Andy40's Mojotone Tweed Deluxe build diary

[Andy40]

Since it's my birthday and all. The birthday fairies granted me my wish!!!!!

I can put the costings up for anyone who is interested. But that is all for now.https://uploads.tapatalk-cdn.com/20181226/05bed4eaf9d6c338d01daf7a1898056b.jpg

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[Sonic Mountain]

That looks like fun :)

[DrNomis_44]

Oh cool, was wondering when you would have a go at building an amp, hey Happy Birthday mate!!!!


Hope it all goes well.

[Dedman]

ooooh tasty, my fav speaker cab has a jensen Falcon in it, great clean tones

[DrNomis_44]

My little Legacy amp has a Jensen C10Q speaker in it, I swapped out the stock speaker for the C10Q and it really made a big difference in tone, Jensen speakers are great ones, if I could find four good 100 Watt Jensens I'd stick them in the quad box for my Super Twin amp.

[Old Tooth Hopkins]

Awesome! Let me know where you ordered it.

I was told you need to be a qualified electrician to play with mains power. That’s why I never took the plunge


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[Bakersdozen]

Oh heck yeah dude, this is going to be an awesome follow! Happy New Merry to you!

[Andy40]

Costings
All right. So buffoon here did not take into account that the prices on Mojotone are American money! Don't make that simple mistake.
It's a straight Tweed 5e3 kit and they had a sale on at the time so I pushed the button on the kit and several other things (shhh).
The Tweed 5e3 kit complete (Export 240 Volt Aus) (with about 15% discount due to Thanksgiving sale) worked out to be about AUS$905.00.
Priority shipping with Fedex was about AUS$580.
Customs was about AUS$300 - but I had a bunch of other stuff there so I don't know what the amp kit would have been on its own.
Therefore, all up it was about AUS$1,785.:eek:

Edit: Customs and Taxes.

I got a bit more info on the customs and taxes. On this amp kit Customs charged me $32.99 in "duty" and $120.36 in "GST on importations".

Couple of points to note.
1. If you buy from Mojotone, from Australia, you will be charged GST (as they do not)
2. You need to keep the import documents for at least 5 years from date of entry - according to the Customs Act 1901, or its an offence on Australia.:mad:

[FrankenWashie]

Ooooooh that's a fair old whack of cash. Nearly as costly to ship and import it as it is to buy the Kit! DANG!

[Andy40]

Delivery
Once ordered they need to put the kit together and make the cab. Mojo says the lead time on Orders with woodworking is about 3 weeks.
I ordered mine on 21 November 2018 and the Order was fulfilled by 8 December 2018 and sent by Fedex.
The Order arrived here on 14 December 2018.

It was actually ready for delivery well before that but Fedex don't contact you until they know what the customs amount will be and it was very difficult to contact them back just to pay for customs. Often calling the right customs payment line at different times would just ring out.

Anyway, it was packaged quite well with sealed air expanding foam and brown paper packing. Everything from the amp kit was there.

They did forget to pack the Tweed Amplifier Logo that I had ordered separately. But I contacted Mojo and they send me one within a day. (still not arrived yet as slow shipping).

[Andy40]

Ooooooh that's a fair old whack of cash. Nearly as costly to ship and import it as it is to buy the Kit! DANG!

The joys of living in Oz my friend. but I did get the expensive shipping, normal shipping just for the amp kit would have been about $200

[FrankenWashie]

The joys of living in Oz my friend. but I did get the expensive shipping, normal shipping just for the amp kit would have been about $200

Yeah i had this conversation with a Canadian guy on the project electric guitar facebook page. Its as expensive for them to get stuff out of the US as it is for us and they are next door (so to speak).

Good old 'Straya tax.

[king casey]

R.E.S.P.E.C.T.
Getting that budget past admin. and then looking forward to the blood, sweat and tears putting it together.
oh...and Happy Birthday.

cheers, Mark.

[DrNomis_44]

Should turn out to be a really nice sounding amp, I'm about to pop in to my local Jaycar Electronics store for some bits and pieces to make a new footswitch for my Peavey Renown amp.


If you have any problems building the amp, just let me know and I'll be only too happy to help out.

[Sonic Mountain]

Therefore, all up it was about AUS$1,785.:eek:

Good Lord. That's a VOX AC30 with change leftover.

I guess you don't get the fun of building it, but that made my eyes water a bit.

[Andy40]

Good Lord. That's a VOX AC30 with change leftover.

I guess you don't get the fun of building it, but that made my eyes water a bit.

That's kind of why I posted the costings, for the benefit of others.

If you just want an amp that works, is not handwired, you don't want to try and electrocute yourself and don't really really like the tweed deluxe its not worth it.

[Andy40]

Ok detail shots. Cabinet is pine covered with Tweed olive stripe with oxblood grillcloth and fender style raised brown leather strap with chrome end caps.https://uploads.tapatalk-cdn.com/20181228/a41d26310ce07f7b11ce67f91887be70.jpghttps://uploads.tapatalk-cdn.com/20181228/14079d4a503764a3b270479edd49a6ce.jpghttps://uploads.tapatalk-cdn.com/20181228/cfd62dfe954c1edc0344d57e4558cd5c.jpg

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[DrNomis_44]

Looks awesome, does the tweed covering come pre-lacquered?, I'm assuming it does.

[Andy40]

Small parts kit, 2 6V6's, a 5Y3, a 12AX7, eyelet board and backing board, and transformers. 5e3 chassis - chrome plated cold roll steel. Finally, one Jensen C12Q Speaker! https://uploads.tapatalk-cdn.com/20181228/b49a4bcb1c0fdb1dc4fb6eff0db485dc.jpghttps://uploads.tapatalk-cdn.com/20181228/93e5c545913df93cac4c0c24914e8c4f.jpghttps://uploads.tapatalk-cdn.com/20181228/294d0c8116babd5d578d43396cf65820.jpghttps://uploads.tapatalk-cdn.com/20181228/029f765fcfa6a182eba0815d3fa67a9e.jpghttps://uploads.tapatalk-cdn.com/20181228/9964a2def369e505f1f5e85d0c695c47.jpg

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[Andy40]

Looks awesome, does the tweed covering come pre-lacquered?, I'm assuming it does.You can order it like that doc but I chose not to

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[DrNomis_44]

That reminds me, I need to order one of those 5W Pitbull Guitar amps, we'll see how we go this coming month.

[Simon Barden]

That reminds me, I need to order one of those 5W Pitbull Guitar amps, we'll see how we go this coming month.

You may have missed the boat on those as they are no longer sold on the PBG site. Adam may have a couple still lying around, so I'd email him ASAP just in case, but I don't think they sold quickly enough to make it worth getting another batch made-up.

[Simon Barden]

Interesting kit. A friend built a Ceriatone 5E3 and and it sounds very nice. I see they've gone for 'bright' and 'normal' channels rather than 'inst. vol ' and 'mic. vol' (for a high-impedance harmonica mic) as on the original amp's channel labelling.

One thing you might want to consider is internally linking the two channels together, rather than have to always use an external patch cord to do so. I've got a 5E5-A based amp and I'm planning to do that to that amp (the idea came to me in one of those semi-awake moments that I keep having at the moment when struggling to get to sleep and just went round and round in my head for about an hour). It looks like the jack sockets provided have a switching function on them (which means that you can use the channels separately for two inputs if you want).

[Andy40]

Thanks Simon. that's a pretty good idea. I hadn't thought of that.

[Andy40]

Wow so many learnings!
Before I touch anything, I need to know as much as I can about the circuit etc. I am going to get my father-in-law to put this together with me as he is a sparky, but I don't just want to let him do it. I want to learn as much as I can.
For those of you who don't know Uncle Doug on You Tube. He's a legend. Let me introduce you:
How Tube Amplifiers Work, Part 1: The Power Supply https://www.youtube.com/watch?v=x5SSKX74DKg
How Tube Amplifiers Work, Part 2: The Pre-Amp and Power Amp https://www.youtube.com/watch?v=901iaPVVzY0
(the 5F1 circuit is similar to the 5E3 circuit)

This is also a pretty nifty video on saftey: DIY: Amp Safety 101 https://www.youtube.com/watch?v=DkEc58-vWc4

Edit: I put this here to remind me to read it. https://robrobinette.com/How_The_5E3_Deluxe_Works.htm

[DrNomis_44]

Wow so many learnings!
Before I touch anything, I need to know as much as I can about the circuit etc. I am going to get my father-in-law to put this together with me as he is a sparky, but I don't just want to let him do it. I want to learn as much as I can.
For those of you who don't know Uncle Doug on You Tube. He's a legend. Let me introduce you:
How Tube Amplifiers Work, Part 1: The Power Supply https://www.youtube.com/watch?v=x5SSKX74DKg
How Tube Amplifiers Work, Part 2: The Pre-Amp and Power Amp https://www.youtube.com/watch?v=901iaPVVzY0
(the 5F1 circuit is similar to the 5E3 circuit)

This is also a pretty nifty video on saftey: DIY: Amp Safety 101 https://www.youtube.com/watch?v=DkEc58-vWc4


I've watched quite a few of his youtube videos, he certainly knows his stuff, I've even subscribed to his channel too, always great to watch and informative.

[Andy40]

Thanks Doc. No doubt I'll have some questions

[Richy17]

I’ll be keeping a close eye on this. Always something I’d like to try. As for the cost of the kit - I think it’s pretty reasonable considering what you will learn building it. I’ve always been fascinated with electronics and would love to learn more about it. Sure you could just walk into a shop and buy a nice valve amp for $1500 but what you’ll get from this is priceless. Good on you for having a crack Andy!

[DrNomis_44]

Yep I agree, you gain more from building an amp yourself than by buying one, plus you can customize it to your liking as well.

[Marcel]

There are so many times I've considered getting a kit like this... all the parts, a nice chassis and cabinet, nil stress on getting hard to find bits, and a set of instructions to put it together... and I always have rejected it because of the shipping and import duties.

Getting parts locally for my AC18W head cost me close to AU$900, and we all know how that shaped up... Lol.. My Blues Jr IV brand new and delivered only cost me AU$800...

Maybe one day when I win big on Lotto...

Happy birthday, and have fun...

[Andy40]

Still doing research before I start building.

Does anyone know the pros and cons of lacquering the tweed?

[Simon Barden]

The pros are that it keeps the tweed clean otherwise it can pick up a lot of dirty marks. Can't think of any cons. I recently varnished a tweed amp with a brushed-on single coat of water-based poly varnish and that was easy enough to do (and I could do it inside).

You can of course use a tinted lacquer to make it more yellow, like Fender do with their lacquered tweed cabs, but clear will provide protection if you want it to look more subdued.

[king casey]

You can of course use a tinted lacquer to make it more yellow

So you have that unused half a bottle of Tru-Oil sitting on the shelf.

cheers, Mark.

[Simon Barden]

Don't forget to remove the grille and all the other fittings first.

[Andy40]

Good points, thanks Simon.

[DrNomis_44]

Uncle Doug just recently uploaded a series of youtube videos about the Oscilloscope and how to use it to trace out the signal path of an amplifier, definitely a must watch series.

Hey Andy, how's the build process going?

[Andy40]

Thanks for the interest Doc. I'll definitely check out uncle Dougs vids. This year I'm getting absolutely flogged at work so I am hoping Ito get some time off at Easter to put this together. I have been checking out https://www.evatco.com.au/

for some pretty good quality amp parts. next time I think I'll just make my own cab and get the parts from there.

[Andy40]

Still on the information gathering stage as I'm a bit of a bookworm. I have to wait until Easter before my sparky helper is free anyway. I've ordered some books which I will give a review on one received and digested.
Found this nice video though, hopefully it will inspire someone else to give it a go as well.

http://www.youtube.com/watch?v=rBV4FYCPoIY&t=1970s

[Marcel]

Still on the information gathering stage as I'm a bit of a bookworm. I have to wait until Easter before my sparky helper is free anyway. I've ordered some books which I will give a review on one received and digested.
Found this nice video though, hopefully it will inspire someone else to give it a go as well.

http://www.youtube.com/watch?v=rBV4FYCPoIY&t=1970s

Yep, that's a great video Andy.... Some quite essential points covered however many critical points completely overlooked.... The main point I think they missed is the feeling you get when you play through an amp that you have built, but I also think the little jam they have more than makes up for it in spirit...

[Andy40]

My new book arrived today!!! Nerd excitement!!!https://uploads.tapatalk-cdn.com/20190328/242db92d755353b0a1e66f7695a4bd52.jpg

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[king casey]

My new book arrived today!!! Nerd excitement!!!https://uploads.tapatalk-cdn.com/20190328/242db92d755353b0a1e66f7695a4bd52.jpg

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Written by Frankie's side-kick.
Probably be a chapter on grave robbing.
cheers Mark.

[DrNomis_44]

I'll have to try building a Tweed Deluxe one day, I think Evatco sell the chassis and eyelet boards for Tweed Deluxes, they also stock the transformers as well.

[king casey]

I got curious and had a look on good o'l Amazon.
Only one review so far but quite a knowledgeable one...including a quote that gave me a chuckle.

'Guitar players wanting to learn how tubes and tube amplifiers work.’ I will state that most or all of the musicians I know wouldn’t get ten pages into the book before they started getting cross-eyed.

cheers, Mark.

[FrankenWashie]

Written by Frankie's side-kick.
Probably be a chapter on grave robbing.
cheers Mark.

Apparently the author was shunned at the last IFSOIAAH (International Friendly Society of Igor’s And Associated Henchpersons) conclave.
many have taken a dim view of his non traditional uses of electricity and his reluctance to promote reanimation of the dead for health and lifestyle benefits. He also suggested that more power is not always the answer, which really wound the society up. Igor (Igor, not Igor) was so shocked he lost his lisp and almost stood bolt upright.

[Andy40]

If you don't like physics and math this book is not for you.

[dave.king1]

My new book arrived today!!! Nerd excitement!!!https://uploads.tapatalk-cdn.com/20190328/242db92d755353b0a1e66f7695a4bd52.jpg

Damn I remember our eyes glazing over doing electronic theory at college, particularly in the first year when it was all new to us.

I mean you plugged your guitar into the amp, hit the power switch and magic happened in that big box, a pimply face kid didn't need to know how things worked.

What really made me get stuck into learning and understanding was drawing a circuit for homework on the train into college one day and this rather attractive young miss leaned over my shoulder and told me I had drawn a tetrode instead of a pentode and that type of valve didn't belong in that part of the circuit.

I was 15 at the time and I guess she was about the same age

[DrNomis_44]

Jaycar Electronics were selling a pretty good book called "Build Your Own Audio Valve Amplifiers" by Rainer zur Linde, it mainly deals with HiFi valve amplifiers, but it does have a section on guitar amplifiers too, it also includes lots of circuits, circuit board artwork and construction projects as well.

30396

[Marcel]

What really made me get stuck into learning and understanding was drawing a circuit for homework on the train into college one day and this rather attractive young miss leaned over my shoulder and told me I had drawn a tetrode instead of a pentode and that type of valve didn't belong in that part of the circuit.

I was 15 at the time and I guess she was about the same age

Did you marry that young miss Dave ??

[dave.king1]

Did you marry that young miss Dave ??

Nah, she was far to intelligent to be attracted to the likes of me :D

[WeirdBits]

There’s something seriously wrong with that book... too much damn reverb!

30398

[Rabbitz]

There’s something seriously wrong with that book... too much damn reverb!



Dick Dale and Martin Cilia may disagree.


https://youtu.be/qmMeqid_fmU

[Andy40]

There’s something seriously wrong with that book... too much damn reverb!

30398

Nice one Weirdy.

[Fretworn]

RIP Dick Dale, but all that spring reverb was bound to get you in the end..........

If only playe reverbs were portable........

[DrNomis_44]

Dick Dale did a pretty good version of Pipeline with Stevie Ray Vaughan, a mate of mine wants to do a cover version of it with me as part of a live gig performance.

[Fretworn]

I used to play Pipeline with the band I was in decades ago in my gigging days.

[Andy40]

So much makes more sense now....

Tweed Era Model Number System
The first number indicates the decade: 5 = 1950's, 6 = 1960's.

The second letter indicates the cabinet type: A & B = TV Front, C & D = Wide Panel, E & F = Narrow Panel, G = Brown, Blonde or Black Tolex.

The third number indicates the model with 3 = Deluxe.

So "5E3" = 1950's Narrow Panel Deluxe.

[Andy40]

Finally got around to lacquering that tweed!https://uploads.tapatalk-cdn.com/20190719/20ef0a025ef5362a83024b0b92c81e0d.jpg

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[DrNomis_44]

@ Andy40 Looks nice, bet it sounds really good too.

[Andy40]

Progress update.....glaciers move faster than me....https://uploads.tapatalk-cdn.com/20191227/8819d52c5dbfadd8b0f668455051f3cc.jpg

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[DrNomis_44]

Hey Andy40, you've done some nice looking work on that eyelet board, looks nice and neat to me, that's going to be a big help when it comes to testing and troubleshooting the amp, and the way you explained the Fender amp model-numbering system makes a lot of sense to me too.

[Marcel]

Progress update.....glaciers move faster than me....https://uploads.tapatalk-cdn.com/20191227/8819d52c5dbfadd8b0f668455051f3cc.jpg

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Yup, very nice work there Andy.
Remember to check everything, and when done check everything again....

[DrNomis_44]

@ Andy40 If you ever end up needing to order valves or new parts for your amp, there's a great company located in Australia called Evatco that you can order stuff online from rather than having to order from the US, here's a link to the Evatco website:

https://www.evatco.com.au/

[Andy40]

thanks doc. 'll post a pic of the completed chassis tomorrow. I'll be firing her up tomorrow arvo so if I blow anything, I'll be ordering aprts from these guys.

[DrNomis_44]

Seeing as Evatco do have 5E3 amp chassis in stock, I'm going to look at buying all the parts needed to build a 5E3 amp next year, would be cool to have one so I can take it to the Nirvana club just up the road for a jam.

[Simon Barden]

How do they suggest the initial firing up? I'd do it in stages. Start without any valves fitted, just in case there are some obvious shorts that take out the main fuse, then add the rectifier valve and test, then the pre-amp valves and test, then add the the power amp valves. (Don't forget to have the right impedance load connected).

Hopefully nothing goes wrong and you get a wonderful Deluxe sound.

[DrNomis_44]

First thing I would do after completing an amp build like this is to go have a good break to refresh, and then come back to it with a fresh mind, then I would check all the solder connections to make sure I hadn't made any mistakes, and then I would start doing all the test procedures prior to installing any of the valves.

[Andy40]

Thanks doc and Simon. It took me a lot longer than expected. Doc was right taking breaks and coming back to check. I did find the odd mistake that way.https://uploads.tapatalk-cdn.com/20191229/0fe3588321c49b3ddac44e92fe531d81.jpghttps://uploads.tapatalk-cdn.com/20191229/50269748061a24b149730ff5851431b4.jpg

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[Andy40]

Simon. They do recommend that you check the voltages in stages. Unfortunately and weirdly without the full load of all tubes and speaker plugged in I was getting some really high voltage readings.

Anyway maiden schwang worked great. It sounded a lot better than I thought it would.https://uploads.tapatalk-cdn.com/20191229/3161981a03b409756b26ded7796b5402.jpg

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[DrNomis_44]

With just the rectifier valve plugged in (I'm assuming it's a 5Y3 valve), the voltages will be higher than normal because the power supply isn't being loaded-down by the other valves, once the rest of the valves are plugged in you'll find that the voltages will drop-down to about where they should be, the two 6V6 power valves will be drawing the most current from the power supply out of all the valves together, on the other hand if the voltages were higher than what they should be when all the valves are plugged-in that would indicate that something is wrong, but since the amp seems to be sounding good, then it looks like it's all working as it's supposed to, but a good idea is to check the voltages with all the valves plugged in and compare them to what the assembly manual says they should be, it's okay if the voltages are a little-bit higher with all the valves plugged-in, but not significantly higher.

[Andy40]

Yep you are right Doc.
Look the instructions require you to check certain voltages before you plug valves in.
Then check voltages after the rectifier (5Y3 - yes you are right) but as you pointed out it was heaps higher without any of the other valves plugged in.
Once the others and the speaker was plugged in the voltages were pretty good.

I muffed the Normal jacks somehow, I think I have a old solder joint there somewhere. I'm going to discharge the CAPS and fix it later or tomorrow when the wife's around.

A few questions for you doc:

I think I read somewhere that you have build some kind of bleeder that will bleed the caps to ground when you turn the amp off? or did I make that up?

I think i'm going to place an order for replacement valves from Evatco and another slow blow fuse, what brand of valves would you buy?
Its currently got JJ's in it

[DrNomis_44]

Yep you are right Doc.
Look the instructions require you to check certain voltages before you plug valves in.
Then check voltages after the rectifier (5Y3 - yes you are right) but as you pointed out it was heaps higher without any of the other valves plugged in.
Once the others and the speaker was plugged in the voltages were pretty good.

I muffed the Normal jacks somehow, I think I have a old solder joint there somewhere. I'm going to discharge the CAPS and fix it later or tomorrow when the wife's around.

A few questions for you doc:

I think I read somewhere that you have build some kind of bleeder that will bleed the caps to ground when you turn the amp off? or did I make that up?

I think i'm going to place an order for replacement valves from Evatco and another slow blow fuse, what brand of valves would you buy?
Its currently got JJ's in it


Yes, you can make a special bleeder-probe to discharge the supply filter caps after you turn the amp off and completely disconnect it from the mains by un-plugging it, you can make a bleeder by attaching a resistor to a piece of wooden dowel, and then solder a piece of wire with an alligator-clip to one end of the resistor, the other end can either be attached to a small nail driven into the end of the wooden dowel or used as is, when you use the bleeder-probe to discharge the caps, the alligator-clip is clipped onto a convenient place on the chassis of the amp, which is normally securely tied to ground, the other end of the bleeder-resistor is touched to the positive terminals of the caps, I need to make a bleeder-probe since I'm going to be doing some amp-building work next year, I just found a piece of 8mm Oak doweling that I could use to make a bleeder-probe, dry-wood is a good electrical insulator, but you can also use a piece of PVC piping cut to a suitable length, a bleeder-probe is a handy piece of equipment to have when it comes to servicing a valve amp.

What I like to do while I'm discharging supply filter caps is to use a digital multimeter to monitor the voltage as I discharge the caps so I know that there aren't any dangerous voltages lurking in the amp circuits I'm working on.

Maybe I could start a thread about making a bleeder-probe, as I think it would prove to be quite useful.

When you choose a resistor for bleeding supply filter caps, you should pick a resistance value that's high enough so that you don't get a big spark when you touch it to the positive terminal of the cap, but low enough so that it bleeds-off the voltage quickly enough, you could probably use any value from about 10k to maybe 220k, and a power rating of maybe 1 Watt to 5 Watts, Marcel might be able to suggest a suitable resistance and power-rating for a bleeder resistor.


I've heard that JJ's are supposed to be a good brand of valves, although I've never tried them....yet, I've got a couple of Genelec E83CC Gold Lion gold-pin preamp valves installed in my Marshall MA100C amp and I think they are pretty good, although they did cost me about Au$50.00 each, I guess it really depends on how much you are willing to spend on valves, I personally wouldn't buy cheap valves since you never know when they'll go bad, and usually with no warning, Electroharmonix are supposed to be pretty decent, as are Sovteks, I read somewhere that Mullards are supposed to be some of the best valves you can buy but they tend to be pretty expensive, Shugangs are supposed to be good too, new old-stock RCA's are supposed to be pretty good too, generally, pretty much all the brands of valves that Evatco stock are good.

I've got a couple of Trigon 6SN7GT octal-base twin-triode valves that seem to be pretty good, and I just remembered that i happen to have one American-made General Electric 6V6GT valve in my stash of valves, I might use it to make a Fender Champ one day.


Anyway, I personally would try and buy the best quality brand of valves I could afford for any of my valve amps, depending on my budget, the better the quality of the tube/valve, the more expensive it's going to be, some audiophile-grade valves, like a new old-stock vintage 300B audio power-triode can cost quite a bit of money.


There's nothing wrong with doing what's called "Tube/Valve-rolling" which is basically trying tubes or valves of different brands in your amp till you find a brand that works for you.


Some of the valves in my stash of valves were scrounged from some defunct electronic equipment, I remember one time when I was studying electronics at uni in the mid 90's, they were getting rid of some unwanted stuff, and I managed to score myself a big box of miscellaneous valves for nothing but my time, including quite a few AWA brand 6CA7 valves, which are equivalent to EL34s, they were still in their original cardboard boxes, unused, wish I still had them now, there were also quite a few 12AU7As and 12AT7s, as well as 12AX7s, really kicking myself now that I didn't bring them with me when I moved to Darwin in 2000.


Going back to the bleeder-resistor, some valve amps, like Marshalls and Fenders, have a bleeder resistor permanently soldered in, in parallel with the power supply filter caps, this does two things I can think of, firstly, the resistors equalize the voltage across two electrolytic caps if the caps are placed in series to double the working-voltage of the cap, have a look at the power supply circuit of a Fender Twin and see if you can spot the two caps in series with the bleeder resistors connected in parallel, the resistors will be something like 220k in value, the two series-connected supply filter caps will usually be placed after the standby switch, the second thing that the bleeder resistors do is to bleed-off the voltage when the amp is powered-down as part of a safety feature, but it's always a good idea to check that there aren't any dangerous voltages remaining in the amp after it has been powered-down and completely disconnected from the mains supply, since bleeder resistors have been known to fail.

[dave.king1]

If you are making your own probe please shrink wrap it leaving only the tip to prevent unintentional shorts.

When I was in college a lifetime ago it was just a matter of shorting the cap with a screwdriver, brutal but effective and not recommended today.

Back then transistors were the future and ICs didn't exist ( who remembers hole theory for current flow )

[DrNomis_44]

If you are making your own probe please shrink wrap it leaving only the tip to prevent unintentional shorts.

When I was in college a lifetime ago it was just a matter of shorting the cap with a screwdriver, brutal but effective and not recommended today.

Back then transistors were the future and ICs didn't exist ( who remembers hole theory for current flow )


Yep, good idea and I certainly will do that, cheers!!!

[Simon Barden]

My amp tech (a chap I've started using this year for my Sound City amp head rebuild) recommends Sovtek valves. JJ are OK, but not as good as they were, and I know as a result that Blackstar stopped fitting them as standard a couple of years ago. But if they work and the amp's not noisy, and there are no microphonic or rattling valves, then there's really no point in replacing them for the sake of it.

[DrNomis_44]

I agree with what Simon said, if the JJs are working fine and aren't microphonic then there's no real need to swap them out, you can test each valve to see if they are microphonic by gently tapping the glass envelope with a pencil and listening for any ringing coming through the speaker, if a valve is microphonic it will tend to ring if it is gently tapped, some valves won't ring much and you might just hear a slight "tink" when the valve is gently tapped, some will ring a lot and be very sensitive to the point where you'll hear something coming through the speaker that sounds like feedback, generally the valve that has the first two triode gain-stages in it will be more susceptible to being microphonic, sometimes a power valve will become microphonic.

When a valve becomes microphonic it's usually caused by the internal electrodes becoming a bit loose in their mountings, this can happen when the valve is made at the factory, or it can happen over time from vibrations from the speaker, or when the amp is transported in a car.

One scenario where I would definitely swap out the valves is if one of the power valves starts to develop a red or orange glow on the plate, this is known as red-plating, I'd swap the valves if I'm absolutely certain that the bias circuit is working correctly and set to the correct bias voltage, there are no leaky coupling caps, all the socket pins are making good contact, and there are no other causes, like a shorted output transformer primary-winding, I would suspect a faulty power valve.


If you see a blue flourescence, or glow, inside the glass envelope of the power valves when the amp is fully powered-up, that's normal, if you see a lilac or pinkish glow inside the glass envelope of the rectifier valve, and the silver getter is turning a whitish colour, then it means that air has gotten inside it and the rectifier valve definitely needs replacing.


A preamp valve that has excessive hum should definitely be replaced.

[Simon Barden]

There are in fact only three factories making guitar valves. Everything else is badging. Interesting read:

https://valvetubeguitaramps.com/valve-supplier/

[Andy40]

Wow, what a fantastic response guys. Thanks so much.

Alright, I've got a bleeder probe. - stewmac has a "snuffer stick" that uses two 56k resistors in series.

The permanent bleeder as a mod was the thing I was thinking.

Anyway I'll have a go a trouble shooting this morning. If I have issues with the voltages, I'll post them.

[DrNomis_44]

Wow, what a fantastic response guys. Thanks so much.

Alright, I've got a bleeder probe. - stewmac has a "snuffer stick" that uses two 56k resistors in series.

The permanent bleeder as a mod was the thing I was thinking.

Anyway I'll have a go a trouble shooting this morning. If I have issues with the voltages, I'll post them.


No worries at all, I'm only too happy to help out whenever I can, hope all the troubleshooting goes well and you end up with great sounding amp that works as it should, two 56k resistors in series (that gives a total value of about 112k) should work fine for discharging the power supply filter caps.

[Marcel]

As Doc said, you can fit a permanent bleed resistor on the HT line, and on my amp builds I always do.

My go to is typically a 470k 1W from HT to ground at any convenient location. Often that will be near the main filter caps. If the HT voltage is around 300VDC then a 470k will draw about 0.6mA and develop 0.2W of heat .. On a 600VDC HT rail I will put a 1M 1W resistor which will draw again about 0.6mA but will develop about 0.4W of heat... (E=I*R, P=I2*R)

Remember that the entire HT rail is connected by a DC path so putting a 470k resistor on the common HT distribution point of the preamp stage (where voltages are often around 300VDC) is just as effective as a 1M on the main filter cap (where on larger amps can be in the 600VDC range), only difference is the ultimate safe discharge time with the resistor on the preamp is it will take near twice or four times as long....

One must always remember too that the permanently fitted bleed resistor is drawing current, which may change some HT rails nominal voltage. On a Marshall design the step down resistors for each stage from power amp stage to preamp are cascaded (or in series if you prefer), so that extra 0.6mA of essentially wasted HT power will draw down the HT power available to the preamp should you put the bleed resistor there. An extra 0.6mA going through those two typically 10k HT dropping resistors that feed V1 and V2 may not sound like much but it can change the whole character of the Amp for the better or the worse, so be aware

Doc's clip on 56k is great as it will get rid of most of the charge on those filter caps pretty quick, and render the amp fairly safe in a short time to allow a safe servicing environment. But resist the temptation of fitting a 56k 5W resistor permanently..... 56k at 450VDC is 8mA which is a significant percentage of what most guitar amp HT power supplies can create in the first place, and with 3.6W of pure heat being generated from this one resistor inside the amp case is simply a waste of energy. In the case of a Blues Junior amp from Fender the HT supply can at best only give around 120mA so 8mA is theft of near 10% of the amplifiers potential noise with nil benefit to the player...

[DrNomis_44]

As Doc said, you can fit a permanent bleed resistor on the HT line, and on my amp builds I always do.

My go to is typically a 470k 1W from HT to ground at any convenient location. Often that will be near the main filter caps. If the HT voltage is around 300VDC then a 470k will draw about 0.6mA and develop 0.2W of heat .. On a 600VDC HT rail I will put a 1M 1W resistor which will draw again about 0.6mA but will develop about 0.4W of heat... (E=I*R, P=I2*R)

Remember that the entire HT rail is connected by a DC path so putting a 470k resistor on the common HT distribution point of the preamp stage (where voltages are often around 300VDC) is just as effective as a 1M on the main filter cap (where on larger amps can be in the 600VDC range), only difference is the ultimate safe discharge time with the resistor on the preamp is it will take near twice or four times as long....

One must always remember too that the permanently fitted bleed resistor is drawing current, which may change some HT rails nominal voltage. On a Marshall design the step down resistors for each stage from power amp stage to preamp are cascaded (or in series if you prefer), so that extra 0.6mA of essentially wasted HT power will draw down the HT power available to the preamp should you put the bleed resistor there. An extra 0.6mA going through those two typically 10k HT dropping resistors that feed V1 and V2 may not sound like much but it can change the whole character of the Amp for the better or the worse, so be aware

Doc's clip on 56k is great as it will get rid of most of the charge on those filter caps pretty quick, and render the amp fairly safe in a short time to allow a safe servicing environment. But resist the temptation of fitting a 56k 5W resistor permanently..... 56k at 450VDC is 8mA which is a significant percentage of what most guitar amp HT power supplies can create in the first place, and with 3.6W of pure heat being generated from this one resistor inside the amp case is simply a waste of energy. In the case of a Blues Junior amp from Fender the HT supply can at best only give around 120mA so 8mA is theft of near 10% of the amplifiers potential noise with nil benefit to the player...



Yep, a typical 12AX7 triode gain-stage as found in a Fender or Marshall amp tends to draw about .005 mA of current, that's 5 micro-amps (or maybe as much as 1mA depending on the values of the cathode and anode resistors since they determine the maximum saturation current) from the power supply when it is fully turned-on or saturated (going by what I've seen looking at a characteristic graph of a 12AX7 in a valve manual) assuming that the plate voltage is from about 250VC to 300V DC (the 12AX7 is designed to work with plate voltages of a maximum of 300V DC) , 8mA is significantly more current than .005mA so I can see why it would change the character of the amp, due to loading effects.


Sorry if I'm going off on a bit of a technical-tangent here.

[Andy40]

Hi Guys,

Thanks for that guidance.

Okay, I'll look into the best point to put a bleed resistor in but for now I've been successful on draining the filter caps, and pulled the chassis out and buzzed out the circuit.

I found the culprit being the bridge between pins 8 and 3 on the 12AY7, there was a loose connection there.

It also gave me a chance to check and recheck all of the solder joints and reflow a couple that I did not like.

All voltages are reading within their tolerances except for one being the PI grid leak from the 1M resistor going to pin 7 of the 12AX7.

Apparently its supposed to be 19V and its reading 2.71V which is quite low.

I can't for the life of me figure out why, except that the carbon comp resistor may be not within specs. I was actually quite surprised at how inaccurate the carbon comp resistors were wiht tolerances. I think if I build one again it would be with a turret board and metal film resistors.

Anyway, all input channels are working perfectly and the amp sounds and feels amazing.

[DrNomis_44]

Hi Guys,

Thanks for that guidance.

Okay, I'll look into the best point to put a bleed resistor in but for now I've been successful on draining the filter caps, and pulled the chassis out and buzzed out the circuit.

I found the culprit being the bridge between pins 8 and 3 on the 12AY7, there was a loose connection there.

It also gave me a chance to check and recheck all of the solder joints and reflow a couple that I did not like.

All voltages are reading within their tolerances except for one being the PI grid leak from the 1M resistor going to pin 7 of the 12AX7.

Apparently its supposed to be 19V and its reading 2.71V which is quite low.

I can't for the life of me figure out why, except that the carbon comp resistor may be not within specs. I was actually quite surprised at how inaccurate the carbon comp resistors were wiht tolerances. I think if I build one again it would be with a turret board and metal film resistors.

Anyway, all input channels are working perfectly and the amp sounds and feels amazing.


Most carbon composition resistors are usually marked with either a gold tolerance band (+/- 5%) or a silver band (+/- 10%), occasionally you might get a carbon composition resistor marked with either of those bands but when you measure them with a multimeter they measure significantly out of tolerance, in that case I'd personally replace it with one that measures within tolerance, it sounds like that 1M resistor might be partially short-circuited if the voltage reading is that low, there could also be something causing a leakage-path in parallel with that resistor, I seem to remember reading somewhere on the internet that some old Fender amps had eyelet boards in them where some parts of the vulcanized fibre-board got a bit damp and a leakage-path developed between some of the eyelets, that's more likely to occur in old vintage Fender amps rather than modern reproductions, sometimes solder flux residue can become slightly conductive and create a leakage path too, sometimes a valve can develop a leakage-path between two of it's pins, this is caused by a process called Ion Migration, and tends to happen between two pins at different voltages, try temporarily replacing that 1M carbon comp resistor with a 1M/5% 1W carbon film resistor and see if that restores the voltage to it's correct value, hope that helps.

You could also try substituting another known good valve for the phase inverter valve, and see if that fixes it too.


It is fairly common for carbon composition resistors to be a bit inaccurate with regards to tolerances, a lot of that is caused by the way a carbon comp resistor is manufactured, carbon film resistors do tend to be a bit more accurate and metal film resistors do tend to be pretty accurate (within +/- 1% or less of the marked value), I also remember reading somewhere on the internet an article about a type of harmonic distortion generated by carbon comp resistors due to the voltage-dependent nature of the resistive carbon material used to make them, supposedly the distortion caused by carbon comp resistors is part of why vintage valve guitar amps sound the way they do, because the distortion adds pleasing harmonics, though whether that is actually true or not I don't really know for sure.

https://www.diystompboxes.com/pedals/rgccmp.html


When a carbon comp resistor overheats they tend to drift up in value and will measure out of tolerance with respect to the marked value, incidentally, the reason why a resistor is made to a certain tolerance is because it's very difficult to make them exactly spot-on in value, most electronic circuits are normally designed so that the component values aren't too critical for normal circuit operation, if a circuit calls for a particular value of component and the person building it doesn't have it in stock, they can substitute the next higher value and the circuit should operate as it is supposed to, unless the circuit is for some particular application where high-precision is important, so say for example you're building a circuit and one of the components is a 10k/5% carbon composition resistor, and you don't have any in stock, but, you do happen to have some 12k/5% 1W carbon film resistors and you pick one, measure it, and it actually measures about 11.75k, if you use it as a substitute for a 10k resistor in the circuit, the circuit should still operate as it is supposed to .

[Simon Barden]

Are you sure all those resistors are the right values? I'm having trouble telling from the photo what's a blue and what's a green band. Going by the 56k resistor two along from the 1M in your board, It looks like the 1M has a blue not green 3rd band, so is a 10M resistor. But it may just be the light in the photo.

[Andy40]

Are you sure all those resistors are the right values? I'm having trouble telling from the photo what's a blue and what's a green band. Going by the 56k resistor two along from the 1M in your board, It looks like the 1M has a blue not green 3rd band, so is a 10M resistor. But it may just be the light in the photo.

Thanks Simon, that would have explained it too, but I double checked and tested it, its a 1M within tolerance.

[DrNomis_44]

Thought I would post a link to this webpage article that I just found since I think it's quite relevant and might prove to be useful, anyway:

https://robrobinette.com/How_The_5E3_Deluxe_Works.htm



After studying the 5E3 schematic a bit, I'm wondering if the 1.5k resistor going to pin 8 of the Phase Inverter valve might be the cause of the wrong voltage on that 1M resistor since it forms part of a voltage divider with a 56k resistor that's connected to ground, the 1M resistor is connected to the junction of those two resistors and connects to pin 7 of the Phase Inverter, might be worth checking the 1.5k resistor and 56k resistor to see if they are correct.


What voltage reading are you getting on pin 8 of the Phase Inverter valve?, I'm suspecting that the 1.5k resistor might have gone a bit low in value, or it could be partially short-circuited which might be the reason why you're getting such a low voltage on that 1M resistor, the colour-coding on that 1.5k resistor should be brown, green, red, and gold if it's a 5% tolerance resistor.


It could also be that the 56k resistor might have gone low too and is pulling pin 7 of the Phase Inverter down, the other possibility is that you might have a dry solder-joint in the eyelet that forms the junction of the 1M, 56k, and 1.5k resistors.

[Andy40]

ThanksDoc, I'll pull it apart and check it this weekend and let you know.

[DrNomis_44]

ThanksDoc, I'll pull it apart and check it this weekend and let you know.


How did it go?