schem/trainwreck/the_trainwreck_pages.pdf

I have my browser set to delete all cookies and empty the cache each time I close it so going straight in is not an artifact of a previous session

A bunch of circuits of the various versions of the Trainwreck Express here
http://www.blueguitar.org/new/schem/trainwreck/wreckxpr.pdf

Here is a clip of a genuine Train Wreck amp

https://www.youtube.com/watch?v=mL75YzhAcJ4



Those links worked for me too, managed to download the pdfs from both the links, cheers for that, maybe the server hosting those pdfs must have been experiencing some technical issues last night, I don't know for sure, anyway whatever it was it seems to have been resolved.

wazkelly
27-09-2016, 08:41 PM
Wow, sounds great but the techy bits are way beyond my skill level to even contemplate such a project.

DrNomis_44
28-09-2016, 01:07 AM
Wow, sounds great but the techy bits are way beyond my skill level to even contemplate such a project.


Don't worry, I'm still having trouble understanding some of the techy bits too so you're not alone, it is a bit of a steep learning curve, but the good news is that it does get easier the more you learn.

SteveO
15-10-2016, 01:29 PM
Hey Doc, I built this AX84 Hi-Octane Tube Guitar Amplifier some years back. It's a great sounding little amp. The wiring was easy but making the chassis etc was really the time consuming part and I had access to a pretty good workshop for the sheet metal etc. We had a laser cutter and made the front and rear decals. note that it does go up to 11.....

14425
I made a cover for the power transformer on a 3D printer as well.

14426
Rear View

14427

If anyone wants to build one I can add more photos on the inside.

DrNomis_44
16-10-2016, 10:03 AM
Hey Doc, I built this AX84 Hi-Octane Tube Guitar Amplifier some years back. It's a great sounding little amp. The wiring was easy but making the chassis etc was really the time consuming part and I had access to a pretty good workshop for the sheet metal etc. We had a laser cutter and made the front and rear decals. note that it does go up to 11.....

14425
I made a cover for the power transformer on a 3D printer as well.

14426
Rear View

14427

If anyone wants to build one I can add more photos on the inside.


That looks really cool, yes, the AX84 website has lots of great amp projects to build, there's a wealth of good info on that site and I have visited it quite a few times in the past, definitely one I could recommend adding to your bookmarks list.


Here's a link to the AX84 website for those who want to check it out, be sure to bookmark it if you find it interesting enough:


http://www.ax84.com/

Marcel
08-06-2017, 08:52 PM
I had a look at the AX84 site and despite there being some good stuff there I wasn't overly impressed.

My preferred site is http://schematicheaven.net/

From schematic heaven I devised my own hybrid of a JTM45 and 2204/4104 circuits plus a few of my own tweaks to build my own point to point wired 50W head.

There were a few obstacles to overcome, and changes due the re-use of the power and output transformers from the 6L6 based Playmaster (Electronics Australia) head that it was in a past life, but it has a new life now feeding a pair of Celestions the good vibes emanating from all my guitar builds...

I still have a few changes planned for it such as a post phase inverter master volume and some tweaks to the tone stack to name but two. It all fun, and it feels so good to have the knowledge that I built the whole lot from guitar go to sweet loud noises WHOA!!

DrNomis_44
08-06-2017, 08:59 PM
I had a look at the AX84 site and despite there being some good stuff there I wasn't overly impressed.

My preferred site is http://schematicheaven.net/

From schematic heaven I devised my own hybrid of a JTM45 and 2204/4104 circuits plus a few of my own tweaks to build my own point to point wired 50W head.

There were a few obstacles to overcome, and changes due the re-use of the power and output transformers from the 6L6 based Playmaster (Electronics Australia) head that it was in a past life, but it has a new life now feeding a pair of Celestions the good vibes emanating from all my guitar builds...

I still have a few changes planned for it such as a post phase inverter master volume and some tweaks to the tone stack to name but two. It all fun, and it feels so good to have the knowledge that I built the whole lot from guitar go to sweet loud noises WHOA!!


Wow, that's a nice little amp you have there mate, so how does it sound?

Marcel
08-06-2017, 10:44 PM
For a single channel amp and in one word....AWESOME !!

I have it in my shed where I do all my guitar builds and that is about 40m from the house (I live on acreage) and only once have I cranked the master up to 5, whereupon the wife complained that she had to turn the TV up because of my "noise"... noise that was IMHO clean, crisp and sharp... If I wind up the pre-amp gain it brings on quite a reasonable crunch right through to a half decent dirty.

It can't be as dirty as my standard JVM210C, nor match it on volume, but it does have its own character/tone which I put down as mostly being the ported speaker cabinet that I also built and the Celestion's the cab is loaded with.

It's certainly a more than an ideal 'workshop amp'...lol

Marcel
21-06-2017, 04:54 PM
While I pondered on the colour progression of my ES-1TL build I took the time to have a play in my favourite stomping ground ad fitted the post phase inverter volume control to my home made 50W (Master volume type 2103/2104/2203/2204) clone. refer http://schematicheaven.net/marshall.html under the series 'JMP 1959 Lead 50W' for the pdf circuit this is based upon.

If you look closely at the differences from this photo and the earlier photo you can see the dual gang 250k pot on the back panel that is the heart of the mod. In the bias circuit that feeds the EL34's there are (in Marshall designs) a pair of 220k resistors feeding the bias voltage to the output tube grids. The mod basically turns these two resistors into a variable volume control. Zero volume essentially connects the grids direct to the bias supply point, and 100% volume has the same effect as if the pot wasn't there. The Eagle eyed among you will notice that there are still 1M resistors going from the bias 2nd filter cap and the grid current limit resistors which are there to ensure there is always bias on the grids even if the post inverter volume pot has momentary open circuit moments when adjusted, and have the secondary effect of pulling the 250k pots back to 215k which is close enough to 220k as to not be bothered about.

I also added a 0.1uF across the high voltage supply to V1. This has the effect of reducing some of the noise that the cascaded stages in V1 are prone to make. The low input only uses half of V1, whereas the High input adds an extra 10dB of gain from the other half of the tube but sadly also adds to the noise floor. The cap helps to reduce the noise of the extra stage. It's getting better and I'm happy with it, but I know more can be done...

How does it sound?.... Clean on the low channel with flat EQ is wonderful with crisp bright highs and full lows . And with SD hot rails into the high channel I am left wondering why I ever spent money on OD pedals... and the wonderful thing is with the post phase inverter volume modification I can now wind it all down to evening bedroom volume levels or wind it up to ACDC concert levels without changing any of the drive through the three 12AX7's who do most of the work in creating a 'Grunge' or a 'Dirty' sound...

Now I need to work out a way of doing an 'effects loop', and a 'record line out'....

Zandit75
21-06-2017, 05:01 PM
While I pondered on the colour progression of my ES-1TL build I took the time to have a play in my favourite stomping ground ad fitted the post phase inverter volume control to my home made 50W (Master volume type 2103/2104/2203/2204) clone. refer http://schematicheaven.net/marshall.html under the series 'JMP 1959 Lead 50W' for the pdf circuit this is based upon.

If you look closely at the differences from this photo and the earlier photo you can see the dual gang 250k pot on the back panel that is the heart of the mod. In the bias circuit that feeds the EL34's there are (in Marshall designs) a pair of 220k resistors feeding the bias voltage to the output tube grids. The mod basically turns these two resistors into a variable volume control. Zero volume essentially connects the grids direct to the bias supply point, and 100% volume has the same effect as if the pot wasn't there. The Eagle eyed among you will notice that there are still 1M resistors going from the bias 2nd filter cap and the grid current limit resistors which are there to ensure there is always bias on the grids even if the post inverter volume pot has momentary open circuit moments when adjusted, and have the secondary effect of pulling the 250k pots back to 215k which is close enough to 220k as to not be bothered about.

I also added a 0.1uF across the high voltage supply to V1. This has the effect of reducing some of the noise that the cascaded stages in V1 are prone to make. The low input only uses half of V1, whereas the High input adds an extra 10dB of gain from the other half of the tube but sadly also adds to the noise floor. The cap helps to reduce the noise of the extra stage. It's getting better and I'm happy with it, but I know more can be done...

How does it sound?.... Clean on the low channel with flat EQ is wonderful with crisp bright highs and full lows . And with SD hot rails into the high channel I am left wondering why I ever spent money on OD pedals... and the wonderful thing is with the post phase inverter volume modification I can now wind it all down to evening bedroom volume levels or wind it up to ACDC concert levels without changing any of the drive through the three 12AX7's who do most of the work in creating a 'Grunge' or a 'Dirty' sound...

Now I need to work out a way of doing an 'effects loop', and a 'record line out'....


https://www.youtube.com/watch?v=25Nc8qI8iQM

Marcel
21-06-2017, 05:07 PM
LOL...!

Ask... and I'll answer... :-)

Guvna19
21-06-2017, 06:33 PM
Wow Marcel, That wiring is as good as I've seen, Looks Sweet as ! (whilst admitting my amateurish knowledge and total lack of experience)

Sadly , I have to accept the safe wiring skills required for such a project are currently beyond me

I have been lookin at valve amps for the last 2 months DIY / KIT /Schematics / speakers /cabs / new / 2nd hand. cant stop....lol

I dont really need a new amp or guitar ,and attempting to justify to the missus otherwise still needs further refining.

Seems obvious thats not your first amp build, What was your first build?

regards
Guv

Marcel
21-06-2017, 10:23 PM
Well Guv.... Thanks for the compliment, but to my eyes it still looks a bit like a dogs breakfast yet everything is there for a reason and a purpose. So you do realise the picture here, I'm 55 and I first started in electronics when I was just a cub in my early teens so there is just a little experience in there too ...;-)

If memory serves me rightly, my first actual amp... was back in the early '70's in my early years of High school, a 10+10W stereo amp to to go with my vinyl record player so I could play the newly released Deep Purple and 'Frampton Comes Alive' LP's that I had just acquired... Electronics Australia magazine (which is no longer in circulation) had published a circuit, and I convinced my dad to get me the parts from Radio Parts (RPG) on Spencer St. in Melbourne and what I couldn't get there I got from a new upstart company called Dick Smith which I think back then was on Elizabeth St in the CBD. By the time I finished year 10 in '77 I had built many things one of which was my own 8bit CPU computer in a laptop attaché case which I used to control my brothers train set and all the learning made my subsequent formal electronics training in the RAAF a relative breeze easy experience.

If you are new to it or anything Gav... my suggestion is to start small, and when you have repeated success then get more adventurous. Aside from building electric guitars from PBG there is Jaycar who have a few interesting and useful cheap kits for musical/guitar projects to help learn basic electronics with...

As for mains powered kits and tube amp builds, I strongly suggest getting at least some formal training, particularly in regard to electrical safety and the high voltages that are found in tube circuits. Without the training it is all too easy to develop bad practices which will ultimately result in tragedy... And nobody wants tragedy.

Too Many people dismiss it but electrical safety is a big concern. I do hold a fully endorsed restricted electrical licence (NREL) that I studied for through TAFE. It is worth the effort. It also means I know my amp is safe yet I also know I could never sell my amp due to its one glaring failure, and I think few here could pick what that failure is...

DrNomis_44
22-06-2017, 08:17 AM
That's the same approach I took to learning Electronics, I started off with the simple circuits and when I felt that I understood how they worked, I progressed onto more complex circuits, same with actually building them.

Guvna19
22-06-2017, 08:57 AM
Cheers Marcel / Doc, no idea what the said 'glaring failure is'

My Dad was an electrician and i have 2 older brothers in W.A. one being an ex Navy electronics technician and the other a highly qualified sparky. unfortunately I dont get to utilize their skills as they both work heavy shifts in the mining industry and have little spare time.
They all used to chat electronics and engage in dozens of Dick smith projects at the dinner table, which at the time bored me to tears so I chose an alternate career beginning as an apprentice painter. Now aged 45 and still in the paint industry, i have a growing interest in the guitar-amp related electronics area and wish i paid more attention at the dinner table.
I will look into some jaycar projects as you suggest. Know of any projects that serve as usefull tools for future projects , (i dunno, like a voltage meter or somthing?)

cheers
Guv

Marcel
24-06-2017, 06:18 PM
I've seen at my local Jaycar store some stomp box kits. Fuzz box type things. Never tried one as I have a TS9 and two other distortion pedals so never felt the need myself to build a fuzz kit. Some of the loud speaker audio amp kits look interesting. It is more a decision of what you have a need for at the time and is building a kit the less expensive way to go...

One kit I did build recently was a DC motor speed controller, with the aim of building a pickup wining machine. Runs on 12VDC so a small sealed lead acid (SLA) battery and a 12V plugpack would see you all powered up. Could even run it on a few D cells if you wanted. I'm still working out how to add a counter so I get the right number of turns on any pickups I may wind.

As for multimeter kits I think buying a complete digital meter is a cheaper and more reliable choice when first starting out as you need to be able to trust the meter you are using. But if you can find a cheap analogue meter then grab it as they are great for testing pickup polarities.

Marcel
24-06-2017, 06:39 PM
That's the same approach I took to learning Electronics, I started off with the simple circuits and when I felt that I understood how they worked, I progressed onto more complex circuits, same with actually building them.

That is so right Doc. And I did the same...

Start with simple things with only a few components. learn a few of the laws like ohms law and the power law, then add things like how to calculate impedance of a cap or a coil, and so on... they are all steps that all who are interested must learn and follow,... step by step,, and all the while applying what you learnt to your build...

Not that much different in principal to building a guitar really....lol

DrNomis_44
24-06-2017, 09:20 PM
That is so right Doc. And I did the same...

Start with simple things with only a few components. learn a few of the laws like ohms law and the power law, then add things like how to calculate impedance of a cap or a coil, and so on... they are all steps that all who are interested must learn and follow,... step by step,, and all the while applying what you learnt to your build...

Not that much different in principal to building a guitar really....lol


It was only when I started doing formal studies in Electronics that I was finally able to understand Impedance and how it varies with frequency in Inductors and Capacitance, I also learnt that you can cancel-out the effects of Inductive-Reactance and Capacitive-Reactance if you make both the Inductor and the Capacitor equal in value, at some frequency the two equal and opposite-phase Reactances will cancel each other out, and you will be left with pure DC resistance, which is usually a very low value, this is basically how a passive series LC bandpass filter works, my Fender Super Twin uses them in it's EQ circuit, each frequency band is determined by the relative values of the Inductor (L) and Capacitor (C), pretty interesting how they did things back then, nowadays circuit designers use a special Op Amp circuit to replace/simulate an Inductor, it's a circuit called a Gyrator, basically it inverts the behaviour of a capacitor so that it looks like the behaviour of an Inductor.

Hopefully I'm remembering my electronics theory correctly.

Marcel
25-06-2017, 01:43 PM
Yeah Doc, can't fault what you wrote so your theory is up there...

Personally, I still can't get over the fact that some people (particularly on other forums) truly think that an active circuit using an Op-amp and a capacitor imitating and inductor is better than a real (passive) inductor made from simple copper wire.... True, the Op-amp circuit maybe more versatile, but still it amazes me...

But I do appreciate some of the wicked and awesome things than can be done with electronics (in all its forms) these days. I've worked on all sorts of gear, some that operate from DC all the way through to gear that works on damn near daylight yet there near isn't a day goes by where I don't encounter some new way of doing things with electronics... so it is refreshing to 'dive into' a good tube job where the technology hasn't really changed much in decades.

One thing that does get 'up my goat' and yet I often have a good laugh over is the fault finding techniques that are there for all to see on YouTube... There are few that achieve in my opinion a 'Good' status, and one or two who are expert, but where I get the best laughs are those who fumble about and change parts willy-nilly for an hour or two until the poor amp gives in and starts to work again...

DrNomis_44
25-06-2017, 02:54 PM
Yeah Doc, can't fault what you wrote so your theory is up there...

Personally, I still can't get over the fact that some people (particularly on other forums) truly think that an active circuit using an Op-amp and a capacitor imitating and inductor is better than a real (passive) inductor made from simple copper wire.... True, the Op-amp circuit maybe more versatile, but still it amazes me...

But I do appreciate some of the wicked and awesome things than can be done with electronics (in all its forms) these days. I've worked on all sorts of gear, some that operate from DC all the way through to gear that works on damn near daylight yet there near isn't a day goes by where I don't encounter some new way of doing things with electronics... so it is refreshing to 'dive into' a good tube job where the technology hasn't really changed much in decades.

One thing that does get 'up my goat' and yet I often have a good laugh over is the fault finding techniques that are there for all to see on YouTube... There are few that achieve in my opinion a 'Good' status, and one or two who are expert, but where I get the best laughs are those who fumble about and change parts willy-nilly for an hour or two until the poor amp gives in and starts to work again...


Yep, some people forget to realize that Op Amps, being active devices, do introduce noise and distortion into a circuit, that's the nature of active devices, valves introduce noise and distortion into a circuit too but they produce different distortion harmonics due to the non-linearity inherent in valves, the noise is produced by the electrons boiling off the cathode during thermionic emission.

When I'm fault-finding a piece of electronic equipment I always try to maintain a logical approach to it, and treat it as if I'm a detective working on solving a mystery.

Marcel
25-06-2017, 08:33 PM
You often see comments like that on videos called "Repairing my Brand XYZ tube amp" where viewers see the video as a detective hunt...

My giggles come mostly from what those guys do during their 'detective hunt'. Particularly when they go off on a tangent chasing some clue to nowhere as they more often than not they have failed to understand what the circuit is doing or should be doing, or they misinterpret a meter reading, or they fail to take any readings with a meter at all. They just jiggle and swap tubes, tap away all over the chassis, and start swapping other bits until finally after 45 minutes of video they go back to what they discovered 10 minutes in and replace the real culprit. Entertainment with a bit of learning thrown in.

My fault finding usually follows the half split rule. This is where you view the faulty whatever as a complete system with an in and a out, or a start and a finish, and you divide it in half. If what you are getting at that point is okay then you know everything before that point is fine and your fault lies in the other half. You then repeat the process on the 'faulty' half, and keep repeating until you get to a point where you can't split it any more. At this point you need to know what that part is doing and also know from the schematic and your experience what it should be doing, and the research any differences. There is a lot more to it but that is the essential basics I follow.

Did you know that EVERY component adds noise. Active devices like tubes and transistors add the most, but resistors and caps and coils and even wire add their fair share too..... all those electrons randomly bouncing from atom to atom in every component....

On another note, A video you might like to watch.... Mullard tube manufacture film from the early '60's... https://www.youtube.com/watch?v=GDvF89Bh27Y

DrNomis_44
25-06-2017, 08:50 PM
You often see comments like that on videos called "Repairing my Brand XYZ tube amp" where viewers see the video as a detective hunt...

My giggles come mostly from what those guys do during their 'detective hunt'. Particularly when they go off on a tangent chasing some clue to nowhere as they more often than not they have failed to understand what the circuit is doing or should be doing, or they misinterpret a meter reading, or they fail to take any readings with a meter at all. They just jiggle and swap tubes, tap away all over the chassis, and start swapping other bits until finally after 45 minutes of video they go back to what they discovered 10 minutes in and replace the real culprit. Entertainment with a bit of learning thrown in.

My fault finding usually follows the half split rule. This is where you view the faulty whatever as a complete system with an in and a out, or a start and a finish, and you divide it in half. If what you are getting at that point is okay then you know everything before that point is fine and your fault lies in the other half. You then repeat the process on the 'faulty' half, and keep repeating until you get to a point where you can't split it any more. At this point you need to know what that part is doing and also know from the schematic and your experience what it should be doing, and the research any differences. There is a lot more to it but that is the essential basics I follow.

Did you know that EVERY component adds noise. Active devices like tubes and transistors add the most, but resistors and caps and coils and even wire add their fair share too..... all those electrons randomly bouncing from atom to atom in every component....

On another note, A video you might like to watch.... Mullard tube manufacture film from the early '60's... https://www.youtube.com/watch?v=GDvF89Bh27Y


I think that a lot of those Youtube service techs probably fail to realize that the actual fault-symptoms can be a very valuable clue to where the fault is most likely to be, I'm currently working on tracing the source of some crackly noise in my Moen Pretty Dolly Delay pedal, so far what I've done is given the pots a spray with some contact cleaner, it didn't fix the crackly noise but it eliminated one cause, I'm starting to suspect that the noise is being generated by a JRC4558 IC, but I may be wrong, I'm going to try substituting a TLO72 IC for it, I know that JRC4558 ICs are inherently noisy, and since the TLO72 is a low noise pin-for-pin compatible IC, it should work fine, other than the noise issue the pedal works fine, it's just a bit too noisy for use on my pedal board, my Boss RE20 Space Echo is much quieter in comparison, but I might just do some tracing with my Oscilloscope first though.

Actually, I didn't know that even wires generate noise, I guess if it has moving electrons in it, anything in the circuit can generate noise regardless if it's active or passive, even reverse-biased silicon diodes will generate noise, that's the classic way of generating noise in Synthesizers, either a reverse-biased diode or Transistor B-E junction.

I'll check out that link you posted, cheers.

Marcel
26-06-2017, 09:21 PM
My worst experiences with noise were during World Expo 88 in Brisbane.

The first was with the new you-beaut latest model 32 band stereo graphic equalisers that were in use everywhere and used a proprietary chip that often went noisy. I must have replaced at least 100 of those 12 pin inline goop encased sub-boards that held the chip which for nil obvious reason would randomly simply start generating higher levels of hiss that was not unlike a reverse biased diode.

The second was the Soundcraft 40ch/16bus foldback console on the river stage. The sound guys and the artists all complained about the poor noise floor while doing shows, so we contacted Soundcraft in the UK. They were very nice yet somewhat apprehensive when they advised of a modification that could be done to this $150k console. Ultimately after many phone calls and various assurances I performed the modification which involved a number of wire and solder changes and taking a dremmel to every board in the desk... I had a 11hr window to do the work which took 9hrs with the dremmel and all the while in the back of my head I knew that this one desk was worth more at the time than most inner city Brisbane CBD apartments, plus the desk had to be back in service by 10am.... The mod worked fine but it was Yay, and team me totally stressed out and dead dog tired by the end...

A side note of trivia - my avatar is a pic of some Gold Silk embroidery on a Black denim jacket I had done at the China pavilion during the Expo...

DrNomis_44
26-06-2017, 10:25 PM
My worst experiences with noise were during World Expo 88 in Brisbane.

The first was with the new you-beaut latest model 32 band stereo graphic equalisers that were in use everywhere and used a proprietary chip that often went noisy. I must have replaced at least 100 of those 12 pin inline goop encased sub-boards that held the chip which for nil obvious reason would randomly simply start generating higher levels of hiss that was not unlike a reverse biased diode.

The second was the Soundcraft 40ch/16bus foldback console on the river stage. The sound guys and the artists all complained about the poor noise floor while doing shows, so we contacted Soundcraft in the UK. They were very nice yet somewhat apprehensive when they advised of a modification that could be done to this $150k console. Ultimately after many phone calls and various assurances I performed the modification which involved a number of wire and solder changes and taking a dremmel to every board in the desk... I had a 11hr window to do the work which took 9hrs with the dremmel and all the while in the back of my head I knew that this one desk was worth more at the time than most inner city Brisbane CBD apartments, plus the desk had to be back in service by 10am.... The mod worked fine but it was Yay, and team me totally stressed out and dead dog tired by the end...

A side note of trivia - my avatar is a pic of some Gold Silk embroidery on a Black denim jacket I had done at the China pavilion during the Expo...


Now that you mentioned Soundcraft gear, a good mate of mine got me to do some restoration work on his 80's vintage 28 Channel Soundcraft mixing desk, apparently some rats or other rodents got into it and randomly chewed the ribbon cabling to pieces, I had the job of cutting out all the worst-chewed pieces and splicing all the good bits together, I had to literally solder and heatshrink 80+ individual strands of wire every time I spliced the ribbon cabling together, incidentally the ribbon cabling was what distributed the audio signals from each of the 28 Channels, so it was a big job, I eventually got it to the point where it was something like 80% working and had to turn my attention to a mini-jack patch panel, I was getting signal to pretty much every part of the patch panel as it was supposed to, but there was one mini-jack that appeared to be faulty, I decided to use a X10 magnifying loupe to give the suspect jack a good eyeball and as it turned out the cause of the fault turned out to be an insignificant piece of lint wedged between two contacts, I cleaned it out and the mini-jack worked normally again, the guy who owns the Soundcraft desk runs a recording studio and wants me to do a re-cap job on all the channel strips to get each one sounding consistent so he can use it as part of his studio setup, most of the caps in the channels are electrolytics which I'm guessing are easily over 20 years old by now and are probably due for replacement, they are all RT style that are wrapped in a translucent-blue film, looks like a fun job for me, I still have fond memories of the work I did on it, tracing out all the signal paths with my Signal-Generator and Oscilloscope.

Marcel
27-06-2017, 09:04 AM
Soundcraft were state of the art back in the '80's. Very top end gear along with SSL and Yamaha. Interestingly back then on the wholesale and the servicing side both Yamaha and Marshall in Australia were handled by the same people. Not sure if it is still the case today.

For a cap replacement request I'd be tempted to do audio frequency response tests first across the whole desk, find the worst slots, repair them, and then repeat the repair on all the other channels. That way you end up only replacing what's needed to restore 100% performance. Unless the client specifically asks for it and is prepared to pay then doing a wholesale replacement can get substantially more expensive in both time and money, and may not necessarily cure all problems.

I have a 20/8/2 Soundtraks Megas Studio desk from the late '80's that has an interesting Aux send fault. None of the 6 sends work and the supply resistor for the sends in the Master bus module gives up its smoke the moment you turn the desk on. Have swapped the chips and most of the caps but without an accurate circuit this MIDI controlled desk is proving difficult (a bastard in every possible sense of the word) to repair which is a shame as it is a fantastic home studio desk if I could get the sends working... 4 band dual parametric EQ, 6 sends, 16 mono and 4 stereo modules, 8 bus, dual monitor volumes, LED metering, MIDI mute control/recall,..... Thankfully nil mice have ever been in there before me...lol

Those dirty contact faults can be annoying and pesky....lol ... and I'm surprised you didn't get a replacement ribbon.

DrNomis_44
27-06-2017, 06:38 PM
Soundcraft were state of the art back in the '80's. Very top end gear along with SSL and Yamaha. Interestingly back then on the wholesale and the servicing side both Yamaha and Marshall in Australia were handled by the same people. Not sure if it is still the case today.

For a cap replacement request I'd be tempted to do audio frequency response tests first across the whole desk, find the worst slots, repair them, and then repeat the repair on all the other channels. That way you end up only replacing what's needed to restore 100% performance. Unless the client specifically asks for it and is prepared to pay then doing a wholesale replacement can get substantially more expensive in both time and money, and may not necessarily cure all problems.

I have a 20/8/2 Soundtraks Megas Studio desk from the late '80's that has an interesting Aux send fault. None of the 6 sends work and the supply resistor for the sends in the Master bus module gives up its smoke the moment you turn the desk on. Have swapped the chips and most of the caps but without an accurate circuit this MIDI controlled desk is proving difficult (a bastard in every possible sense of the word) to repair which is a shame as it is a fantastic home studio desk if I could get the sends working... 4 band dual parametric EQ, 6 sends, 16 mono and 4 stereo modules, 8 bus, dual monitor volumes, LED metering, MIDI mute control/recall,..... Thankfully nil mice have ever been in there before me...lol

Those dirty contact faults can be annoying and pesky....lol ... and I'm surprised you didn't get a replacement ribbon.


Reason why I didn't get a replacement ribbon was that there weren't any available so I literally had to go through and cut out all the worst chewed bits and splice all the good bits together, it took a while but I managed to get it all done, it was great for exercising my patience....lol.

It sounds to me that there might be a short-circuit somewhere after that supply resistor for the sends in the master bus module, that's the first thing I'd be suspecting, and it's probably the reason why the sends aren't working, you could try having a good look underneath the circuit board with a magnifier to see if there are any slivers of solder creating unintentional shorts, I'd also try measuring the voltage on either side of that resistor too, I agree, trying to service a piece of gear without a good circuit diagram is like trying to solve a mystery blindfolded, I wish all manufacturers would get their heads out of that "gotta protect our designs" mentality and start producing decent, ie clearly legible, circuit diagrams and easily obtainable service manuals, but a lot of electronic gear these days are designed with planned obsolescence included in it, back in the early days of electronic gear manufacture, things were designed and built like tanks.

Marcel
27-06-2017, 08:46 PM
I know exactly where you are on the map with that Doc, and I'm right beside you.... Protecting IP by not publishing circuits for technicians in my mind is the quickest way to go from fault to rubbish dump and earning yourself a rubbish reputation at the same time. Sadly many management types are taught and only see the situation as 'turnover of product'....Which is fair enough if the item is sold for a few bucks, but that thinking makes no sense once the product gets past a weeks wage worth in value... Unfortunately most computerised products like smart phones and the like have morphed into their own little modular world in the 'circuits' discussion...

For the moment the Soundtraks desk is safe-n-sound sheltering in the too hard basket. Multi layer boards stacked 3 deep on a 2 module wide frame along with short ribbon cable lengths and nil circuit, and a huge lack of urgency. But one day, when I'm more in the mood and have the need...
I did find an UK enthusiast group for the desk, I got channel module circuits from them but they don't have the right circuit for the master module of my desk. Actually they were surprised to learn that my desk has MIDI which makes it a rather special rarity. Also found out that in the UK it is a very popular type of desk for analogue affectionardo small studio owners as it has nil digital audio sections at all and enjoys the highly desirable traits of a superb noise floor and very effective and acoustically pleasing EQ.

Marcel
29-06-2017, 09:13 AM
Found this of FB. Thought it might be of relevance when choosing caps for an amp (or guitar) build...

http://zerocapcable.com/?page_id=224

Simon Barden
29-06-2017, 06:57 PM
Not a very good test at all IMO. They measured the capacitance, then they put a recording of a guitar pickup through a digital filter using the capacitor value as either a value in the filter or using it to determine the filter's cut-off point. You then hear (if there is a sound clip) the recorded signal played back through the filter - which gives the capacitor only signal (as if the tone control has been turned town to 0).

Now you aren't going to hear any real tone difference when so much of the signal has been filtered out (and using mp3s doesn't help either), so you do need to hear it with just bit of the tone rolled off - which didn't happen. Also there must be more subtle things happening that you aren't going to hear with a muffled and data compressed sample. I don't expect to hear much difference at all between the capacitor types, but I'm sure that the different dielectrics must have some varying frequency-dependent characteristics.

Also, whilst fairly slight, there would still be some interaction between the tone control and the pickups as the tone control is adjusted. Their sound clip was taken direct from a pickup (hopefully into a hi-Z input) with no tone pot in circuit. If you want to do a test, you should do it properly. I'd have used a multi-turn pot with a lock for the tone control, so I could set some mid-position settings accurately and with no chance of accidentally moving the pot between different capacitors.

I'm not sure how you could get a consistent signal through the pickup (I get their point), But there must be a means of inducing a repeatable signal from an external device (e.g. TC Electronics send messages to their effects pedals through pickups with sound from a mobile phone).

Then I'd look at frequency response and frequency over time response charts of the signals to compare them. If there was next to no difference, then I'd say that there really no difference between capacitors. However, they do mention that ceramic capacitors are prone to microphony, so best not to use them. But other capacitor types, though less prone to microphony, may still be affected slightly by loud noise, so this should also play a part in the test, so add a guitar amp playing back at both quiet and loud volumes and see if there is any difference.

Marcel
29-06-2017, 08:51 PM
I had good laugh when I saw this report, and I never bothered listening to the sound samples as I concluded after reading the entire text that by their test methods they were not going to see any differences anyway.

My own feelings about this topic are mixed. On one hand as a tech I can see that a 0.022uF cap is exactly that and given a fixed frequency and circuit to work in then the performance of that cap should not vary if it is replaced with any other cap of the same value.... BUT.... we are not dealing with a fixed frequency, and we are dealing with a complex LCR circuit which does have a semi-random mechanical aspect to the equation, and we are dealing with human hearing which has immeasurable variables from person to person so it is conceivable to me that replacing one cap with another will have an effect which is interpreted differently between different people.

To quantify that 'interpretation' is a difficult if not near impossible task. Minor changes in capacitance value, ESR, stray coupling, the hand that strikes the string are but few of the things that will 'colour' any persons interpretation on 'how it sounds' or if 'it sounds good'. And those few variables are relatively minor when compared to the biggest factor of 'what the listener believes'. Faith in all its forms has a huge impact on our choices and opinions.

Personally I think belief plays an important part of any performance. Be it a politician on a podium or a musician on a stage or a soldier in a army or a pilot in an aircraft or a cook in a kitchen,.... if you believe in yourself, your gear, those around you, your tools, those supporting you then your performance will excel.... and 'tone caps' are a (small) part of that excellence...

Simon Barden
29-06-2017, 09:00 PM
I'm not one for using the tone control on my guitars except on rare occasions and only to get a more jazz-like sound, so any of the finer nuances would be generally lost on me anyway, though I do now normally fit Sprague orange drops to my guitars (If only because their size and stiff legs make them easy to fit) but have bought some PIO caps from Bareknuckle to fit on my ES-3 kit as I was also buying some other bits from them at the time and thought - why not!. They weren't ridiculously expensive, maybe twice their price for orange drops, so I thought it worth a go.

Marcel
29-06-2017, 09:11 PM
I'm guilty of that too Simon. Bought a 10 pack of 0.022uF Orange drops at 3 times the price that I can buy Vishnay or Panasonic caps of the same value off my wholesaler. It was a bit of a waste as most of my current heard of guitars are fitted with humbuckers... You live and learn...
I agree that the Orange drops on a physical/mechanical level are very nice to work with. Haven't tried any PIO caps from Barenuckle.

DrNomis_44
29-06-2017, 09:12 PM
Before I moved to Darwin in 2000, I bought a kit from Jaycar Electronics which was for building a device called an ESR meter, you'll probably know what ESR stands for Marcel, but for the benefit of other members, ESR is short for Equivalent Series Resistance, now the ESR of a capacitor is an important specification, in Electrolytic Caps you want the ESR to be as low as possible, usually it's about less than an Ohm in fairly large value Electrolytic Caps, the ESR of a Cap is the Effective Series Resistance that the cap presents to AC, and is a very good indication of the health of the Cap because when the Cap goes bad and dries out, the ESR skyrockets in value, or goes high, lower value caps, eg say a .022uF/600V PIO type, will have a higher ESR than say a 47uF/450 V DC Electrolytic, Low ESR is an important spec for Caps because you tend to find a lot of low ESR Caps in modern Switchmode Power Supplies.

I might see if I can dig up my ESR meter and do some restoration work on it so that I can use it again, I think it just needs a couple of new test leads made for it, and maybe a new 9V battery clip, if I can't find it I might see if I can buy a new ESR meter kit from Jaycar cause there's supposed to be an updated one.

I think at least one of my DIY guitars uses a .1uF PIO cap as the tone cap, they are pretty good sounding, to my ears the common garden-variety 100V Greencaps seem to have a tone that has a harsh high-end to it, or maybe I'm just imagining it....lol.


When you choose a Cap for use in an electronic circuit, you have a few criteria that the Cap needs to meet, for me those criteria are as follows:


1, Working Voltage- (Very Important) The Cap needs to have a Dielectric (plate insulator) that is able to withstand the expected voltages in the circuit when the circuit is energized, or powered up, otherwise the Dielectric will puncture and develop a short-circuit.

2, Tolerance- (Not so important in some cases) The tolerance of a Cap is how much it actually measures in value +/- the marked value, most modern Electrolytic caps can actually measure anywhere from +/- 10-20% of the marked value on the Cap, in some cases, like in tuned radio circuits, or audio filters you want the tolerance to be fairly tight, note that most of the time it's not that critical.

3, Physical size- This is relatively self-explanatory, you wouldn't want to try and use a huge oil-filled can-cap in a circuit designed to fit in a case that's about the size of a matchbox.

4, Age- Again self-explanatory, you wouldn't want to use a Cap that's so old it's literally crumbling away to dust.

Simon Barden
29-06-2017, 10:54 PM
And on no.1, the working voltage should ideally be half that or less of the caps rated value. Above that, the capacitance value drops off (so you might need to use a bigger value capacitor than normal if that's the case). And when working with AC circuits, if the cap only has a DC voltage value on it, then remember that the RMS voltage of an AC circuit is less than the peak voltage achieved by the AC signal. For a sine wave this is 41% greater than the RMS value.

Marcel
29-06-2017, 11:04 PM
I think at least one of my DIY guitars uses a .1uF PIO cap as the tone cap, they are pretty good sounding, to my ears the common garden-variety 100V Greencaps seem to have a tone that has a harsh high-end to it, or maybe I'm just imagining it....lol.



Many years ago I ran a workshop in the Valley in Brisbane servicing all sorts of amps and gear. I very quickly learnt that happiness of the customer was paramount, and a substantial part of that happiness was catering to their beliefs about gear. Which gear sounds best, which gear is crap, is it worth it to do this or that modification, and so on. Quite often I'd end up replacing a perfectly serviceable part with another because the other had some reputation that the muso wanted in his rig. I'd charge the muso accordingly , they'd walk away happy, and recommend me to their friends... so it was all good. Nine times out of ten I couldn't tell any difference, but they could, so I lived with it, it was their money that they were spending. In a sense I felt they were buying happiness, which made them play better, but I couldn't tell.... These days I have the time to spend looking at and repeating for myself those changes I did back then, and despite my own issues (Tinitinitus or whatever) and in my own way I'm starting to see and hear what those muso's back then and now were on about.... go figure...

My ESR meter works fine, as does my Z meter... I'll post some pix soon to illustrate what you said there Doc... I have a few new and old dud caps floating around here somewhere...

DrNomis_44
29-06-2017, 11:14 PM
Many years ago I ran a workshop in the Valley in Brisbane servicing all sorts of amps and gear. I very quickly learnt that happiness of the customer was paramount, and a substantial part of that happiness was catering to their beliefs about gear. Which gear sounds best, which gear is crap, is it worth it to do this or that modification, and so on. Quite often I'd end up replacing a perfectly serviceable part with another because the other had some reputation that the muso wanted in his rig. I'd charge the muso accordingly , they'd walk away happy, and recommend me to their friends... so it was all good. Nine times out of ten I couldn't tell any difference, but they could, so I lived with it, it was their money that they were spending. In a sense I felt they were buying happiness, which made them play better, but I couldn't tell.... These days I have the time to spend looking at and repeating for myself those changes I did back then, and despite my own issues (Tinitinitus or whatever) and in my own way I'm starting to see and hear what those muso's back then and now were on about.... go figure...

My ESR meter works fine, as does my Z meter... I'll post some pix soon to illustrate what you said there Doc... I have a few new and old dud caps floating around here somewhere...


Cheers mate, that would actually be good so that other forum members can see what it's all about, it'll be interesting in any case.

DrNomis_44
29-06-2017, 11:33 PM
And on no.1, the working voltage should ideally be half that or less of the caps rated value. Above that, the capacitance value drops off (so you might need to use a bigger value capacitor than normal if that's the case). And when working with AC circuits, if the cap only has a DC voltage value on it, then remember that the RMS voltage of an AC circuit is less than the peak voltage achieved by the AC signal. For a sine wave this is 41% greater than the RMS value.


Good point there Simon, I've actually got first hand experience of what happens to an Electrolytic cap if it's working voltage is exceeded, I've got a variable DC power supply that I built from a kit of parts that I bought from Jaycar Electronics, one day I powered it up so I could use it to power a circuit I had breadboarded on one of my solderless breadboards, about a minute after I turned the power supply on I heard a loud bang from inside the power supply, I quickly powered it down and disconnected it from the mains power, after I had recovered my nerves I took the top plastic cover off the power supply so I could have a look inside to see what caused the loud bang, it turned out to be very obvious just what caused the loud bang, one of the main power supply filter caps just after the bridge rectifier had exploded and blew it's aluminium casing off so that the casing was now lying on the bottom of the power supply's plastic casing, as luck would have it, I still have the pics I took of the exploded cap so I'll post them here.


Here we go, this is to illustrate exactly what can, and will happen when a cap exceeds it's working voltage:

20303

20304

20305


As you can see in the pics, the cap in question was a 2200uF/25V Electrolytic cap, my guess is that the voltage across it was a bit too high and the result is what you see in the pics, the other 2200uF/25V cap is in parallel with it so maybe the one that exploded was inherently faulty in some way when it was manufactured, I ended up replacing both of them with a couple of new 2200uF/35V caps if my memory serves me right, and the power supply has never given me any more trouble since.


A very classic example indeed.

Marcel
30-06-2017, 09:59 AM
A Dud cap tested.

It has the correct uF reading on the capacitance meter and reads high ohms when tested with an ohm meter, but it also has high ESR and is leaky when a high DC voltage of 250VDC is applied. This failed cap will allow hum to pass and will sag badly when the amp is pushed causing loss of dynamics and loss of headroom.

Marcel
30-06-2017, 10:19 AM
A almost good (and very old) cap tested

This cap has lower capacitance than the marked value, close to 20% less. The insulation resistance is good at near 2Mohm but the ESR is marginal. So given it is quite old and was borderline performance on 2 out of 4 tests it was swapped out for a new HT filter cap. Truth be told this cap could easily have seen a few more years faithful service and nobody would have complained, particularly the wallet of its previous owner.

I've included a precautionary photo of the insulation tester and a volt meter. Note that the Insulation tester I use sends out negative 260VDC. This is crucially important thing to note when you testing large filter caps as they very rarely respond well to incorrect voltages being applied to them as illustrated in Doc's earlier post... Check the polarity of the insulation tester that you are using before doing filter cap tests like this...

DrNomis_44
30-06-2017, 11:13 AM
Cheers for that Marcel, that ESR meter looks exactly like the one I built from a kit of parts I bought from my local Jaycar Electronics store, I'll see if I can find it and do some restoration work on it if it needs it, it's a very useful piece of test gear to have cause it will easily identify caps that have gone bad but otherwise look perfectly okay.

Marcel
01-07-2017, 08:35 AM
In recent days I've been trawling through circuit diagrams of amps looking for a half decent 2xEL84 output design with two or three 12AX7 driver tubes to build and I think I have found something I like. It is essentially a Marshall circuit with 18W output which has nil negative feedback circuit and even includes a 2nd channel with tremelo. For something to do at night I might try and rearrange things into a single channel design so it can have switchable clean/crunch/OD and/or tremelo on the one input jack...

Dedman
01-07-2017, 08:47 AM
I've always thought of electrical wiring the same as plumbing....except with acid.

Marcel
04-07-2017, 12:07 PM
I've taken the plunge.... Bought all the electrickery bits I need but don't yet have to make me a 15W EL84 amp. A couple of transformers, a few HV caps and a few tube sockets only set me back about AU$400.... Just need a pretty box to house it all in and a pair of EL84's.

DrNomis_44
04-07-2017, 01:00 PM
I've taken the plunge.... Bought all the electrickery bits I need but don't yet have to make me a 15W EL84 amp. A couple of transformers, a few HV caps and a few tube sockets only set me back about AU$400.... Just need a pretty box to house it all in and a pair of EL84's.


You could try doing what I did and make a chassis/box from 2mm Aluminium sheeting, I found that 2mm Aluminium sheeting is not very hard to cut with a jigsaw, although you do need some method of folding the sides and tabs up, like a panbrake metal-bending machine, if I could get a decent one I'd be doing more amp builds.

dave.king1
04-07-2017, 02:12 PM
You could try doing what I did and make a chassis/box from 2mm Aluminium sheeting, I found that 2mm Aluminium sheeting is not very hard to cut with a jigsaw, although you do need some method of folding the sides and tabs up, like a panbrake metal-bending machine, if I could get a decent one I'd be doing more amp builds.

Get some 50x50x6mm angle iron from that unmentionable place and cut it to suitable lengths and stick it in the bench vice, I folded all of the alloy in the car in my avatar by hand using various makeshift mandrels and jigs.

1.6mm alloy sheet cuts OK with a jigsaw if you use a fine blade and run it at high speed.

Word of warning, make sure you use separate blades and flap wheels for steel and aluminum because the particles become highly combustible when mixed and get hot enough. I don't speak from experience with this advice but know a few guys who do

Simon Barden
04-07-2017, 04:33 PM
Aluminium + iron oxide = thermite.

DrNomis_44
05-07-2017, 12:08 AM
Cheers for that and very good point, yes we don't want other forum members accidentally starting huge fires.


The interesting thing to note is that when you bend a piece of metal, it does have a tendency to heat up a bit at the point where the bend occurs, but it doesn't get hot enough to ignite flammable material, unless the metal is bent multiple times in the same place at a high rate, and then the metal suffers from what's called "Metal fatigue" and then breaks at the point where it is bent repeatedly.

Marcel
11-07-2017, 08:21 PM
You could try doing what I did and make a chassis/box from 2mm Aluminium sheeting, I found that 2mm Aluminium sheeting is not very hard to cut with a jigsaw, although you do need some method of folding the sides and tabs up, like a panbrake metal-bending machine, if I could get a decent one I'd be doing more amp builds.

Instead of folding my own I've chickened out and bought a pre-made case from Jaycar. Main reason is it will be fully sealed on the wiring side so the cage that will eventually cover the tubes will not need to be 'pinky proof'. Even though things might seem cramped on the front panel the case does give me enough room for all the controls I want and lots of space inside for all the passive components.

Also going the IEC connector path for mains power in so no grommets or leads hanging an getting tangled out the back whenever it needs to be moved.

https://www.jaycar.com.au/encl-bench-88x279x304mm/p/HB5556

Marcel
10-11-2017, 09:14 AM
The topic of ESR meters was raised in this tread and thanks to a FB post I've found a modern supplier of what seem to be quite good meters from a UK manufacturer. They also make LCR meters and two versions of transistor testers and of all things UTP testers, all of which are handy bits of gear to have beside your multimeter if you have the need for them...

Manufacturer is... http://www.peakelec.co.uk/

Aussie distributor is ... http://www.altronics.com.au/peak/

DrNomis_44
10-11-2017, 10:18 AM
Yep, those Peak meters are great bits of test gear to buy if you're after test gear for amp servicing.

DrNomis_44
11-11-2017, 04:51 AM
Update:


My mate and I are going to see if we can grab the two fridges and washing machine from my old flat today, and while I'm there I'm also going to see if I can grab the Valve head and a small LCD TV that my mate gave me, I'm definitely going to be doing work on rebuilding the Valve head next year, starting possibly around February when I start ordering the necessary parts from Evatco.


Update 2:


Okay I've got the DIY Valve head with me at home in my new flat now, some of the green felt covering is crumbling away so I thought that it would be a cool idea to re-cover it in a Tweed Tolex style and add some Fender-style pot knobs, chrome corner protectors, and etc to it.

23194

DrNomis_44
13-11-2017, 11:22 AM
One thing I definitely need to do is re-do all the front panel labeling, some of the labeling is a bit askew and looks a bit of an eyesore, so it looks like I need to buy some new letraset sheets as well as all the necessary bits and pieces to get the amp re-built, should definitely turn out to be a fun project, I may even see if I can design a special dummy load that'll allow me to record the amp head straight into my DAW software, via the Audio Interface without disturbing my neighbors....silent recording in effect, there's an adjustable line out on the back panel, and I'm thinking of including a passive speaker emulator circuit of some sort so that the line-out signal can be fed to a P.A. system via a D.I. Box and it will sound like the amp is going through a speaker cab through the Front-Of-House P.A. speakers.

I don't know whether a passive Resistor-Capacitor circuit will work, or a passive Inductor-Capacitor circuit would work better, maybe Marcel might be able to help me out with that.

Marcel
13-11-2017, 04:12 PM
Hmmm, dummy load...

Do you remember those old jug elements that use a coil of wire around a porcelain block held in place by two brass rods.... 1500W jug element equates to about 40 ohms of resistance wire. In free air you can push up to about 50W into a unit trimmed back to 8 ohms. Dip that modified thing into a cup of water and the power rating jumps up to a 5minute @ 500W rating. Wilt a bit of forward thinking you could arrange to include 4+8+16 ohm taps.

I use a much larger ceramic 2x8 ohm free air unit rated at 100W continuous. RS and element 14 do sell 100W and 200W bolt down enclosed 4 or 8 or 16 ohm resistors for reasonable prices.

Most (though far less these days) electrical wholesalers have those replacement 1500W or 1200W elements.

As for inductance, you could add a 100uH coil in series to the resistive load, although strictly it is not needed. My ceramic resistance wire jig measures at 0.5uH and most guitar speakers are between 50uH and 100uH and so far I have never encountered an issue. When you calculate it out 100uH is a impedance of about 12 ohms at 20kHz but only 3 ohms a 5kHz and less than an ohm at 1kHz so at guitar frequencies they are significant but usually on the test bench they are not worth worrying about ... They are a huge worry on stereo hifi tube amps pushing large quantities of 20kHz...

Marcel
13-11-2017, 04:21 PM
Just read elsewhere that this amp build is to be based on a SLO-100... Is this true?... Do you have a circuit ?... Are you going to include clean/crunch to OD switching via a foot pedal ? ...

DrNomis_44
13-11-2017, 06:02 PM
Just read elsewhere that this amp build is to be based on a SLO-100... Is this true?... Do you have a circuit ?... Are you going to include clean/crunch to OD switching via a foot pedal ? ...


Yep, I've got the complete SLO 100 circuit, which includes the full two-channel preamp, power amp, power supply and footswitching circuitry, I got it as a pdf from the Sloclone.com website, and I'm going to be implementing the full footswitching system in my amp build too.


The only thing I'm going to be doing different is switching to EL34 power tubes, the circuit specifies 6L6 power tubes, so I'll probably get more of a British high-gain sound out of the amp.

And rather than use a set of four power tubes, I'm only going to be using two power tubes, there's a Triode/Pentode switch on the back panel of the amp which was something I added to the amp in a previous build, the Triode/Pentode switch basically re-configures the power tubes so that they can work either as Triodes, or Pentodes, the output-power drops to around half-power in Triode mode but that also changes the feel of the amp too, I thought it was cool enough to keep.


Interestingly enough, the SLO 100 footswitching circuitry included in the pdf is pretty simple, based on LDR/Led opto-isolators.


If you're interested in a copy of the pdf, here's where I downloaded it from:

http://diy-fever.com/wordpress/wp-content/uploads/2009/12/SLOCLONE-OFFICIAL-SCHEM.pdf

Marcel
13-11-2017, 07:06 PM
Thanks Doc... the circuit is very useful as the circuits I have are difficult to read hand drawn versions and don't include the wiring in the actual foot switch.

Initially I was only interested in how the switching was done so I could incorporate something similar in my AC18W build to swap from a 12AX7 input tube to the EF86 tube, but over the course of the afternoon I've been increasingly tempted to gut my 2204 build and step it up to a build not unlike yours as a 50W SLO-100 type build or more probably a 50W hot rod. As my 2204 build originally in a former life had 6L6's and the output transformer is impedance matched for 6L6's I'll probably pull the EL34's it's currently fitted with mostly as due to Z issues there have been moments where my 2204 is not happy with the load it get presented with. I have a Marshall with EL34's so some new tones will become available if I do make the swap in this build from EL34's to 6L6's...

Keeping the T/P switch is a good idea, If I go ahead then I'll probably keep the PPIMV control that is already in my 2204 build.

DrNomis_44
13-11-2017, 07:23 PM
Thanks Doc... the circuit is very useful as the circuits I have are difficult to read hand drawn versions and don't include the wiring in the actual foot switch.

Initially I was only interested in how the switching was done so I could incorporate something similar in my AC18W build to swap from a 12AX7 input tube to the EF86 tube, but over the course of the afternoon I've been increasingly tempted to gut my 2204 build and step it up to a build not unlike yours as a 50W SLO-100 type build or more probably a 50W hot rod. As my 2204 build originally in a former life had 6L6's and the output transformer is impedance matched for 6L6's I'll probably pull the EL34's it's currently fitted with mostly as due to Z issues there have been moments where my 2204 is not happy with the load it get presented with. I have a Marshall with EL34's so some new tones will become available if I do make the swap in this build from EL34's to 6L6's...

Keeping the T/P switch is a good idea, If I go ahead then I'll probably keep the PPIMV control that is already in my 2204 build.


Before I stripped all the original circuitry out of my amp, it was basically a Mesa/Boogie Mk I preamp circuit tacked onto a Marshall power amp circuit, what motivated me to strip all the circuitry out and re-build it as a Soldano SLO 50 was that, with the original circuitry, I was getting a reasonably good clean tone but the overdrive tone was very lackluster, no matter what I did with the tone controls, the tone of the amp didn't change much from a bassy tone that had a tendency to fart-out a bit when the gain was turned up too much, so, with the Soldano SLO circuitry I'm hoping that'll give me a good clean, crunch, and overdrive sounds, been checking out lots of SLO100 demos and I liked the sounds I was hearing.


It's interesting how in the Sloclone schematic, V2b is set up with a 39k cathode resistor, and a 100k anode resistor that's in parallel with a 1nF/630V DC cap, the 39k cathode resistor would set the biasing of that gain stage so it self-biases very close to cut-off if my valve theory is correct, I'm guessing that the 1nF cap in parallel with the 100k resistor helps to attenuate all the really high harmonics when V2b is overdriven, I'm guessing that V2b would be operating at very high gain due to the really low cathode to anode current so it would go into saturation and cut-off relatively easily.

Marcel
14-11-2017, 04:34 PM
There is a lot going on around both sides of V2. I like how your circuit includes notes whereas mine is mostly the same yet has no notes and quite a few nasty errors. I'm pretty sure yours has an error around the power transformer as I can't see one winding with lots of taps doing the needed job correctly, most likely it should be 3 windings...

Much of the Soldano circuit carries many similarities to both Fender and Marshall designs, but with a few modern and very useful tweaks. I just love how a change in value here or there can make all that difference....

DrNomis_44
14-11-2017, 04:58 PM
There is a lot going on around both sides of V2. I like how your circuit includes notes whereas mine is mostly the same yet has no notes and quite a few nasty errors. I'm pretty sure yours has an error around the power transformer as I can't see one winding with lots of taps doing the needed job correctly, most likely it should be 3 windings...

Much of the Soldano circuit carries many similarities to both Fender and Marshall designs, but with a few modern and very useful tweaks. I just love how a change in value here or there can make all that difference....


Yep, the circuit pdf I downloaded does include some very useful information, like for example the voltages on the cathodes and anodes of the preamp valves, definitely going to be useful in the event that you need to do any troubleshooting, the circuits are easy to follow and understand too, I think that the errors in the power supply may have been due to the limitations of the software used to create the circuit diagram more than anything else, I've also got a set of Turret Board layouts in pdf form for the Soldano circuits, but I may need to make some modifications to the layouts to enable them to work with the chassis i made for my amp, and in particular the power amp Turret Board layout, it was designed for 220uF/350V RB style Electrolytics, but I can only find some 220uF/350V RT style Electrolytics amongst Evatco's stock of caps, I've got two big Electrolytic caps installed on the chassis, they are dual 50uF Electrolytics rated at 500V DC, i want to include them in the power supply circuitry since removing them will leave a couple of big holes in the chassis.


The SLO 100 circuit looks like it borrows a few ideas from Mesa/Boogie and Peavey, I think Mesa/Boogie were one of the first companies to come up with the concept of gain-stage cascading, but Mesa/Boogie basically took a Fender circuit and added gain-stages to it and ended up with the Mk I circuit, it was around the early 80's when gutarists were taking their Marshall amps to amp repair techs to get them modded for extra gain in order to get overdrive sounds suitable for playing music in the then new genre of Thrash Metal, other amp manufacturers, like Peavey, followed suit, if you compare the preamp circuit of a Peavey 5150 with that of an SLO 100 and Mesa/Boogie Dual Rectifier, you'll notice some similarities, I reckon they borrow from each other.

Marcel
14-11-2017, 10:46 PM
Can't but love those drawings done on a CAD PC, so nice and clear and easy to read... it is just so sad that they often contain as many mistakes, errors or omissions as drawings done in pencil on a paper beer coaster ... suffering the use of either or both is part of the trade I guess ...

You're right Doc, they do all borrow from each other and we are just as guilty of it. One thing you don't see much of is inventive new ways to implement tubes... everything is common cathode bar for the two other and often identically copied by anyone and everyone versions of common anode (cathode follower) and common grid (2nd 1/2 of a PI) circuits. There is a lot of fiddling with bias but it is rare to see to see a "WTF!!" implementation doing something Wow! ... Maybe things were tried eons ago but have fallen into infamy due to lack of that 'Wow' thing becoming popular or most likely because 'transistors can do that' took its place...
But I lament, and I must shoot that melancholy in the foot.!!

In my hunt for more SLO-100 info I've stumbled on some old Peavy and Dumbel circuits... I'm still keen on a 6L6 finals amp, but now I'm hugely at odds as to which front end I should feed it with. Something my JVM210 doesn't do overly well is cleans, the AC18W is better yet it too has its own failings and for reasons I won't give here I want to avoid the typical Fender circuits so the search is on for a pedal friendly clean option that I can dirty or crunch up to taste.

Lol... Thrash Metal...lol .... My first, in I think it was '82 I had one guy in Melbourne ask me to 'hot modify' his 240VAC US version Fender Super Twin...The dude wanted "buckets of gain" and the amp also had to feed two Marshall Green back loaded quad boxes (essentially a full stack)... I was in the RAAF at the time so I did the mod at home, out with all the AT7's and in with a full fresh set of AX7's plus a few tweaks, and Damn that rig made some noise, so much that while I was testing it my landlord (and mentor in tube electronics) got complaints from neighbours 2 streets away but that could also have just been because of my mediocre playing into something so wicked in the OD department. Actually, thinking back, even when using my cheap Japanese plywood Ason strat of the time this Super Twin ended up at gain/vol setting of less than 4's for cleans and at 9's sounding very similar to a wound up OD2 in a modern JVM410.

Marcel
16-11-2017, 04:02 PM
A small step back for the topic... Dummy loads.

A shot of my 8ohm 100W + 8ohm 100W load, also has two 600ohm terminators for other audio stuff I play around with. If I feed it with 1kHz @ 100W you can just hear the coils singing as they use our planet Earth's magnetic field to push against. If I dunk the load in a bucket of clean (distilled) water the load will comfortably handle two 500W RMS channels (as in a big PA system or a big bass amp) although for a test of a few seconds at 500W RMS (to check for clipping or max power out) I usually don't bother with the drama of messing with water.

DrNomis_44
22-11-2017, 06:42 AM
I might see if my local Bunnings store has any of those electric kettle heater elements in stock, and if they do have them at a reasonable price I'll buy some so I can make a decent dummy load, in the meantime I'll have to make do with a 50 watt 8 Ohm dummy load that I scored from my local Uni some years ago.

Dummy loads are a very useful bit of test equipment when it comes to building amplifiers, in that you can run the amp at full power for testing purposes without blowing out your eardrums, or annoying your neighbors.

Might be a good basis for a future DIY project.


Update:


Just had a quick browse through Evatco's range of power transformers that they've got in stock and I think I have found the perfect one to replace the existing power transformer installed on the chassis of my Valve amp head, the Sloclone Schematic I'm using for my amp re-build specifies a power transformer with the following specs for a 50 Watt Sloclone amp:


Primary:

240V AC / 50Hz.

Secondary :

360-0-50-360 @ 200mA DC (HT and Bias Supply).

6.3V CT AC @ 6A (Power Tube Heater supply).

6.3V CT AC @ 2A (Preamp Tube Heater Supply).

And here are the following specs for the Evatco Power Transformer I have selected:

Primary:

240V AC / 50 Hz.

Secondary:

375-0-50-375 @ 201mA DC (HT and Bias Supply).

5V CT AC @ 2A (Rectifier Heater Supply).

6.3V CT AC @ 6A (Power Tube Heater Supply).

6.3V CT AC @ 6A (Preamp Tube Heater Supply).


I think this transformer is going to serve the purpose perfectly, it is listed as Evatco's 374bx Power Transformer, and costs $200.00 all up, which is fine for me, I've decided that I can re-use the existing output transformer, so I don't need to order a new one.

Here's a link to the webpage:

https://www.evatco.com.au/http://evatco.neto.com.au/http://evatco.neto.com.au/374ax


Since the amp uses four UF5408 Silicon Power Rectifier Diodes instead of a Rectifier Tube, I can use the spare 5V CT AC @ 2A Secondary to power the channel switching circuitry, I reckon it should work fine.


Evatco also seem to have a pretty good range of Metal Film resistors with power ratings from 1 Watt to 3 Watts, now since my Sloclone 50 amp is a high-gain amp, I'm going to elect to use Metal Film Resistors throughout the amp's circuitry, reason being is that Metal Film resistors don't generate anywhere near as much hiss-noise as traditional Carbon Composition resistors do, which is essential for low noise in a high-gain amp, I'm also going to try and over-rate the resistor for the job it does in the Sloclone amp's circuitry, by over-rate I mean ensure that the power dissipation capability is more than adequate, for example I would choose to use a 1 watt resistor when a 1/2 watt resistor is normally called for, this increases the reliability of the resistor and ensures that the amp is not going to break-down when I least want it to, incidentally, this is also why I elected to build the majority of the amp's circuitry on Turret Boards rather than some Etched PCBs, in the unlikely event that a resistor or other component fails, I can simply de-solder the faulty component and replace it with a new one without having to completely remove the board like you have to with an etched PCB, that's the main advantage with Turret Boards, ease of serviceability although it does mean more time is needed to build the amp and there's more likelihood of errors cropping up, but since this is a one-off build rather than multiple build, time taken to build the amp is a moot-point.


Each one of the 5 Preamp Tubes is a 12AX7/ECC83 type, the heaters of these can be powered two ways, either by 6.3V AC @ 300mA (Heater filaments in parallel), or 12.6V AC at 150mA (Heater filaments in series), I'm going to be powering them by 6.3V AC so the Heater filaments will be in parallel with each other, now since there are five 12AX7/ECC83 Tubes all up, the 6.3V AC Heater supply needs to supply 5 X 300mA, or a total of 1.5A if my maths is correct, this is about a quarter of the maximum supply current of one of the 6.3V AC @ 6A secondaries of the new power transformer so there's plenty in reserve.

Each of the two EL34 Power Tubes I'm going to be using requires a Heater supply of 6.3V AC @ 1.5A, which means a total supply current of 3A, this is half the maximum supply current that the other 6.3V AC @ 6A secondary is capable of, again plenty in reserve.


The only issue I can foresee is that the HT Voltage may end up a bit higher than noted in the Power Supply Schematic.


Note that the maximum supply current of a power transformer secondary winding is the maximum current that it can supply before the supply voltage starts to drop due to Ohm's Law, the power transformer will start to get warm but won't burn out unless a dead-short develops across the secondary winding for some reason, hopefully that won't happen provided it gets wired-up correctly.

DrNomis_44
05-12-2017, 12:58 PM
Update:

Went to Jaycar electronics today and bought a few new bits for the Sloclone 50 amp head, a couple of beefier toggle-switches to replace the current thin ones mounted next to the inputs on the front panel, a Green 3mm Led and a Blue 3mm Led for the channel indicators, two 1/4 inch sockets for the inputs, and nine new pointer-style knobs.


Here's a couple new pics of my Sloclone 50 amp, it has some new pointer knobs and toggle switches installed on the front panel:

23639

23640

DrNomis_44
15-12-2017, 12:45 PM
Update:

If anyone is interested, here's a link to the Sloclone Forum website, you may need to register as a member before checking out the various forum threads though, registration is free:

www.slocloneforums.com

Ik7
16-12-2017, 10:04 PM
Have you guys ever tried the Russian equivalent of the ecc83/12ax7? Or even their 6V6 or EL84 tubes? They can handle much higher plate voltages and sound incredible. I use them in my builds, the 12ax7 is easier to wire up too as pin 4 and 5 are heaters, and pin 9 is used on an internal shield.

The other good thing is they are cheap too, I paid £12 for 4 12ax7s and two EL84's.

DrNomis_44
20-12-2017, 08:53 PM
Have you guys ever tried the Russian equivalent of the ecc83/12ax7? Or even their 6V6 or EL84 tubes? They can handle much higher plate voltages and sound incredible. I use them in my builds, the 12ax7 is easier to wire up too as pin 4 and 5 are heaters, and pin 9 is used on an internal shield.

The other good thing is they are cheap too, I paid £12 for 4 12ax7s and two EL84's.


To be honest, I didn't even know that there was a Russian equivalent of the ECC83/12AX7, or the 6V6 and EL84, but I'm assuming that their electrical characteristics should be reasonably similar, if not the same, most of the valves available today are made either in China (Shugang), Yugoslavia, or in Russia (Sovtek), during the 50's and 60's, because Russia was a Communist nation, it was effectively shut-out of the Solid-State revolution happening in America, so it tended to rely quite heavily on valve technology so the majority of valve manufacturing plants tended to be in European and Asian parts of the world, although Britain and America had valve manufacturing plants too.

Marcel
21-12-2017, 06:29 AM
Philips also had tube manufacturing in many place with the biggest in the Netherlands and Germany, They also had two plants in Australia being one in Sydney and another in Melbourne... At one time there was also four TV & radiogram building factories within walking distance of the Melbourne tube factory...

Alas, all are long gone...

Marcel
16-02-2018, 10:24 PM
What too much coffee does to an amp builder..... lol

https://www.youtube.com/watch?v=9r46NASb-3w

DrNomis_44
18-02-2018, 03:38 PM
Yep, too much of that stuff will do it....lol.

DrNomis_44
01-03-2018, 03:30 PM
Update:


I went to my local Officeworks shop today to buy a few things I needed, while I was there I also bought a 128 page book of 5mm graph paper, there's a good reason why I bought it, it's for designing my own Turret Board layouts, I've never tried designing a turret Board layout so I thought that I would have a go at it as part of the build-process for the amp, I've already got a set of layouts in PDF form but there's a slight problem, the Turret Board insulation material that I'm going to order from Evatco is smaller in size compared to the pdf layouts, so I need to do some re-designing....no drama though.

25144


Usually on a Turret Board, the Turrets are placed about 10mm apart, using graph paper to design a layout will help to keep the Turrets in a straight line.

DrNomis_44
16-03-2018, 02:21 PM
It's a bit of a quiet and rainy day at home today, so I thought that it would be a good excuse to do some work on getting things organized with regards to the parts and bits and pieces needed to complete my Sloclone 50 amp head rebuild, to start off, I'm in the process of evaluating how many sheets of blank fibreglass turret board, and turrets I'll need to order from Evatco to make the turret boards for the amp, Evatco stock two different thickness of blank fibreglass turret boards, a 2mm thick board and a 3mm thick board, you can order them as a 300mm by 60mm sheet, or a 300mm by 80mm sheet, I'm going with the 2mm by 300mm by 80mm sheets because they are closest in dimension to the specifications in the pdf layouts I'm working with, the only issue is that the length is a bit short but I'm going to get round that by building the majority of the preamp circuitry on one 300mm by 80mm board, and then build the phase-splitter circuitry on a shorter board, hence the reason why I need to work out how many 2mm by 300mm by 80mm sheets I need to order, also, I decided to go with the 2mm sheets because that will make it easier for me to cut them to length.

The reasons why I chose to use turret boards rather than etch a PCB is as follows:

1, I'm currently not set up to etch my own PCBs.

2, I've never tried making a turret board before, and this project seemed like as good an excuse as any.

3, A turret board is much easier to service when it comes to replacing faulty components, you simply de-solder them from their turrets (have you ever noticed how frustrating it can be to replace a faulty component on an etched PCB?, you have to completely remove it from the amp chassis to replace the part, then re-install it to perform tests on the amp).

What I've done so far is to cut a couple of pieces of cardboard roughly to 300mm by 80mm and a couple more to 150mm by 80mm (these will represent the phase-splitter and power supply boards), and then I'm going to use the pieces of cardboard to do a test-fit evaluation to see how it's all going to work out with regards to turret board positioning in the amp chassis, might see if I can take a pic or two so you can see how they are going to be arranged.


Here's a pic of how the turret boards are going to be roughly arranged, although I may need to tweak it a bit later on, this does seem to work though:

25474


It looks like I'll need to order a minimum of two 2mm by 300mm by 80mm blank fibreglass turret boards, but I'll increase the quantity to four, that way if I somehow make a mistake on one of the boards (lets face it, in the real world nothing ever goes exactly to plan according to Murphy's Law), I can simply cut a new piece and start again, hopefully I'll get it right the first time.


In the above pic the piece of cardboard labeled "Preamp" represents the turret board with the majority of the preamp circuit on it, likewise, the piece of cardboard labeled "Phase Splitter" represents the phase-splitter turret board, and the piece of cardboard labeled "Power Supply" represents the power supply turret board.

Marcel
16-03-2018, 05:23 PM
The only spanner flying through the air with your design method Doc is the spacing of the turrets on the boards from Evacto. If you have included that on your cardboard cut outs then all is sweet, if not then Murphy is still possibly in the mix...

DrNomis_44
17-03-2018, 01:05 AM
The only spanner flying through the air with your design method Doc is the spacing of the turrets on the boards from Evacto. If you have included that on your cardboard cut outs then all is sweet, if not then Murphy is still possibly in the mix...


Good point, I was assuming that the turrets are spaced 3/8 inch, or 10mm apart from each other (I think that's the standard spacing), the graph paper I'm using to create the layouts is 5mm square, so, if I space the turrets out every two 5mm squares, then it should be fine, hopefully Murphy doesn't throw a spanner in the works.


One thing though, when we make assumptions we leave ourselves wide open to mistakes being made.

DrNomis_44
22-06-2018, 03:25 PM
Update:

Rightio, time for an update.....


Just been working on making up a layout for one of the Turret boards for the amp I'm in the process of building, anyway, as it turns out a 300mm by 80mm piece of F4 fibreglass board is going to be too small to accommodate most of the preamp circuitry, Evatco sells sheets of F4 fibreglass board material in either 300mm by 60mm, or 300mm by 80mm, in 2mm or 3mm thickness, so, rather than follow the layout I'm working from verbatim, I'm going to have to get a bit creative, and I think I've figured out a solution, I'll need to do some experimenting to be sure though.

DrNomis_44
02-08-2018, 02:55 PM
Update:

Been seriously thinking of switching from two EL34 power tubes to two 6L6 power tubes, I think the Soldano SLO 100 originally came from the factory with four 5881 power tubes, but I could be wrong, the 5881 has the same internal electrode design as the 6L6.

Marcel
02-08-2018, 04:57 PM
Swapped the EL34's for a pair of 6L6's in my 2204 build... I figured as it was originally built with 6BQ5's, and modified to 6L6's before I got it then it would probably be a good fit.

While now with the 6L6's the output impedance selector works correctly the output volume level is noticeably reduced. With the EL34's there was a lot more volume and "grunt" from the amp but the impedance selector needed to be in the next position for the amp to 'behave'. That's not to say the 6L6's are weak, hell no, they do kick out substantial clean volume, maybe I'm just noticing the absence of 'dirt'... As HT volts, biasing, output transformer ratios and drive signal size all play important parts I'm guessing the build went from a solid and gritty 50W to a (for the moment) squeaky clean 40W...

I can't call it a 2204 build any more so its new name after it gets the EF86 input stage upgrade is the 6682 build... It will be interesting to hear how clean things get before further rounds of modifications to 'beef it up' again...

DrNomis_44
02-08-2018, 05:20 PM
Swapped the EL34's for a pair of 6L6's in my 2204 build... I figured as it was originally built with 6BQ5's, and modified to 6L6's before I got it then it would probably be a good fit.

While now with the 6L6's the output impedance selector works correctly the output volume level is noticeably reduced. With the EL34's there was a lot more volume and "grunt" from the amp but the impedance selector needed to be in the next position for the amp to 'behave'. That's not to say the 6L6's are weak, hell no, they do kick out substantial clean volume, maybe I'm just noticing the absence of 'dirt'... As HT volts, biasing, output transformer ratios and drive signal size all play important parts I'm guessing the build went from a solid and gritty 50W to a (for the moment) squeaky clean 40W...

I can't call it a 2204 build any more so its new name after it gets the EF86 input stage upgrade is the 6682 build... It will be interesting to hear how clean things get before further rounds of modifications to 'beef it up' again...


Did you use the same output transformer you had in it when you swapped the stock tubes for 6L6s?, if so, that might account for the perceived loss in output level, since the plate load for an EL34 is different to what the plate load for 6L6, that's probably why the impedance selector worked properly with the 6L6 tubes.

Marcel
02-08-2018, 06:38 PM
Yep, same transformer... Tough they sounded fine it was impedance issues with the EL34's that gave the main reason for switching back to 6L6's...

DrNomis_44
02-08-2018, 07:30 PM
Yep, same transformer... Tough they sounded fine it was impedance issues with the EL34's that gave the main reason for switching back to 6L6's...


Ah okay, yeah that would do it, power tubes are more picky about the load impedance they're working with than solid-state devices.

DrNomis_44
19-04-2023, 10:04 PM
Update:


Thought it was about time I did an update on this thread, okay, so earlier today I ordered some things from Evatco, a new Accutronics reverb tank for my Marshall MA 100C amp, two Bourns 500k A 24mm pots, two stereo Cliff Jacks (for my Fender Super Twin amp), and ten 28X2 tagstrip boards which I will be using to mount all the components in my SLO-50 amp build, I'm going to be calling the amp the Sloclone 50.

Here's what the tagboards look like:

https://www.evatco.com.au/tag-strip-28-x-2


I've elected to use these 28 X 2 tagboards because it looks to me the simplest way to build the circuits, you just solder the resistors and caps between two adjacent tags, and link the tags together where they need to be linked, of course I'll need to work out a suitable layout of the components on the boards beforehand, using some 5mm square graph paper, but at least I won't need to buy any special tools, the insulation on those 28 X 2 tagboards looks to be FR-$ Fibreglass similar to that used to make printed circuit boards, so the dielectric strength should be fine, the highest voltage in the amp is most likely going to be about 498V DC on the centre-tap of the output transformer, with about 384V DC going to the majority of the preamp and phase-splitter circuitry.

Dielectric-strength is basically a measure of how many volts that a piece of insulation material can withstand before it suffers an insulation-breakdown and leaks DC which is particularly important in valve amplifiers where the anti-phase outputs from the phase inverter are coupled to the grids of the power valves with high-voltage non-polarized caps, typically something like the pair of 22nF (.022uF)/630V DC caps that you find in Marshall amps like the Superlead Plexi, you want the dielectric, or insulator in the cap to block DC and pass only AC, because any DC leakage to the grids of the power valves will upset the biasing and cause the power valves to conduct too much current, when that happens the power valves can start to red-plate and glow cherry red or orange, or in some cases, the plate can literally melt because it is only made from thin metal sheeting and too much current makes it heat up very hot, that's one way to destroy a power valve.


Here's a question for you, Marcel, on the Evatco website they say that the Gold Lion KT-77 Power Valve that they sell is a drop-in replacement for an EL34 or 6CA7, my valve amp head build uses an output transformer designed for two EL34 power valves, if I put two of those Gold Lion KT-77 valves in the sockets will the output transformer work fine with them or would I need to swap it out for one designed for KT-77 power valves? I'm assuming that the existing output transformer should work fine.

Here's the Gold Lion KT-77 page on the Evatco website:

https://www.evatco.com.au/genalex-gold-lion-kt77

DrNomis_44
20-04-2023, 10:16 PM
Update:


Just found out that Evatco do stock the optocouplers I need to implement the channel switching, so, I'm going to go with the original optocoupler channel switching system rather than use relays.

DrNomis_44
21-04-2023, 10:32 AM
Update:


Just got a parcel from Evatco delivered a few minutes ago, inside it were a new Accutronics reverb tank I had ordered for my Marshall MA100c amp, two Bourns 500kA 25mm pots, two stereo Cliff Jacks, and ten of these 28 X 2 Tagboards I ordered for my diy scratch-build Soldano SLO 50 Sloclone 50 amp build, these will be used for mounting all the parts in the amp.

44206

DrNomis_44
27-04-2023, 09:25 AM
What was the rough cost of parts Doc?


Just did a quick re-assessment of how much the amp parts have cost me so far, and for a rough estimate I've probably spent less than Au$1,000.00 on it so far, mostly because some of the parts I didn't actually pay any money for, like the 2mm Aluminium sheeting I used to make the chassis, I scrounged the iron for the power transformer from an old movie projector, or a reel-to-reel tape recorder, my memory is a bit rusty, the only parts I had to buy were the 50W output transformer, which cost me something like Au$350.00 or so, maybe a bit more, plus the various resistors and etc, a friend of mine gave me two LCR dual 50uF/500V caps for nothing, I wished I had kept records of what parts I did buy so I could make a more accurate assessment.

DrNomis_44
04-05-2023, 06:40 PM
Update:

Managed to get my HP Officejet printer working again, and found some spare A4 printer paper, so, I went and printed-out all the Sloclone schematics and Turret Board layouts I have collected, tomorrow I'm going to start working on making some layout diagrams for the 28 X 2 Tagboards I'll be using to mount all the components, after that, I'll start prep-work on the tagboards so they will be ready for populating with components.

DrNomis_44
05-05-2023, 04:50 PM
Update:

I was just doing some searching on google for how to make an 8 Ohm/100W Dummy Load using some 5W Ceramic resistors, and found this useful webpage, so I thought I would post a link to it here just in case other forum might be interested, anyway, here it is:

https://www.omnicalculator.com/physics/parallel-resistor


As it turns out, by my calculations if I put a total of ten 82 Ohm/5W Ceramic Power Resistors in parallel with each other, that will give me an 8.2 Ohm/50W Dummy Load resistor, so, maybe if I double the value of all the resistors, and put twenty of them in parallel, that'll get me closer to what I want.

So, 2 X 82 gives us a total of 164.


Now, here's my thinking, if we put ten 164 Ohm/5W ceramic power resistors in parallel with each other, we effectively get a 16 Ohm/50W Dummy Load, and, if we put two 16Ohm/50W Dummy Loads in parallel with each other, we effectively get.......an 8 Ohm/100W Dummy Load.

The question is, are 164 Ohm/5W Ceramic Power Resistors available? most likely not, I'll consult my Jaycar Electronics Catalogue to find out.

Turns Jaycar don't stock a 164 Ohm/5W Ceramic Power Resistor, the closest next value up that they do stock is a 180 Ohm/5W Ceramic Power Resistor, Cat. No. RR3280.

So, how close can we get to 8 Ohms with a resistor value of 180? let's see.....

If we put ten 180 Ohm/5W resistors in parallel with each other we get an 18 Ohm/50W Dummy Load.

If we put two 18 Ohm/50 W Dummy Loads in Parallel we get.....a 9 Ohm/100W Dummy Load.

This is one Ohm larger than we need, but, we didn't take into account the resistor tolerance, or how much +/- of the marked value the resistor/s actually measured, and we also didn't take into account the very small resistance of the solder leads either.

Trevor Davies
06-05-2023, 08:10 AM
What is more important - the 8 ohm or the 100 W?

If you have two 18 ohms/50 W in parallel with an 82 ohm/5 W you can get 8.1 ohm /105 W? Is that allowed?

DrNomis_44
06-05-2023, 09:23 AM
What is more important - the 8 ohm or the 100 W?

If you have two 18 ohms/50 W in parallel with an 82 ohm/5 W you can get 8.1 ohm /105 W? Is that allowed?

Yep, that'll work because the power dissipation will be divided between all the resistors.


The 8 Ohms is important because that's the load the amp wants to see in order for the power amp circuitry to operate properly, as long as the power dissipation of the Dummy Load is more than what the amp will put-out there won't be any risk of burning out the load.

ian_macpherson
06-05-2023, 01:33 PM
Or you could use 11 180 ohm resistors rather than 10, which would give yo 16.4 ohms, or 8.2 for 2 sets in parallel.

DrNomis_44
06-05-2023, 04:28 PM
Or you could use 11 180 ohm resistors rather than 10, which would give yo 16.4 ohms, or 8.2 for 2 sets in parallel.


Yes, you're absolutely right, and that's something I didn't even consider doing, as long as the Dummy Load is close-enough to 8 Ohms it should work fine, so, if we put eleven 180 Ohm/5W Ceramic power resistors in parallel, that gives us a 16.4 Ohm 55W Dummy Load, and if we put two 16.4 Ohm 55W Dummy Loads in parallel, we get an 8.2 Ohm/110W Dummy load which is perfect for what I want to use it for, basically as a dummy load for when it comes to setting the bias of the two KT 77 power tubes prior to test-out to see if it all behaves correctly, without disturbing my neighbours, I'm sure they won't appreciate having to put-up with hearing a 1kHz Sine Wave at say 110dB.

So, it looks like I'm going to be ordering X22 180 Ohm/5W Ceramic Power Resistors online from Jaycar, or maybe Mouser Electronics soon.


Maybe I should start a new thread in the Pitbull Guitars Amplifier section for building Dummy Loads for guitar amps? I'm sure lots of forum members would find it a handy device to make.

DrNomis_44
11-05-2023, 04:29 PM
Update:

Just started work on making all the tagboards for mounting the components this afternoon.

DrNomis_44
30-05-2023, 05:59 PM
Update:


Popped-by my local Jaycar Electronics store to buy most of the resistors I will need to build all the circuitry in my diy scratch-build Sloclone 50 amp, there are some resistor values I needed which Jaycar did not have in stock, so I will be ordering them, and all the caps and etc online from Evatco, and another online Electronics Components supplier, it's going to be a real fun ride this year, hopefully my build will sound similar to this Soldano SLO 100 amp:

https://www.youtube.com/watch?v=hhgVQTRB9k8&ab_channel=HollywoodRareGuitars

DrNomis_44
03-06-2023, 02:07 PM
Update:

I stripped the Sloclone 50 chassis down so it was just a bare chassis and spray-painted the front and rear panels with some matt-white spraypaint I bought from my local Bunnings store, then I left it to dry overnight, today I went through the process of re-labeling all the controls and etc on the front/rear panels with some white paper dymo labelmaker tape, once I was satisfied that everything was good, I gave the front/rear panels two coats of satin clear-coat, also bought from Bunnings, seems to look pretty good so far, I'll see if I can post some pics later on for you to check out.....stay tuned.....

Here we go, this is what the front and rear panels look like now after I spraypainted them matt white and did all the re-labelling:

The Front:

44366

And the Back:

44367

DrNomis_44
05-06-2023, 02:10 PM
Update:


The progress on my diy scratch-build Soldano SLO-50 valve guitar amplifier seems to be going really well, today I managed to get all the resistors soldered onto the two main Tagboards containing the majority of the preamp and power amp circuitry, all I need to do now is order some parts online such as the new HV Electrolytic caps, all the new Tone and coupling caps, Optocouplers, and Cliff Jacks, I'm also going to order a new 3-way Impedance switch while I'm at it, and anything else I need, but for now, here's a pic of the two Tagboards with the resistors all soldered in place, there are wire links on the underside linking resistors where necessary:

44369

DrNomis_44
05-06-2023, 04:00 PM
Thanks Doc... the circuit is very useful as the circuits I have are difficult to read hand drawn versions and don't include the wiring in the actual foot switch.

Initially I was only interested in how the switching was done so I could incorporate something similar in my AC18W build to swap from a 12AX7 input tube to the EF86 tube, but over the course of the afternoon I've been increasingly tempted to gut my 2204 build and step it up to a build not unlike yours as a 50W SLO-100 type build or more probably a 50W hot rod. As my 2204 build originally in a former life had 6L6's and the output transformer is impedance matched for 6L6's I'll probably pull the EL34's it's currently fitted with mostly as due to Z issues there have been moments where my 2204 is not happy with the load it get presented with. I have a Marshall with EL34's so some new tones will become available if I do make the swap in this build from EL34's to 6L6's...

Keeping the T/P switch is a good idea, If I go ahead then I'll probably keep the PPIMV control that is already in my 2204 build.

I've definitely decided to keep the T/P switch but I relabelled it so that in T or Triode it is labelled 25W, and in P or Pentode mode it is labelled 50W, I also re-labelled the Depth control to Resonance, I've also decided to switch the power tubes to a matched pair of JJ KT-77 tubes, from what I read on the Evatco website KT-77 tubes are a drop-in replacement for the EL-34 with a bit more power handling/headroom, and a tone that's a cross between an EL-34 and a 6L6, I'm also going to try a set of five JJ 12AX7/ECC83 twin triodes, I made a very simple mod to the tonestack where I can switch between a 33k slope resistor and a 47k slope resistor using a panel-mount DPDT toggle switch I labelled Mids, I used an app called Duncan Amps Tonestack Calculator (you might know about it) and I generated a frequency spectrum plot of the tonestack with the two different slope resistor values, from comparing the two spectrum plots, I noticed a shift in the midrange notch between the two resistor values, so I thought that would be an interesting feature to have.


I've figured-out how to wire the T/P switch so that it switches one end of the 1k screen-grid resistors from pin-3 of the power valve octal sockets for the Triode/25W setting, and the common screen supply voltage node on the power supply circuit for the Pentode/50W setting, the other end of the two 1k screen resistors connect to pin-4 of their respective power valve octal sockets.

DrNomis_44
05-06-2023, 04:46 PM
While looking through Evatco's range of capacitors, I saw that they had every value of Cap I needed in 500V silver micas except 470pF, but, they did stock a 500pF/500V silver mica, which I'm going to use as a substitute for 470pF, there's only a difference of 30pF in value which I think is not worth worrying about, I was hoping to buy all the other cap values I needed in 630V yellow tubular RT style caps but they don't seem to stock any .022uF/630V ones, they do however stock .022uF/500V Blue Molded Sozo brand caps in stock that look like these:

https://www.evatco.com.au/sozo-500v-capacitors

They are a little pricey but I'm not worried, they seem to be very good quality caps, actually I've heard lots of good things about Sozo caps, never tried them before so this scratch-build amp project is a good excuse to do so.

Evatco don't seem to stock any 200uF/350V multi cap cans, but I did find another online company that sells 200uF/500V multi cap cans, I need two for this scratch-build project, so I'll order a couple of them.

DrNomis_44
06-06-2023, 11:24 AM
Update:

Today, I'm in the process of making a couple more Tagboards for my diy scratch-build Soldano SLO-50 guitar amp, one of the tagboards is for generating the -V Bias supply for the two KT-77 power tubes, they will not operate correctly in the amp without it, the other tagboard is for generating the +V High Voltage supplies for all the preamp and power tubes, again, the amp will not operate correctly without it.

DrNomis_44
11-06-2023, 06:57 PM
Update:

Just a quick update so you can see where I'm at in the build progress, I finished making all the tagboards I needed to make in order to mount all the components needed to make the amplifier work, here's a pic showing all the tagboards mounted in the amp chassis, all that's left to do is to finish populating them with parts, mounting the new transformers and etc that I need to order, and then do all the final wiring-up before doing the initial bias adjustment and tests to see if everything is operating correctly, and then comes the fun part, testing it out with my Ashton Quad Box and a guitar.

44382

Trevor Davies
12-06-2023, 05:58 PM
Looks very neat!

DrNomis_44
13-06-2023, 06:54 AM
Looks very neat!

Cheers, much appreciated!!!

DrNomis_44
15-06-2023, 10:18 AM
Update:


Some more parts I ordered from Evatco just arrived in the post, the black caps are F&Ts, blue caps are Sprague Atoms:

44398

Simon Barden
24-06-2023, 04:14 PM
Any more thoughts on making a load bank? Don’t forget that if you put them in an enclosure you’ll need to have a lot of ventilation for them as they will get pretty hot. And unless they are being screwed to a heat sink, then they will need to be mounted away from any backboard/PCB for better heat dissipation.

9 ohms won’t make a difference compared to 8 ohms. A speaker impedance will be less at some frequencies and higher at others. If you want 8 ohms, just add some more resistors in parallel.

I’d certainly have more power capacity in the resistors than you need. I don’t know how close to its limit a 5W resistor passing 5W is, but if you give it more power when setting up the amp, then you could get a succession of blown resistors and no load bank, and power tube and output transformer damage following.

Of course you don’t need to bias the amp at full power with a signal going through it at all. Just use the speaker and don’t have anything plugged in the input.

DrNomis_44
25-06-2023, 03:05 PM
Any more thoughts on making a load bank? Don’t forget that if you put them in an enclosure you’ll need to have a lot of ventilation for them as they will get pretty hot. And unless they are being screwed to a heat sink, then they will need to be mounted away from any backboard/PCB for better heat dissipation.

9 ohms won’t make a difference compared to 8 ohms. A speaker impedance will be less at some frequencies and higher at others. If you want 8 ohms, just add some more resistors in parallel.

I’d certainly have more power capacity in the resistors than you need. I don’t know how close to its limit a 5W resistor passing 5W is, but if you give it more power when setting up the amp, then you could get a succession of blown resistors and no load bank, and power tube and output transformer damage following.

Of course you don’t need to bias the amp at full power with a signal going through it at all. Just use the speaker and don’t have anything plugged in the input.



Yep, I'm going to use the same type of metal enclosure as I used for my XR2206 Function Generator, it does have some good ventilation, and I'm also going to include a small 12V DC powered fan as used in some computer cases to add some extra cooling, with the help of another forum member, I came up with a suitable design for the Dummy Load that uses a total of X22 180 Ohm/5W ceramic resistors in parallel to give an 8.2 Ohm/110W Dummy Load, that should be more than enough for testing purposes.

Here's a link to the Dummy Load project thread I started:

https://www.buildyourownguitar.com.au/forum/showthread.php?t=12363


Note that the basic design I came up with can be easily modded to suit the requirements of those wanting to build one for themselves.

DrNomis_44
30-06-2023, 11:16 AM
Update:

Thought I would post some more pics of the insides of my diy scratch-build Sloclone 50 amplifier, so here we go:

44481

44482

44483

DrNomis_44
03-07-2023, 03:12 PM
Update:


Just got these in the mail this afternoon, they are a couple of Dual 200uF/500V Can Caps I ordered recently from SoundLabs Group.com, I was a bit concerned that their diameter would be smaller than the two original blue LCR dual 50uF/500V can caps I had installed in the chassis, but turns out these are the same exact diameter as the LCRs, so, that means I can re-use the original chassis mounting-bracket hardware and I don't need to go to the trouble of ordering new mounting brackets.

Here's a pic of the new can caps:

44502

Simon Barden
03-07-2023, 03:29 PM
I’d guess that the dual cap cans are pretty much a standard size. You can always fit smaller caps in a bigger enclosure, but not the reverse, so it pays the manufacturer to standardise on one or two enclosure sizes for this type of multiple cap.

DrNomis_44
03-07-2023, 03:57 PM
I’d guess that the dual cap cans are pretty much a standard size. You can always fit smaller caps in a bigger enclosure, but not the reverse, so it pays the manufacturer to standardise on one or two enclosure sizes for this type of multiple cap.


My thoughts exactly, but it's a real bonus that I don't have to order a couple of new chassis mounting brackets, I can re-use the existing ones which are still perfectly good.


My understanding is that the can itself is tied/connected to the - terminal of each of the capacitors in the can, since the two can caps will be wired in series, that means one of them will have it's - terminal floating/sitting at half the total + HT voltage, I'm not sure what the voltage-rating of the plastic shrink-film covering each of the can caps is, so I'm going to use some heatshrink tubing to ensure that each can cap is fully insulated from the chassis.

Last thing I want is for the chassis to be sitting at something like 200 or 300V DC, when it is supposed to be at ground potential.

The worst electric shock I've ever experienced in my life was from a Wimshurst machine that was being demonstrated in science class when I was in high school, must have been something like 10,000 volts but didn't it ever make me jump, so glad I lived to tell the tale.

Simon Barden
03-07-2023, 04:44 PM
I don’t know if the can contains 2x 500v capacitors or 2 x 250v capacitors to give a 500v rating.

I’ve just looked at a schematic for a DIY SLO 50 , and that shows 2 x 300v capacitors, with a DC reading of 498v coming off them.

2 x 500v caps internally is fine, but 2 x 250v isn’t.

Any idea? I’ve had a quick look around and haven’t found an answer yet.

DrNomis_44
03-07-2023, 06:05 PM
I don’t know if the can contains 2x 500v capacitors or 2 x 250v capacitors to give a 500v rating.

I’ve just looked at a schematic for a DIY SLO 50 , and that shows 2 x 300v capacitors, with a DC reading of 498v coming off them.

2 x 500v caps internally is fine, but 2 x 250v isn’t.

Any idea? I’ve had a quick look around and haven’t found an answer yet.


Well, my understanding is that in a dual 200uF/500V can cap, the two 200uF/500V caps share a common - terminal, so, that basically means that each of the two 200uF caps both have a maximum working voltage of 500V, if you wire them in parallel by joining the two separate + terminals together, you effectively create a single 400uF/500V capacitor, and if you wire two separate 400uF/500V capacitors in series you effectively get a capacitor that's half the capacitance value, but double the voltage-rating of a single 400uF/500V cap, or a single 200uF/1,000V cap, this is something Marshall used to do in their JTM45 amps and Super Lead Plexi amps, Fender also used to do that too in their Twin Reverb amps, it's also common practice to solder-in a bleeder resistor in parallel with each can cap to equalize the voltage as well as bleed-off the charge when the amp is powered-down.

Here's a diagram I drew showing how the two 200uF/500V caps are connected internally in the can:

44503


So, if you connect two 400uF/500V caps in series and connect the -terminal to circuit ground, and the remaining + terminal to the +HT supply like this with the two 220k/1W voltage equalizing resistors, each capacitor should have about half the +HT voltage on them:

44504


I've just been looking through Evatco's range of power transformers, and I think I have found the ideal power transformer for my amp project, the power transformer I was going to use has an HT secondary rated for 375-0-50-375 V AC @ 201mA, my main concern is that if I use this transformer some of the supply filter caps in the power supply may be over-voltaged, the new power transformer I found has an HT secondary rated for 350-0-50-350 V AC @ 201mA, 350V AC is only 10 volts less than what's specified in the schematics I'm working from, they specify a power transformer with an HT secondary rated to put out 360-0-50-360 V AC @ 200mA, so, I think the new power transformer I found is a good compromise, here's a link to it, I think the heater secondaries should be adequate enough to power all the valve heaters, as well as the footswitching circuitry:

https://www.evatco.com.au/373bx-power-transformer

Simon Barden
03-07-2023, 09:14 PM
Yes, if they are internally connected like that and you feed one multi-cap into the other (with the balancing resistor connection in the middle), then that's fine.

I was looking at a circuit digram and seeing one capacitor above another, had the mental picture of that's how the two capacitors were arranged in the common can. But its the side by side caps that are the common can, with one can connected to another/feeding into the other.

44505

Yes, you then get about 250v across each capacitor, so a 500v rating is perfectly safe (providing the resistors don't loose their ground connection or a cap doesn't go short circuit - but you can't allow for every possible failure scenario).

With the way you've drawn it, it makes much more sense to me.

Thanks.

DrNomis_44
03-07-2023, 09:28 PM
Yes, if they are internally connected like that and you feed one multi-cap into the other (with the balancing resistor connection in the middle), then that's fine.

I was looking at a circuit digram and seeing one capacitor above another, had the mental picture of that's how the two capacitors were arranged in the common can. But its the side by side caps that are the common can, with one can connected to another/feeding into the other.

44505

Yes, you then get about 250v across each capacitor, so a 500v rating is perfectly safe (providing the resistors don't loose their ground connection or a cap doesn't go short circuit - but you can't allow for every possible failure scenario).

With the way you've drawn it, it makes much more sense to me.

Thanks.

No worries, I have to admit that it took me a while to get my head around it too.


The thing I'm most concerned about is putting too much voltage on the single 47uF cap and the two 10uF caps in the power supply circuit in my build, I'm using a black F&T 47uF/500V Axial and two blue Sprague Atom 10uF/500V Axial caps in my build, if I go with the transformer with the 375-0-50-375 V AC @201mA secondary the main +HT voltage is definitely going to be higher than 498V DC, I'm estimating probably something like 560V DC, which could over-voltage some caps in the power supply.


I'm using two more black F&T 47uF/500V caps in the -50V Bias supply, which is probably overkill for the job, but at least it means that the -V Bias supply should be rock-solid reliable, which I think is important because you don't want your expensive power valves going horribly into red-plating because the -V Bias supply failed completely.

Simon Barden
03-07-2023, 10:30 PM
Not only the caps, but also the valves! The maximum plate voltage for a 6L6GC in pentode mode is 500V. The SLO 50's design 495V is already pushing the valves to the limits, and you need to allow for supply voltage variations. I'd definitely go with the 350-0-50-350 transformer. It's fractons of a decibel less output volume and its safer.

DrNomis_44
03-07-2023, 11:10 PM
Not only the caps, but also the valves! The maximum plate voltage for a 6L6GC in pentode mode is 500V. The SLO 50's design 495V is already pushing the valves to the limits, and you need to allow for supply voltage variations. I'd definitely go with the 350-0-50-350 transformer. It's fractons of a decibel less output volume and its safer.


I elected to go with a set of two matched JJ KT-77 power valves in my amp build, on the Evatco website they say that the KT-77 is a drop-in replacement for the EL-34, I compared the pin connections on the EL-34 datasheet with the ones on the KT-77 datasheet and they are virtually identical except for pin 1, which is unused in the KT-77 but is connected to the suppressor grid in the EL-34, whereas in the KT-77 the suppressor is internally connected to the cathode, in the JJ KT-77 datasheet it says that the maximum Anode/Plate voltage is 800V, for a JJ EL34 it says the maximum Anode/Plate voltage is 800V, or I may be totally wrong about that, but you're absolutely right, I'm no expert but I would say 500V in each case is a more realistic limit, at higher voltages there's more of a risk of arcing between adjacent pins on a valve socket, something that caused my Marshall MA100C amp to blow the HT fuse all the time, turned-out it was because the factory-installed power transformer was rated for 230V AC mains supply, not our Australian 240V AC mains supply, so the resulting +HT supply was higher than it was supposed to be, at least one of the factory installed Marshall EL34 valves suffered an arc between two pins, one other EL34 valve red-plated, and I think the remaining two were okay, cost me quite a bit to get it fixed so the amp wouldn't blow HT fuses all the time, think it was something like Au$800.00 or so, and I paid Au$1,300.00 or so when I bought the amp brand-new.

Simon Barden
03-07-2023, 11:35 PM
EU/UK mains voltages are a nominal 230v, but that's with a ±10% tolerance, so 207v to 253v AC. This split the difference between the UKs 240v and Europe's 220v and pushed the big switch from linear to switched mode power supplies that could accept a wide range of voltage inputs.

But whilst new build offices and factories etc in the UK have transformers for the buildings set to 230v, a lot of the UK is still at a nominal 240v, so there shouldn't be any problems with 230v transformers running at 240v or there would be a lot of irate British customers!

Sounds like there might have been some other issues with the design of that amp as it's not something I've come across here. Possibly the factory buyer ordering some below-spec valve sockets because they were considerably cheaper without understanding the implications.

Very high plate voltages mean low current draw and apparently a lot more crossover distortion, so the plate voltage is normally kept lower, in the 400v region (unless you really want more power out of the valve at the expense of fidelity).

DrNomis_44
03-07-2023, 11:50 PM
EU/UK mains voltages are a nominal 230v, but that's with a ±10% tolerance, so 207v to 253v AC. This split the difference between the UKs 240v and Europe's 220v and pushed the big switch from linear to switched mode power supplies that could accept a wide range of voltage inputs.

But whilst new build offices and factories etc in the UK have transformers for the buildings set to 230v, a lot of the UK is still at a nominal 240v, so there shouldn't be any problems with 230v transformers running at 240v or there would be a lot of irate British customers!

Sounds like there might have been some other issues with the design of that amp as it's not something I've come across here. Possibly the factory buyer ordering some below-spec valve sockets because they were considerably cheaper without understanding the implications.

Very high plate voltages mean low current draw and apparently a lot more crossover distortion, so the plate voltage is normally kept lower, in the 400v region (unless you really want more power out of the valve at the expense of fidelity).


I've never actually tried JJ KT-77 valves before, so it'll be very interesting to hear what they sound like in practice, Evatco described them as sounding like a cross between an EL 34 and a 6L6, the original Soldano SLO 100 used 5881 power valves going by what I have read, EL 34 valves have that British crunch whereas the 6L6 has more of an American crunch going by what my ears tell me, in the Soldano SLO-100 schematics I'm working with, the screen grid resistors are 500 Ohms, in my build I changed them to 1k in value, I also made a simple mod to the power amp circuit to include an output power switch so the amp could be switched from the full 50W output to 25W output (Pentode/Triode mode switch).

Simon Barden
04-07-2023, 01:31 AM
It sounds like you may have more than 50W with the voltages present if you use the bigger transformer. Presumably the output transformer is OK for a bit more power?

DrNomis_44
04-07-2023, 04:44 AM
It sounds like you may have more than 50W with the voltages present if you use the bigger transformer. Presumably the output transformer is OK for a bit more power?

I was thinking of using the existing output transformer that was installed on the chassis, but seeing as I opted to buy a new power transformer, I decided to go ahead and buy a new choke and output transformer as well, the new output transformer is rated for 50W output, has a 3,400 Ohm CT Primary and is rated for a primary winding current of 318mA, one of the power valves Evatco suggests for the new output transformer is the EL-34, since the KT-77 is supposed to be a drop-in replacement for the EL-34 they should work fine with the new output transformer, I'm not sure what the primary winding impedance of the old output transformer is, but it is designed for two EL-34 valves, as far as I know it still works perfectly well.

Most likely I will get more output power with the JJ KT-77 valves since they're supposed to have more headroom than the EL-34, I was doing a search on google for information about the normal biasing current for JJ KT-77 valves, and it's about 30 to 35 mA per valve, an EL-34 can dissipate up to a maximum of 25W whereas a JJ KT-77 can dissipate up to 28W, I've heard some amp techs say to adjust the bias so that each power valve dissipates about 70% of the maximum power dissipation, some say to adjust the bias so that the power valves are dissipating 60% or 50%, I added two 1 Ohm/5W cathode resistors to each of the octal sockets from pins 1 and 8 to ground, doing this allows you to measure the current flow through each of the power valves with a multimeter, the 1 Ohm resistors convert the current to milivolts, so, I should adjust the -V Bias to read from .030 to .035V across each 1 Ohm resistor, saves doing some calculations.

DrNomis_44
10-07-2023, 11:56 AM
Update:

Got some more parts coming from Mouser Electronics in the post today, hopefully I'll be able to finally finish making the main HT power supply tagboard, as well as the power supply for the Vactrols that does all the channel-switching and muting.

Got some bills to pay this fortnight, but next fortnight I'll be able to start ordering the new transformers and 10H choke.


Update2:

These just turned up in the post, some 3W Metal Oxide Resistors, two electrolytic caps, and one 160V film cap.

44548

DrNomis_44
06-03-2024, 11:56 AM
Update:

Recently managed to make some more progress on building this amp after I ordered some stuff online from Evatco, I've got all the valve sockets wired up to the tagboards and pots, all I need to do to complete building all the circuitry is to order five new vactrols online from Evatco, then all that's left to do is order the new power and output transformer, choke, and a full set of JJ valves, plus some more 600V DC rated vintage-style cloth covered wire, and then I'll be able to finally complete the build process before doing all the testing/debugging/biasing, and then some play testing, will post some links to some demo recordings of the amplifier once I know it is all working correctly and sounding good.