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DrNomis_44
15-03-2017, 07:17 PM
Hi Everyone,

One of the students doing a different music course than the one I'm doing, has offered to sell me a Fender Super Twin amp chassis for $300.00, it looks in reasonable condition, except for a missing control knob, and apparently it does work.

I'm going to organize paying him the money for it over the next couple of fortnights, it looks like it could be a good amp restoration project, I'll post a pic of it once I get it home so you can check it out, it is an all valve amp that is apparently capable of putting out 180 watts of audio power

Stay tuned for more updates.

wazkelly
15-03-2017, 07:58 PM
Bargain price if not too much wrong with it. You mention amp chassis which implies no speakers and possibly no longer contained with original amp/combo setup?

DrNomis_44
15-03-2017, 08:06 PM
Bargain price if not too much wrong with it. You mention amp chassis which implies no speakers and possibly no longer contained with original amp/combo setup?


Yep, the chassis itself is housed in an old Fender Bassman head cabinet that has the front missing, the front panel of the chassis is still good though, what I can do tomorrow is take my Samsung Galaxy Y phone into uni and use it to take a pic of the amp chassis and post it in this thread so you can see exactly what it looks like, it's a Fender Blackface Super Twin with the EQ and Distortion control next to the Master Volume control.

And I'm guessing that it's probably an early 70's model.


Apparently, this is what they looked like brand new:

18109

DrNomis_44
16-03-2017, 04:19 PM
Update,

I've been having some trouble getting my laptop to connect to the Uni's Student WiFi network in order to get online, and seeing as the guy who's selling the amp chassis to me said I could take it home with me today, I'm going to see if I can get a couple of pics of the amp chassis "as is" sorted for you guys to check out shortly, will post them in this thread, stay tuned.


I've got the amp chassis at home now, it's in my loungeroom.

Simon Barden
16-03-2017, 06:09 PM
It's going to be very loud. They were known for regularly burning out the 2 x 100W JBL speakers that were fitted as standard in the combo when the amp was pushed. Probably not surprising as the wattage rating is normally given with the signal to the speakers at 3%THD, so still very clean, whilst when pushed into heavy overdrive you might get another 50%-80% more power from the amp. But those JBL speakers were also a few dBs more efficient than the normal Jensen or Eminence speakers Fender normally used at the time, so it was an even bigger volume jump over their standard models (though in the 70s you could also get the Twins fitted with the JBLs).

It was obviously designed to be a very loud clean amp, but it did make a very good even louder distorted amp (replacement speakers at the ready) when used by people like Ted Nugent, who used six of them on stage!

DrNomis_44
16-03-2017, 07:08 PM
I just took a couple of pics of the amp chassis with my Galaxy Y phone, just waiting for Windows Update to finish updating Windows 10 on my laptop, after that I'll get the pics sorted out so that I can post them in this thread.


While waiting for Windows to finish updating, I thought I would see what valves were installed in the chassis, here's what I found:


Three 12AX7 valves, one 7025 (basically a lower-noise version of the 12AX7), one 12AU7A, and six 6L6 power valves!! :eek:


Here we go, as promised, the pics of the amp chassis "as is":


18137

18138


Should make a pretty good amp restoration project.


So, it's looking like I'll have to build myself a 400 Watt Dummy Load for testing the amp's performance once I get round to doing whatever restoration work on it that it needs to get it up and running again, I wonder where I could source a new combo cabinet for it from?, or, should I just keep it as an amp head and invest in a new 4 X 12 Speaker box?

It'll probably be good for annoying my noisy neighbors....heehee.....180 Watts of audio power.

dave.king1
17-03-2017, 05:10 AM
It ain't 180w of audio power it's 180w RMS which is significantly more, there was a bass equivalent that one of my mates owned back in the day.

Heavy as hell and even louder, excellent if you are planning a Ted Nugent tribute show

stan
17-03-2017, 05:43 AM
Awesome project indeed, it will be a beast

Simon Barden
17-03-2017, 08:25 AM
I'd keep it as a head and get a 4x12 and make sure it's got at least 75W speakers (300W total) in it. It must be heavy enough as it is. Stick it in a solid wooden combo cabinet, add two 100W+ speakers and it's going to be a two person job to move it safely.

DrNomis_44
17-03-2017, 01:30 PM
I'd keep it as a head and get a 4x12 and make sure it's got at least 75W speakers (300W total) in it. It must be heavy enough as it is. Stick it in a solid wooden combo cabinet, add two 100W+ speakers and it's going to be a two person job to move it safely.


If I got a 4 X 12 and put four 75 Watt Eminences in it like the ones in my Marshall amp, the Fender Super Twin should sound good through them, shouldn't it?, I think some Fender amps did use Eminences, some used Jensens for sure, maybe some 75, or 80 Watt Jensens might work too.

And yep, it is a heavy amp, I was just able to manage carrying it up one flight of stairs by it's carrying handle when I got it home yesterday, I estimate that it must weigh at least 50kgs or so, that's going by my weight which is about 60kgs and I can just about manage one chin-up on a horizontal bar.

Hobastard
17-03-2017, 02:03 PM
Cool Score... Quad box is definitely the way to go...

wazkelly
17-03-2017, 05:12 PM
You won't need a gym membership if you plan on lugging that thing around haha.

Simon Barden
17-03-2017, 06:23 PM
I wouldn't worry too much about the maker, rather the specifications and frequency responses of any speaker you fit in them. Fender started with a mix of speakers, then settled on Jensen, but then used JBL for some of the higher powered amps and then swapped to Eminence or re-badged Eminences for a long time. Now they offer Jensen, Eminence and Celestion depending on the amp or special editions of their standard ones.

Some of those Eminence speakers are very heavy. I've recently bought a used turret post hardwired Fender 5E5-A (Tweed Pro) conversion of a Blues Deluxe (using only the cab, chassis and input and output transformers from the Fender). Whoever had it before me had fitted an Eminence Redcoat 'The Governor' speaker in it. Weighed 13lbs/5.9kg on my digital scales (it's supposed to weigh less). I replaced it with a Celestion Neo Creamback that weighed 4lbs/1.8kg. That's a lot less weight to lug around!

But any 4x12 cab that can handle 300W+ needs to be sturdy or it will add all sorts of resonances of its own. So the wood itself needs to be pretty solid and heavy, so going for light neodymium magnet speakers would be a good move (though expensive).

But you may find that the amp is just too loud for your needs. Most valve amps need to be turned up to a reasonable percentage of their output volume before they come to life. If you were a pedal steel or lap steel player then it might be ideal as you can get loads of clean volume from it, but unless you were touring stadiums, then it's probably too loud for rock use.

I'd look at renovating the head first and getting the woodwork looking nice, then trying it with a borrowed 4x12 cab (or two) to see whether you think it's your style of amp. You may be better off selling it on for a profit and getting something that's a bit more your style.

wazkelly
17-03-2017, 06:37 PM
Good comments Simon.

In one of several band line ups about 35 years ago a lead guitarist had a Fender Twin Reverb, 100w from memory, and it sounded gutless until our sound guy pulled 2 of the valves out, not sure which ones, but that trick really transformed the amp and gave it the warmer bordering on crunchy valve sound it lacked before.

Hey Doc, I reckon you probably know more than that bloke and could figure out a way to load up the output valves without lifting the decibels. 180w is a massive overkill and could end up way too loud before it sounds any good. That was the problem I had with my JMP 100w Super Bass head as there was no master volume. Sounded great clean but needed a Boss OD-1 to bring out the true Marshall distorted tone.

DrNomis_44
17-03-2017, 08:05 PM
Good comments Simon.

In one of several band line ups about 35 years ago a lead guitarist had a Fender Twin Reverb, 100w from memory, and it sounded gutless until our sound guy pulled 2 of the valves out, not sure which ones, but that trick really transformed the amp and gave it the warmer bordering on crunchy valve sound it lacked before.

Hey Doc, I reckon you probably know more than that bloke and could figure out a way to load up the output valves without lifting the decibels. 180w is a massive overkill and could end up way too loud before it sounds any good. That was the problem I had with my JMP 100w Super Bass head as there was no master volume. Sounded great clean but needed a Boss OD-1 to bring out the true Marshall distorted tone.


I guess I could mod it so that it only uses two 6L6 power Valves, and then just swap out the output transformer for one suitable for two 6L6 valves, that would bring the output power down to about 60 Watts max, but then again the HT from the power transformer might be a bit high, I know someone who I could consult for advice, he used to do a lot of tech work for Darwin musicians and fixed my Marshall amp so that it no longer blew fuses at random intervals.


If it turns out not to be very cost effective to restore the amp, I might use some of the parts to get my Soldano Amp head going.

Simon Barden
18-03-2017, 01:42 AM
There will be some people interested in a working Super Twin amp in a head version. All the existing head needs is a new front panel and re-Tolexing to look good (though maybe some side handles would be a good idea as well!). It does look rather rusty, so it really needs to be looked over by an amp tech to make sure its safe to use. The existing knobs look rather dirty and faded, so worth seeing whether they clean up easily. If not, the knobs are easy to get on eBay, it's just knowing if you'll need to order one or twelve!

Simon Barden
18-03-2017, 02:15 AM
While waiting for Windows to finish updating, I thought I would see what valves were installed in the chassis, here's what I found:


Three 12AX7 valves, one 7025 (basically a lower-noise version of the 12AX7), one 12AU7A, and six 6L6 power valves!! :eek:

OK, bad news. Looking on the web for a schematic of the amp, one thing is certain - it shouldn't have three 12AX7s in it! http://acruhl.freeshell.org/mga/schematics/amps/supertwin.jpg

The valves should be:

V1 = 7052
V2 = 6CX8
V3 = 6C10
V4 = 12AX7A
V5 = 12AT7

The 6C10 is a triple triode valve, so certainly can't be replaced with a 12AX7 unless the amp has been seriously modified. Maybe by omitting the reverb unit they've been able to do this, but the amp certainly isn't standard, and you don't know how well any modifications have been made.

The 6CX8 and the 6C10 aren't made any more, so you have to rely on a dwindling supply of NOS valves (which aren't cheap if you can get them), so I can see why someone made some changes. However, it isn't a proper Super Twin amp any more, so is worth what someone is willing to pay for what it is now. The big question is, were the changes made by someone who knew what they were doing and all the supporting resistors for the valves were changed to the right values so they work properly? You can't simply change valve types and expect them to do the same job without changing the supporting circuitry. Even the 12A_7 range (12AX7, 12AT7 etc.) aren't 100% compatible and the bias resistors for them need to be tweaked to get the best from them.

In the light of this, I wouldn't advise even powering it up, but it needs to go straight to an amp specialist who should be able to tell if it's safe to use and whether the modifications have been done correctly. If not, it could be lethal.

Also note that it needs a 4 ohm load (no alternate tappings are available), so a standard 4x12" cab will need to be modified so that all four 16 ohm speakers are wired in parallel.

DrNomis_44
18-03-2017, 09:30 AM
OK, bad news. Looking on the web for a schematic of the amp, one thing is certain - it shouldn't have three 12AX7s in it! http://acruhl.freeshell.org/mga/schematics/amps/supertwin.jpg

The valves should be:

V1 = 7052
V2 = 6CX8
V3 = 6C10
V4 = 12AX7A
V5 = 12AT7

The 6C10 is a triple triode valve, so certainly can't be replaced with a 12AX7 unless the amp has been seriously modified. Maybe by omitting the reverb unit they've been able to do this, but the amp certainly isn't standard, and you don't know how well any modifications have been made.

The 6CX8 and the 6C10 aren't made any more, so you have to rely on a dwindling supply of NOS valves (which aren't cheap if you can get them), so I can see why someone made some changes. However, it isn't a proper Super Twin amp any more, so is worth what someone is willing to pay for what it is now. The big question is, were the changes made by someone who knew what they were doing and all the supporting resistors for the valves were changed to the right values so they work properly? You can't simply change valve types and expect them to do the same job without changing the supporting circuitry. Even the 12A_7 range (12AX7, 12AT7 etc.) aren't 100% compatible and the bias resistors for them need to be tweaked to get the best from them.

In the light of this, I wouldn't advise even powering it up, but it needs to go straight to an amp specialist who should be able to tell if it's safe to use and whether the modifications have been done correctly. If not, it could be lethal.

Also note that it needs a 4 ohm load (no alternate tappings are available), so a standard 4x12" cab will need to be modified so that all four 16 ohm speakers are wired in parallel.


The wood cabinet that the amp chassis is in needs replacing with a new one because I noticed that the corner-joints are starting to come apart, good call about the 6CX8 and 6C10 valves, I didn't notice that, I'm going to wait till I've paid the guy the money I owe him for the amp before I go and do anything with it, I'm familiar enough with the safety procedures for working on valve amplifiers so I'll see if I can do the work myself, I'll certainly give it a good check out electrically to make sure it's electrically safe beforehand, that's for sure, I don't think I will sell the amp once it's all sorted out, I think I will keep it.

One thing I have noticed is that the standby switch definitely needs replacing because it appears to be stuck in the on position, the power switch seems good though, but I might just replace both as a matter of course, I think I can get a new knob for it from Evatco.


On the back panel of the amp chassis, near the speaker output socket, it says that the minimum load impedance is 4 Ohms.

billb
18-03-2017, 11:47 AM
Interesting, while I certainly don;t have the expertise of either of you two I do have an old Fender Studio Bass amp which is apparently pretty much the same basic amp as the super twin, minus a distortion control and at 8ohms - it certainly has the same valve set up as you found in yours so someone may have used it as the basis for refurb'ing yours?
If you can get it working properly, and if it sounds anything like the Studio Bass, you will NEVER sell it. (although to be fair you will also never actually move it as mine weighs well over 60kgs)
Here's some info you might find interesting for what you're doing:
https://www.talkbass.com/threads/fender-studio-bass-club.809269/
http://johnkvintageguitars.homestead.com/StudioBass.html
(last link has the schematic if you want it)

DrNomis_44
18-03-2017, 04:26 PM
So if I wanted to, I could mod it so that I could use it as a Bass amplifier?, that's interesting to know, if so, then I'd have something I could play my Squire P-Bass through, I'm assuming that I'd have to go through and change the value of some of the components to get the amp working well for a bass guitar, going by the preamp valves installed in the chassis, that's probably what it's previous owner did.

wazkelly
18-03-2017, 06:11 PM
Hi Doc, I think a lot of guitarists may have used Fender Bassman's for guitar last century as they had a bit more bottom & midrange and I did a similar thing with the ancient Marshall head I had. An amp tech back then had a look at it and compared the difference between it and a Golden Tone he was using at the time and the main differences were in the tone circuit. Not techy enough to remember exactly what but there was stuff all difference other than my old Bass head didn't have a master volume to help drive the pre amp section.

Simon Barden
18-03-2017, 10:25 PM
The previous owner (or the one before that) may have modified it to be quite a different amp to the original. There's a big difference between knowing how to work safely on valve amps and fully understanding their design and how they really work, so unless you are the latter, it really is worth getting your amp tech friend to have a look and see what mods have been made. Might be worth Googling to see if anyone has listed mods to the circuit to use 12AX7s, as if there's a schematic for that, it's probably going to be closer to that than the original schematic.

DrNomis_44
19-03-2017, 11:30 AM
Here's a thought, if for some reason I'm not able to restore the amp, what if I were to use some of the parts in it to build a Mesa/Boogie Mk I amp?, a Mesa/Boogie Mk I is basically a modded Fender amp (I think the original one was a modded Fender Princeton).

Simon Barden
19-03-2017, 10:55 PM
Very few parts you could usefully use. Most of (if not all) the capacitors would probably need to be replaced anyway as they will be well out of spec by now. Mains and output transformers will be incorrectly rated for a different amp. Valve bases will be ageing would best be replaced by new ones, though any that were undamaged could be re-used.

You might be able to re-use some of the resistors but they'd need to be of the correct value and wattage rating. No idea what sort of resistors they've used but if carbon comp types, they may be traditionally authentic but they are noisy and modern ones are far quieter. Plus if it's a PCB amp, then it's really not worth the effort of taking them off the old board. Obviously the valves can be re-used if they are still working OK (don't forget to take the 6L6s out in pairs and mark them up as such, as they will be matched).

DrNomis_44
23-03-2017, 03:16 PM
I just realized something, this Fender Super Twin amp is capable of producing almost as much power as the Marshall Major 200 Watt amps that Marshall used to manufacture, the Marshall Major 200 Watt amp was used by musicians like Mick Ronson, who used to be the guitarist in David Bowie's band(around the time of Ziggy Stardust), and also Ritchie Blackmore who played guitar in Deep Purple, the Marshall Major used four 6550 power valves, whereas my Super Twin uses six 6L6 power valves, I've found that I'm more of an EL34 power valve kind of guy, that is to say I'm more into the EL34 sound but I think it's cool to have another valve amp that uses a different type of power valve in your arsenal of amps to get different tones, the EL34 has that "British" tone, whereas the 6L6 has more of an American tone to it, but the actual tone you get will also be dictated by the circuitry that the valve is used in, or rather the topology of the circuit, Fender amps tend to use different component values in their tone control circuits compared to Marshall amps, what that means is that there is less of a midrange scoop in Marshall amps than there is in Fender amps, hence one of the reasons why Marshall amps tend to sound pretty loud.

DrNomis_44
29-03-2017, 06:49 PM
Update:


I just found out that Evatco do indeed stock the type of Fender knob I need for my Fender Super Twin amp, they look the same as the originals, but are numbered 0 through to 10, but that's fine with me.

http://www.evatco.com.au/product-list/knobs/k1-10/


I managed to find the serial number marked on the amp chassis, and it reads as follows:


B 17926

Did some googling and found this web page:


http://www.superiormusic.com/page195.htm


Apparently my Fender Super Twin was manufactured some time between 1975 and 1976, which makes it about 40 or so years old by my guess, I also found a metallic sticker on the back panel of the amp chassis, stating that at some point in the past it was serviced by a company called Soundworks Professional, I'm guessing that one of the company's service techs probably did the mods to the amp to allow the installation of the replacement 12AX7 valve when a 6C10 valve couldn't be sourced.

DrNomis_44
31-03-2017, 03:59 AM
Update:


Some good news for you guys, I have just managed to find my old Canon A480 Digital Camera, I'll see if I can get it working again so I can use it to take some better pics of the amp chassis insides once I've finished paying it off, so stay tuned.

DrNomis_44
04-04-2017, 05:26 PM
Update:

Some good news for you guys, I had a look at my old Canon A480 Digital Camera a few minutes ago, and it was displaying a low-battery icon even though the two batteries I had installed in it were brand new and measured good on my Digital Multimeter, anyway, the cause of the low-battery issue turned out to be very simple and easy to fix, one of the contacts in the battery compartment wasn't making a good enough contact with the battery terminal, to fix it I simply had to bend it up a bit, and now the camera seems to power-up normally....yay!!!

Even my computer seems to recognize the camera when it's plugged into a USB port, so, I'm pretty happy with that, will be able to take some better pics of the Super Twin amp for you guys to check out.

Update 2:

Just tried taking a couple of pics with the A480, all seems to work fine.

Simon Barden
04-04-2017, 05:57 PM
I just managed to fix an amp of mine that went noisily wrong just before a gig. It was the Fender Blues Deluxe that had been stripped out and the PCBs replaced by a hardwired turret board Fender 5E5-A circuit (40W Fender Pro) that I had mentioned above. It would be OK, then suddenly only produce a loud mains hum type noise. Seemed to be OK when starting cold, but then very soon switched into full-on hum mode. Checked for dry joints and damaged caps, but everything looked fine. It had a Weber Copper Cap rectifier (valve emulator) and I thought maybe that was the problem, as it seemed to be more 100Hz than 50Hz (and apparently reading the web, a failed rectifier can do that), so I had to order a new one from the US. But that didn't fix it. So in desperation I thought about what might cause a lot of hum and I then thought about the V3 phase-splitter valve. I had swapped the existing V3 valve out a while ago for a more balanced one that cured the background hum (The 12AX7 as you know is a dual triode and if the triodes have different gains then you get residual hum). So if one side wasn't working properly, then there would be a big gain mismatch and a lot of hum. Plus it was a fault that showed itself after the amp warmed up. So I swapped the valve out for another one and it all worked again (albeit with a slight hum). I hadn't come across a valve which worked for a bit and then didn't until now. They either worked OK or else behaved badly all the time.

So I ordered a new balanced valve yesterday, it came in the post today and it's all back to near-silent, with just some very gentle white-noise hiss. I had used it a couple of times with the speaker not plugged in for a few seconds before realising, and thought maybe I'd damaged the output transformer, but luckily this appears to be OK. Now just got to fit the Weber beam blocker (that I ordered as the same time as the Copper Cap rectifier) to the front of the speaker and I should have my gigging amp all set to go. Not too loud, not too heavy, great sound and hopefully no piercing beam of treble coming out of the front of the amp.

Simon Barden
04-04-2017, 05:58 PM
Good news on the camera front, Doc.

DrNomis_44
04-04-2017, 06:17 PM
I just managed to fix an amp of mine that went noisily wrong just before a gig. It was the Fender Blues Deluxe that had been stripped out and the PCBs replaced by a hardwired turret board Fender 5E5-A circuit (40W Fender Pro) that I had mentioned above. It would be OK, then suddenly only produce a loud mains hum type noise. Seemed to be OK when starting cold, but then very soon switched into full-on hum mode. Checked for dry joints and damaged caps, but everything looked fine. It had a Weber Copper Cap rectifier (valve emulator) and I thought maybe that was the problem, as it seemed to be more 100Hz than 50Hz (and apparently reading the web, a failed rectifier can do that), so I had to order a new one from the US. But that didn't fix it. So in desperation I thought about what might cause a lot of hum and I then thought about the V3 phase-splitter valve. I had swapped the existing V3 valve out a while ago for a more balanced one that cured the background hum (The 12AX7 as you know is a dual triode and if the triodes have different gains then you get residual hum). So if one side wasn't working properly, then there would be a big gain mismatch and a lot of hum. Plus it was a fault that showed itself after the amp warmed up. So I swapped the valve out for another one and it all worked again (albeit with a slight hum). I hadn't come across a valve which worked for a bit and then didn't until now. They either worked OK or else behaved badly all the time.

So I ordered a new balanced valve yesterday, it came in the post today and it's all back to near-silent, with just some very gentle white-noise hiss. I had used it a couple of times with the speaker not plugged in for a few seconds before realising, and thought maybe I'd damaged the output transformer, but luckily this appears to be OK. Now just got to fit the Weber beam blocker (that I ordered as the same time as the Copper Cap rectifier) to the front of the speaker and I should have my gigging amp all set to go. Not too loud, not too heavy, great sound and hopefully no piercing beam of treble coming out of the front of the amp.


That's a bit odd, I'm guessing that the 12AX7 valve that was suspect probably had an internal electrode connection-issue that was temperature-sensitive, something I've never come-across before, another possibility is that the cathode-emission could have gotten a bit low, but at least you managed to fix it in the end.

Simon Barden
04-04-2017, 06:26 PM
Yes, it seemed a bit weird to me as well, especially when it just switched modes rather than the hum gradually getting louder. At one point there were some loud 'clicks' before the full-on hum started, which normally indicate capacitors, so I wasn't thinking 'valve'. Something else I've learnt and can store away for future use.

DrNomis_44
04-04-2017, 06:42 PM
Yes, it seemed a bit weird to me as well, especially when it just switched modes rather than the hum gradually getting louder. At one point there were some loud 'clicks' before the full-on hum started, which normally indicate capacitors, so I wasn't thinking 'valve'. Something else I've learnt and can store away for future use.

I also would have been suspecting one of the contacts of the 9-pin valve socket that the suspect 12AX7 was installed in, sometimes the socket contacts can get a bit lose so that they just make contact enough to initially work, and then once the amp warms up the temperature disturbs the connection, this is all hypothetical, I seem to remember that some old Vox AC30 amps needed the valve pins to have a very light coating of oil to prevent corrosion.

What makes fault-finding in electronic equipment difficult is that the faulty component/s is not always obvious, I've even heard of some valves suffering from something called "Ion Migration" between the valve pins, this causes an electrical conduction-path between two valve pins where there shouldn't be any conduction.

DrNomis_44
06-06-2017, 05:54 PM
Update:

Went into uni today and met up with the guy who was selling the amp to me, and I gave him the money I owed him, so it's official, I fully own the Fender Super Twin amp now.

Marcel
06-06-2017, 10:38 PM
A decent tech should be able to reload your super twin with EL34's, but you'd loose some output power, most likely a 30% drop in power minimum.... sadly most techs these days don't have a clue particularly when it comes to tube amps.

I could do it if it could be freighted to me, but believe me when I say the freight and the modification would not come out the other end as a cheap exercise...!!.

My 50W Playmaster amp head that I just rebuilt from 6L6's to a 50W 2204 style EL34's based head has set me back close to AU$500 in industry sourced parts alone, everything replaced except the chassis, the tag strips and the transformers.....Considering that is without any labour charge (why would I charge myself for my own labour) but that does include all the tube sockets, switches, lamp, input jacks, caps, filter caps with mounts, resistors, diodes, filter choke, pots and a full set of 3 x JJ 12AX7's and 2 x JJ EL34's, then a project like yours if all goes well could easily double that purely on parts and then there is the labour charge on top.....

Really, Unless you have a lot of spare cash then changing your super-twin to EL34's is not an option worth considering... but there other things that can be done.....

DrNomis_44
06-06-2017, 11:24 PM
A decent tech should be able to reload your super twin with EL34's, but you'd loose some output power, most likely a 30% drop in power minimum.... sadly most techs these days don't have a clue particularly when it comes to tube amps.

I could do it if it could be freighted to me, but believe me when I say the freight and the modification would not come out the other end as a cheap exercise...!!.

My 50W Playmaster amp head that I just rebuilt from 6L6's to a 50W 2204 style EL34's based head has set me back close to AU$500 in industry sourced parts alone, everything replaced except the chassis, the tag strips and the transformers.....Considering that is without any labour charge (why would I charge myself for my own labour) but that does include all the tube sockets, switches, lamp, input jacks, caps, filter caps with mounts, resistors, diodes, filter choke, pots and a full set of 3 x JJ 12AX7's and 2 x JJ EL34's, then a project like yours if all goes well could easily double that purely on parts and then there is the labour charge on top.....

Really, Unless you have a lot of spare cash then changing your super-twin to EL34's is not an option worth considering... but there other things that can be done.....


The bloke I bought it from reckons that it still all works, I'm going to see if I can do a bit of restoration/maintenance work on in maybe later on this year or maybe next year, I'm looking at buying myself a brand new Fender USA Standard Stratocaster guitar from my local pro music shop so I won't be able to spend much money on the Super Twin amp till I've finished paying off the guitar, I will order a new Fender style knob for it from Evatco later this week, the cabinet needs the corners re-glued back together and it could do with some new Tolex, and corner protectors and etc, might also order some new preamp valves for it when I order the new knob, I think the six STR GC 6L6 valves are most likely still okay, none of them show any signs of gassing, the silver getter is still present in all of them.

DrNomis_44
07-06-2017, 07:48 PM
Update:

Finally found my Nikon Coolpix A100 Digital Camera, it was hiding in my Focusrite Scarlett Studio box of all places, turns out I had forgotten that I'd put it in there.....what a goose I am?...lol.....anyway, at least now I have two working digital cameras.


And now, I'm officially the new owner of the Fender Super Twin amp.

Marcel
08-06-2017, 04:33 PM
So, it's looking like I'll have to build myself a 400 Watt Dummy Load for testing the amp's performance once I get round to doing whatever restoration work on it that it needs to get it up and running again, I wonder where I could source a new combo cabinet for it from?, or, should I just keep it as an amp head and invest in a new 4 X 12 Speaker box?

It'll probably be good for annoying my noisy neighbors....heehee.....180 Watts of audio power.

I've built a few 'dummy loads' out of old style jug elements.... the ones which have coils of resistance wire wrapped around a porcelain block and has two brass rods holding the block suspended in the water. In their original form they are good for 1500W with 240VAC going in, but cut back down and rewound to 8 ohms and suspended in water they easily handle 800W RMS...

It was actually quite funny way back when to demo two of these loads to my electrician friends ... push 1kHz into an Jands 920 stereo amp, wind up to 450W RMS per channel (just short of clipping) and listen to the 2 cups of water squeal their way to boiling...

DrNomis_44
08-06-2017, 09:03 PM
Since my Fender Super Twin amp is missing a front panel that goes just under the chassis, I'm seriously thinking about making a new one, but instead of covering it with the usual Fender amp cloth, I'm going to try using a piece of Paisley patterned cloth, should make it look cool.

DrNomis_44
10-06-2017, 02:58 PM
Update:


I thought that I would do something cool and post a pic of the insides of the chassis of my Super Twin amp for you to check out, so here you go, this is what it looks like inside the chassis of one of these things, this is "Old School" Electronics where a good proportion of the components are mounted on Eyelet Boards, not Printed Circuit Boards, this is how Fender used to build their amps back in the day:

19955

dave.king1
10-06-2017, 03:10 PM
Thanks for the pic Doc, the wiring looks to be of an "interesting" standard.

From pics on the net I Don't Think Fender Done It This Way ( apologies to Waylon )

DrNomis_44
10-06-2017, 03:26 PM
Thanks for the pic Doc, the wiring looks to be of an "interesting" standard.

From pics on the net I Don't Think Fender Done It This Way ( apologies to Waylon )



Granted it does look a bit like a "rat's nest", I might see if I can tidy things up when I get round to doing the restoration work on it, the chassis definitely could do with a bit of a clean-out and service, I did spot one electrolytic cap that looked like it was on the way out.

DrNomis_44
12-06-2017, 03:41 PM
Update:

Did some googling for schematics for the Fender Super Twin and found that what I actually have is the non-reverb version, apparently there are two Super Twins that Fender used to manufacture, there's the Super Twin Reverb which uses a couple of unusual valves in the preamp, and then there's the Super Twin non-reverb which uses the same preamp circuit minus the reverb circuit, but is basically the same as the Super Twin Reverb, so, going by that, it's most likely that my Super Twin amp hasn't been modded but has had some electrolytic caps replaced, I haven't had a look inside the metal cover that's covering up all the main supply filter caps yet, this cover is sometimes referred to as a "Doghouse" by amp techs, this coming fortnight, I'll see if I can order a replacement Fender style knob for it and some new valves for my Legacy amp from Evatco.

Marcel
16-06-2017, 07:33 PM
Update:


I thought that I would do something cool and post a pic of the insides of the chassis of my Super Twin amp for you to check out, so here you go, this is what it looks like inside the chassis of one of these things, this is "Old School" Electronics where a good proportion of the components are mounted on Eyelet Boards, not Printed Circuit Boards, this is how Fender used to build their amps back in the day:

19955

OMG !!!.... Been a way long time since I've had to work on gear that looks that untidy, along with much fear that anything you touch might disintegrate...lol

... Probably doesn't look as bad in the flesh, but the photo sure brings out the worst of the cosmetic aspects of it...

DrNomis_44
16-06-2017, 08:25 PM
OMG !!!.... Been a way long time since I've had to work on gear that looks that untidy, along with much fear that anything you touch might disintegrate...lol

... Probably doesn't look as bad in the flesh, but the photo sure brings out the worst of the cosmetic aspects of it...


But in a funny and perverse kind of way, the insides of the chassis seems to be what really gets me excited, I guess old school electronics fascinates me for some reason that I don't quite understand.....lol.

Marcel
17-06-2017, 08:39 AM
I know where you are coming from on that...

There is a simplicity and a danger in tube gear that solid state just doesn't have. When you think of it nearly all tube gear gets their results with typically less than 10 active elements. Some how I think, and regardless of how it may sound or cost, we will never see the day where a solid state 50W 2204 style amp will ever be released boasting only 8 transistors.

Yeah, the danger is all pretty much the high voltages at potentially lethal currents. 500VDC @ 300mA in a guitar amp is more than enough to switch off a human life... and if working on that gives you a 'buzz' then maybe old school AM radio broadcasting repair might be worth a try where 6kVDC @ 700mA is quite common and 25kVDC @ 1.5A over two serious power tubes in series is often encountered, The thoughts of working anywhere near those voltages make some break into a severe nervous sweat, whereas others like myself it is our day-to-day job ... go figure...

Regardless of all that my heart just loves hearing a good tube guitar amp. 2nd harmonic and even overtones sound so much better when produced by real tubes than the filtered third and odd harmonic overtones that are the more natural condition of solid state. I suppose it is all a question of balance really....

DrNomis_44
17-06-2017, 05:20 PM
I know where you are coming from on that...

There is a simplicity and a danger in tube gear that solid state just doesn't have. When you think of it nearly all tube gear gets their results with typically less than 10 active elements. Some how I think, and regardless of how it may sound or cost, we will never see the day where a solid state 50W 2204 style amp will ever be released boasting only 8 transistors.

Yeah, the danger is all pretty much the high voltages at potentially lethal currents. 500VDC @ 300mA in a guitar amp is more than enough to switch off a human life... and if working on that gives you a 'buzz' then maybe old school AM radio broadcasting repair might be worth a try where 6kVDC @ 700mA is quite common and 25kVDC @ 1.5A over two serious power tubes in series is often encountered, The thoughts of working anywhere near those voltages make some break into a severe nervous sweat, whereas others like myself it is our day-to-day job ... go figure...

Regardless of all that my heart just loves hearing a good tube guitar amp. 2nd harmonic and even overtones sound so much better when produced by real tubes than the filtered third and odd harmonic overtones that are the more natural condition of solid state. I suppose it is all a question of balance really....


I think part of my fascination with Tube/Valve technology is that I'm tired of trying to work with components that require a magnifying glass and a pair of tweezers just to read the component values and solder them onto circuit boards, I prefer working with components that I can easily hold in my hands and read without squinting my eyes, I've found that in reality, surface-mount devices are not more reliable than conventional components, but if other people like SMD technology well then each to their own.

When a Valve amplifier distorts, or is overdriven, as you have said, they do generate even order harmonics, and they definitely do sound more musical, to my ears the difference between an overdriven Valve amp and an overdriven Solid-State amp shows up as a high-frequency crackling when a Solid-State amp is overdriven, a Valve amp sounds a lot smoother to my ears, it has a fuzziness in the high-frequencies, plus the distortion harmonics tend to be mostly in midrange and upper midrange frequencies, but the overall tone is more determined by the circuit-topology of the amplifier, my Marshall MA100C is an all Valve 100 Watt amplifier and the signal-path is all through Valves from the input through to the output, there is some solid-state circuitry but that's mainly for channel-switching, reverb, and the resonance control which affects the low end in the amps power-amp section.

And it's true, for a basic Triode gain-stage you need less passive components to get it working correctly than you need for an equivalent Bipolar Transistor gain-stage, you only need three fixed resistors to get a Triode gain-staged biased correctly, whereas a single Bipolar-Transistor needs four, yes there is the Fet (Field Effect Transistor) which is like a Solid-State equivalent of a Triode, but in actual fact, the Fet behaves more like a Pentode.


If you do know what you are doing and follow the correct electrical safety procedures then Valve amps can be safe to work on, provided that you keep your head screwed-on.

Marcel
17-06-2017, 09:01 PM
Amen to everything you wrote Doc...you are preaching to the converted...lol

All my tube knowledge basics (and a lot of what I know about electronics) I learnt back in the early '70's. To get out of the Melbourne winter cold I joined the schools ham radio club. It is amazing what sinks in to a young teenage mind when you overhear doctorate professionals giving an in depth Amateur radio training course on the subject at a time when tube technology was still regarded as 'current' and the 2N3055 and the NE741 were the new kids on the block...

As for SMD.... try playing with that stuff on 10GHz or 15GHz where true 'White man magic' starts to happen and everything below 1GHz seems to behave like DC by comparison ...

I have similar to you with my JVM210c. 100W 2x12 combo with bucket loads of gain on an all tube signal path and solid state switching and digital reverb. It is certainly more amp than my meagre guitar playing deserves...

DrNomis_44
18-06-2017, 12:23 AM
Amen to everything you wrote Doc...you are preaching to the converted...lol

All my tube knowledge basics (and a lot of what I know about electronics) I learnt back in the early '70's. To get out of the Melbourne winter cold I joined the schools ham radio club. It is amazing what sinks in to a young teenage mind when you overhear doctorate professionals giving an in depth Amateur radio training course on the subject at a time when tube technology was still regarded as 'current' and the 2N3055 and the NE741 were the new kids on the block...

As for SMD.... try playing with that stuff on 10GHz or 15GHz where true 'White man magic' starts to happen and everything below 1GHz seems to behave like DC by comparison ...

I have similar to you with my JVM210c. 100W 2x12 combo with bucket loads of gain on an all tube signal path and solid state switching and digital reverb. It is certainly more amp than my meagre guitar playing deserves...


I've been into Electronics as a hobby since I first started when I was 13 years old, I'm 47 years old now, turning 48 in August this year, I'm mostly self taught in Electronics but I did do some formal studies in the mid 90's at my local University, I've got lots of build projects in my head that I would love to do, you may have seen my DIY Valve Amp Head thread in the Pitbull Guitar Amps section, haven't been able to order the bits I need to do some more work on it this year so far, had other things I needed to put my money into, but hopefully later on this year I'll be able to do more work on it, I do happen to have some test equipment like a Signal Generator, a good 20Mhz Dual-Trace Oscilloscope, some good Multimeters, a couple of good temperature controlled Soldering Stations, but I'll need to design at least one good Dummy Load for testing/biasing guitar amps, this whole Electronics hobby thing is a fun learning experience, and so far I've enjoyed it a lot.


One thing I would love to learn is how to design a good sounding speaker cab for musical instrument amplifiers, I've got a great book lying around somewhere that's got all the theory and stuff in it about designing speaker cabs, it's mostly geared towards Hi Fi speakers but the underlying principles are the same, the book is written by a guy called Vance Dickason, and you can buy it from your local Jaycar Electronics shop, I've got another book called Build Your Own Audio Valve Amplifiers, which is written by another guy called Rainer Zur Linde, Jaycar Electronics also sell this book, it's mostly geared towards Hi Fi Audio Valve Amplifiers but there is a section on Guitar Amplifiers in it too, there's also a great project for a Stereo Hi Fi Valve Preamp and there's also PCB artwork included too if you want to etch your own PCBs, pretty cool, I'm seriously thinking of building one one day once I can get all the parts I need, other pieces of Valve equipment I'm seriously interested in building are a set of four Gyraf Audio Valve Preamps for my little bedroom studio, but I need to source some Lundahl input and output transformers for them first though, and they are not cheap.

Here's a link to the Gyraf Audio website, some really cool stuff on it:

http://gyraf.dk/


The Gyraf Audio Valve Preamp I'm interested in building can be found amongst the DIY projects, it's called the G9 Mic Preamp.

Marcel
18-06-2017, 08:52 AM
Wow... lots of good stuff on the Gyraf site... And that G9 preamp would be quite fun and challenging to build...

Much the same here... Got into radio in year 7 by joining the school radio club in '73. Radio tech in the RAAF until '86, Roadie work for a while and played Audio tech at Brisbane Expo 88, Wanted a real job so worked as a tech for radio and TV stations then moving on into aviation electronics for a few years, now after collecting all the tickets and licences I need to hold I'm back as private contractor tech for commercial radio... I'm 55 now and collected heaps of junk and test gear over the years that all sits gathering various amounts of (wood) dust in my 9mx12m shed that also doubles as my luthery workshop that was setup mostly to help recover from a heart condition...lol

It's all good.... Like everybody, I know a bit about some things and not much about others...

FrankenWashie
18-06-2017, 10:31 AM
He he I hear you with that last statement Marcel. I know enough about Electrickery to get myself in trouble and have become wise enough over the years to know when to stop fiddling to avoid real trouble.

I hope the ticker troubles are behind you now.

Marcel
18-06-2017, 10:38 AM
I saw my local GP last week to go over the results from my most recent CT scan, and in his words "What ever you are doing keep doing it!" and he then promptly wrote out an Okay to go back to work.... So I figure I'll keep building guitars in my spare time ...lol

FrankenWashie
18-06-2017, 10:41 AM
Good to hear its all okay, and that you can go back to work. Just not working too hard eh ;)

DrNomis_44
18-06-2017, 11:19 AM
@ Marcel That's good to hear mate, last time I had my blood pressure measured the Doctor said that it was fine, and the last time I had my eyesight tested by an Optometrist they said that it wasn't deteriorating, technically I should be wearing my glasses as I was born Short-Sighted, but I can actually see well enough without them to be perfectly able to cross the road safely.

Marcel
18-06-2017, 03:38 PM
6 months ago I collapsed in a exhausted heap after taking a simple regular shower. They subsequently diagnosed me with what amounts to a DVT in my chest right next to my heart.... so for the past 6 months they put me on a controlled and monitored diet of modified rat poison which surprisingly has actually worked to clear the DVT. Side effect has been to turn me into a real Aussie bleeder so playing with sharp knives has been a no-go for me. The upshot of no pointy knives means I've become a real whiz at cutting almost anything with side-cutters...lol

What this thing 'hard work' you speak of ??? ... Is it something you dream of ???

FrankenWashie
18-06-2017, 04:54 PM
6 months ago I collapsed in a exhausted heap after taking a simple regular shower. They subsequently diagnosed me with what amounts to a DVT in my chest right next to my heart.... so for the past 6 months they put me on a controlled and monitored diet of modified rat poison which surprisingly has actually worked to clear the DVT. Side effect has been to turn me into a real Aussie bleeder so playing with sharp knives has been a no-go for me. The upshot of no pointy knives means I've become a real whiz at cutting almost anything with side-cutters...lol

What this thing 'hard work' you speak of ??? ... Is it something you dream of ???

Lately its been my recurring waking nightmare...Luckily I have guitar building to occupy my brain with more pleasant things.

Marcel
19-06-2017, 07:55 AM
Speaking of hard work made easy...

Have you ever considered getting an amp kit from these guys Doc??

https://www.tubedepot.com/t/diy-central/kits-tube-amp

DrNomis_44
19-06-2017, 04:58 PM
Speaking of hard work made easy...

Have you ever considered getting an amp kit from these guys Doc??

https://www.tubedepot.com/t/diy-central/kits-tube-amp


Yep, been seriously wanting to order a JTM45 kit from that company for a long time, just haven't been able to get together the money for one, maybe that might be a good project for next year, I'd either go for the JTM45 + or the JTM45 combo kit, the other kits look really nice too.

Marcel
19-06-2017, 06:54 PM
My preference if I had the spare money to get one is for the British 18W style combo. Has a pair of EL84's on the output and comes with a Celestion G12M Greenback... My kind of combo ...

Not keen on their JTM45 kits as they have made changes to their kit circuit which are not in the published Marshall designs. I suppose the changes could be undone but as I already have my 2204 clone build the desire has waned substantially.

Maybe it's just me but I prefer the British EL34 or EL84 grunge sound over the American 6L6 or 6V6 cleans. Probably why I have built my 2204 clone and own a real Marshall JVM210c, and only ever fixed other peoples Fender amps.

DrNomis_44
29-06-2017, 10:58 PM
One of the thing that needs doing to my Fender Super Twin amp is that the sockets for the six STR 6L6 Valves need replacing since they seem a bit loose, or the valve retainers seem loose anyway, I could go with a set of Ceramic Octal sockets with Spring-Retainers, the sockets for the preamp valves could either be kept or maybe replaced with new Ceramic 9-pins too, I might just go the whole hog and replace all the original sockets with new Ceramic ones as a matter of course, the power and standby switches definitely need replacing as they tend to stick a bit.

Seeing as I have a Marshall amp and the Fender Super Twin, I've got an amp with EL34 valves and an amp with 6L6 valves, the best of both worlds so to speak, I found that I'm mostly an EL34 guy, but, having said that, I'm not afraid to show my appreciation for the 6L6 sound, variety is the spice of life, my mate reckons that with the two amps I have the two basic food groups of tone.

Also I just remembered that I have a spare 6V6 valve in a white box somewhere, I'm thinking of pairing it up with a 12AX7 valve or a 7025 valve and making a DIY Fender Champ at some stage, I'd probably need to source a good 5Y3 Rectifier valve, or go with solid-state rectifiers, seeing as Evatco sell valves and other amp parts, I might be able to source a good 5Y3 from them, anyway, that's a future project.

I could even go with a 5U4GT rectifier too if I could source one.

Marcel
30-06-2017, 04:00 PM
There are heaps of places to get bits there Doc.

I find Ebay is often quite reasonable, but sometimes you do need to do some hunting around... For most electronic bits I usually try these Australian Online sites first...
RS components - http://au.rs-online.com/web/
Jaycar - https://www.jaycar.com.au/
Element14 - http://au.element14.com/

The two Ebay sellers below I have bought from have been quick delivery and have a reasonable variety of stuff. Think both have 5Y3's in stock..
Vicmazz - https://www.ebay.com.au/sch/vicmazz64/m.html?_nkw=&_armrs=1&_ipg=&_from=
Amptubes - https://www.ebay.com.au/sch/amptubes/m.html?_nkw=&_armrs=1&_ipg=&_from=

There are plenty of others (mostly Asian) that have similar and often cheaper stuff however often they only sell in quantities of 100 or more. That's way too many tube sockets for my needs... one site I got 3 Chinese made 12AX7/ECC83's for AU$32 which is pretty damn cheap.

I'm keen to build a EL84 amp... something akin to a Vox AC15... but that will have to wait until I get all my guitar builds done...

DrNomis_44
01-08-2017, 05:54 PM
Update:

Went to my local Jaycar Electronics shop today and bought some red and black coloured banana plugs, some red and black alligator clips, and some red and black wire, these are for making a set of new test leads for my ESR Meter and the component tester on my 25Mhz Dual-Trace Oscilloscope, I think I'm going to be needing them when I finally get round to doing some servicing work on my Fender Super Twin amp, will be making the new test leads tomorrow.

Marcel
02-08-2017, 06:57 PM
Don't make your ESR leads too long. I've found 10cm to 15cm is usually plenty long enough. This is especially true for your capacitance meter as the stray stuff from leads will give you wildly false readings on the smaller value caps.

DrNomis_44
02-08-2017, 08:18 PM
Don't make your ESR leads too long. I've found 10cm to 15cm is usually plenty long enough. This is especially true for your capacitance meter as the stray stuff from leads will give you wildly false readings on the smaller value caps.


Good point, although it's probably not going to affect the component tester on my 25Mhz Dual Trace Oscilloscope, it's one of those old school ones with a Cathode-Ray display tube in it, the component tester in the Scope uses the X/Y function to draw a straight-line, or elliptical shape on the screen for a basic go/no-go test result display, it's good for quickly testing semiconductor devices out to see if they're good or not, I'll post a pic of my Oscilloscope later on, but yeah I'll keep that in mind, cheers mate.

Marcel
03-08-2017, 05:10 AM
I have a hand held LC meter which I use to check various coils and caps. You have seen it in earlier photos.

I also have a set of 10cm leads for it for the bigger stuff, plus a very useful and accurate little PC board with 2 pins spaced the meters terminal width apart and a slot cut between the 2 copper halves so I can check surface mound bits. It gives accurate measurements as it has near zero lead length.

DrNomis_44
02-11-2017, 05:57 PM
Update:

I've been doing some testing of the original preamp Valves that were installed in the sockets of my Fender Super Twin's chassis, I tested them by plugging them into the 9-pin socket of my Baja Real Tube Overdrive pedal, and also the preamp sockets of my little Legacy 5 Watt valve amp, one thing I did notice is that they all sounded a bit weak in gain, taking into account that the 12AT7 and 12AU7 are lower-gain twin triodes, so, I'm assuming that they are all getting a bit worn-out.

I've had a look through Evatco's stock of preamp tubes and have decided to go with a set of new JJ brand valves as replacements for all of them, here's a list of the stock preamp valves and their replacements:


V1: 7025, being replaced with a new JJ 12AX7/ECC83S Gold Pin.

V2: 12AU7, being replaced with a new JJ 12AU7/ECC82.

V3: 7025, being replaced with a new JJ 12AX7/ECC83S Gold Pin.

V4: 12AX7A, being replaced with a new JJ 12AX7/ECC83S Gold Pin.

V5: 12AT7, being replaced with a new JJ 12AT7/ECC81.


I may even go ahead and replace all the original valve sockets too, the sockets for the six 6L6 power valves do seem to be a bit loose, so maybe a set of new ones will do the amp some good, might also get some new spring retainers while I'm at it.


Might also be worth having a look under the doghouse cover and see if any of the supply filter caps need replacing with new ones.

Guvna19
02-11-2017, 06:44 PM
any pics please Doc?

DrNomis_44
02-11-2017, 06:59 PM
any pics please Doc?


You mean pics of the amp?, I've already posted some in this thread a few pages back.

Marcel
02-11-2017, 07:51 PM
I'd have thought you'd build yourself a little tube tester in a die cast box to confirm or deny your tubes, but I suppose the Baja pedal does the same thing.

As most measurements would be DC based they can be pretty simple fixed resistor units with banana sockets for metering points. A fixed self bias for the smaller tubes maybe with a optional capacitive audio in/out is easy to implement, Larger tubes are an issue for current draw and fixed bias but it's not beyond the realms of possibility if you use reasonable sized VA transformers.

On the subject of transformers I am considering a purgatory pedal build powered by a 12VAC plug pack and having a 240:12V 3VA transformer to create the HT which I calculate should be plenty for one 12AX7, so using similar for a test box should be easy.

DrNomis_44
02-11-2017, 11:43 PM
I'd have thought you'd build yourself a little tube tester in a die cast box to confirm or deny your tubes, but I suppose the Baja pedal does the same thing.

As most measurements would be DC based they can be pretty simple fixed resistor units with banana sockets for metering points. A fixed self bias for the smaller tubes maybe with a optional capacitive audio in/out is easy to implement, Larger tubes are an issue for current draw and fixed bias but it's not beyond the realms of possibility if you use reasonable sized VA transformers.

On the subject of transformers I am considering a purgatory pedal build powered by a 12VAC plug pack and having a 240:12V 3VA transformer to create the HT which I calculate should be plenty for one 12AX7, so using similar for a test box should be easy.


I would have built myself a Tube Tester but unfortunately i don't have the parts needed nor the money to buy them, so I used my Legacy amp and Baja Real Tube Overdrive pedal as the next best things, i must put building a Tube Tester on my "to do" projects list.

Marcel
03-11-2017, 08:12 AM
Yep, It's funny how we have nil problem on spending a few hundred of the hard earned on a new guitar or a new set of wheels or a few bottles of our favourite plonk, but diverting a fifty to some useful test equipment is 'a big decision'.... I know that problem well, and have the T-shirt... ;)

DrNomis_44
03-11-2017, 10:14 AM
Yep, It's funny how we have nil problem on spending a few hundred of the hard earned on a new guitar or a new set of wheels or a few bottles of our favourite plonk, but diverting a fifty to some useful test equipment is 'a big decision'.... I know that problem well, and have the T-shirt... ;)


Yep, since I'm a pensioner my fortnightly budget tends to be pretty tight too, so I can only buy things when I can afford them, fortunately my big purchases for this year have mostly been done, I've got some big purchases to make next year too, need to buy a replacement TV cause my 42 inch LG Plasma Screen TV no longer powers up, and my LG Blue Ray DVD player appears to be malfunctioning too, had to buy a replacement remote for it only to find that it doesn't seem to be responding to the remote, it also occasionally displays an error message too.

When I got offered the Fender Super Twin amp for $300.00, I thought that the offer was too good to refuse, since to buy one on eBay or somewhere else would cost me way more money, so naturally I couldn't pass it up.

Marcel
03-11-2017, 09:44 PM
I did a search on Ebay and only one USA version (110VAC) is listed for five times what you paid. Everything else listed is just parts... Damn expensive parts!!

From my cloudy memory (the joys of age I suppose) most of the amps I worked on were Fender twin combo's and a handful or so of VOX amps. Even though back then I was a authorised Marshall agent in a workshop above a Brisbane Marshall store (walking distance to the Roxy in the Valley) I had very few Marshall's cross my bench, so I'm guessing the 'other tech' in Paddington got most of the Marshall work as he could hot-rod them whereas as and agent I wasn't permitted. The other guy was the Fender agent so I got to hot-rod all the Fender amps...

I'm gathering you are still mid way through the twins 'repair'...?

DrNomis_44
08-11-2017, 12:20 PM
I did a search on Ebay and only one USA version (110VAC) is listed for five times what you paid. Everything else listed is just parts... Damn expensive parts!!

From my cloudy memory (the joys of age I suppose) most of the amps I worked on were Fender twin combo's and a handful or so of VOX amps. Even though back then I was a authorised Marshall agent in a workshop above a Brisbane Marshall store (walking distance to the Roxy in the Valley) I had very few Marshall's cross my bench, so I'm guessing the 'other tech' in Paddington got most of the Marshall work as he could hot-rod them whereas as and agent I wasn't permitted. The other guy was the Fender agent so I got to hot-rod all the Fender amps...

I'm gathering you are still mid way through the twins 'repair'...?


Actually no, I haven't even started working on it, still in the "planning" stage, I did make some progress on the 4X10 speaker cab though, I was doing some browsing through Evatco's stock of Jensen speakers a few days ago and came across a likely candidate for a Jensen speaker to put in the new cab, it's this model:

https://www.evatco.com.au/jbb10-100


I figure that four of them wired in series-parallel like a Marshall cab should effectively give me an 8 Ohm 4X10 cab that's rated at 400 Watts if my calculations are correct, the only kicker is the price of the speakers at about $339.00 each....(yikes!), I really want to go with a set of four Jensens cause I think the amp deserves them, although I could go with Eminences or EVs.

Marcel
08-11-2017, 04:07 PM
You suffer from the same syndrome as me...always want the most expensive one.... lol

There are plenty of other Jensen's at Evacto for a lower price, and a lower wattage. I suppose it depends on how much you desire that 400W capability.

Are you building a sealed or open back cab for your 4x10's?

My 2x12 cab has a V30 at 65W and a G12H75 at 75W with both 16 ohm speakers wired in parallel to give me a 8 ohm cabinet that can handle better than 100W which is all I figure I'll ever need. Two 16's in parallel is brighter than two 8's or 4's in series, plus there is a redundancy aspect of a parallel cab and I like the sound of the Celestions so that's my reasoning for going that way.

DrNomis_44
08-11-2017, 04:57 PM
You suffer from the same syndrome as me...always want the most expensive one.... lol

There are plenty of other Jensen's at Evacto for a lower price, and a lower wattage. I suppose it depends on how much you desire that 400W capability.

Are you building a sealed or open back cab for your 4x10's?

My 2x12 cab has a V30 at 65W and a G12H75 at 75W with both 16 ohm speakers wired in parallel to give me a 8 ohm cabinet that can handle better than 100W which is all I figure I'll ever need. Two 16's in parallel is brighter than two 8's or 4's in series, plus there is a redundancy aspect of a parallel cab and I like the sound of the Celestions so that's my reasoning for going that way.


Yep, I want to build a sealed-back 4X10 speaker cab for the Super Twin.

DrNomis_44
17-12-2017, 10:20 AM
Update:


Was doing some internet browsing and found this web page, the Fender Super Twin amp you see in the pic is same like the one I have, so if it makes a great bass amp then I'm keeping it for sure, it was a keeper for me anyway though:

https://www.talkbass.com/threads/fender-super-twin-bass-head.452093/

Marcel
17-12-2017, 12:59 PM
Very nice...

I have a feeling in my gut that says your Eminance loaded 4x10's won't sound the same as the dude's JBL loaded 2x15's.... just sayin... ;)

dave.king1
17-12-2017, 07:10 PM
I prefer 10s for bass as they are usually tighter than 15s or 18s and don't flub as much.

Having said that we are different and seek our own sound, so what ever rows your boat.

Given that decent speakers cost a bomb I be trying to scam the use of a few alternative speaker combinations before draining the piggy bank

stuzl873213
17-12-2017, 07:37 PM
Are the valves readily available?

Marcel
17-12-2017, 07:45 PM
Yeah, The whole Flubby thing doesn't suit most situations...

I've always just been a fan of JBL speakers in general, particularly in the control room situation as I know what I can expect out of them .... Not everyone's cup of tea, but it is why I own two sets of JBL Control 1 monitors.
On a guitar I lean strongly toward the usual crowd of Celestions, and with bass I have a huge preference for the economically priced 350W Eminence Delta 10A's...

DrNomis_44
17-12-2017, 11:45 PM
Are the valves readily available?


Yep, 6L6 GCs are still available, as well as the 7025/12AX7WA, 12AX7, 12AT7, and 12AU7, I wonder if a set of 6L6STRs would work in a Fender Super Twin too, I think they may have good enough ratings for the job.

Marcel
18-12-2017, 05:47 AM
Yep, 6L6 GCs are still available, as well as the 7025/12AX7WA, 12AX7, 12AT7, and 12AU7, I wonder if a set of 6L6STRs would work in a Fender Super Twin too, I think they may have good enough ratings for the job.

Plenty of Fender amps came stock fitted with 6L6's, so most varieties should work well. You won't know for sure unless you give them a try...

DrNomis_44
20-01-2018, 04:18 PM
Here's a closeup shot of one of the 6L6 power tubes from my Fender Super Twin amp, from what I can make out by looking at it through a magnifying glass, it says "STR415 Mesa Engineering" on the glass envelope:

24305


What does seem a little strange is that the glass envelope seems to be a bit shorter than most of the 6L6 tubes I've seen on the internet.


Here's a closeup shot of the Fender Super Twin's back panel where the speaker out socket is located:

24306


That socket labeled "Line/Recording" is going to be useful since I can connect a D.I. box up to it and send a signal out to a P.A. mixing desk in a live band scenario.

Marcel
20-01-2018, 04:53 PM
For their plate dissipation 6L6's are quite a short tube, and EL34's are quite long.

I've never had much faith in the "line/recording" socket on most amps. Mostly as so much depends on the volume level that is being used on the amp at the time you want to pull a signal from that socket. If the guitarist cranks the amp you get heaps of level, maybe too much, and if the guitarist winds things back then the console operator is hunting for gain on their desk due to the piddly tiny signal from the socket all while screaming out for their SM57. They can work but success can be hit or miss...

Simon Barden
20-01-2018, 06:20 PM
Also there's no speaker emulation, so unless you keep things clean (and use a fair bit of EQ on the desk), any overdrive or distortion is going to sound very fizzy indeed, as you don't have the natural low-pass filtering effect of the speakers

It's probably best used for feeding another amp for more volume that has series effect send and return sockets and plugging it into the return, so it can drive the 2nd amp's power section directly.

The STR 415 might be a badged Phillips valve (or a copy of), in which case it's specified like a 7581a (35 watts), as opposed to the 6L6 (30W rated) STR-387 also used by Mesa.

DrNomis_44
21-01-2018, 01:42 PM
Maybe I can do some mods to the recording line out socket to make it more useable in a live situation....hmmmmm....food for thought, I have a feeling that this thread is going to be another epic one like the one for the Gold Strat.

Simon Barden
21-01-2018, 05:31 PM
You'll probably do better by simply buying a speaker emulator pedal. As well as a low pass filter to emulate the natural HF roll-off of a 12" speaker, you'd also need to try and emulate the EQ effect of the speaker's frequency dependent impedance curve (which is itself modified by the type of enclosure it's in). The trouble is that a guitar speaker normally has a very steep roll-off typically somewhere between 5kHz -6kHz, but drops by around 20dB and then levels off again (normally just radiations from the centre dome). So a LP filter alone removes too much high-end for realism, so you also need an attenuated (around -20dB) filter bypass path to mix some of that high frequency signal back in again.

Marcel
21-01-2018, 06:08 PM
There are plenty of calculators available via Google to work out what you need to make a passive filter to emulate a speaker....

One I thought might be worth a try is at http://www.calculatoredge.com/electronics/bw%20pi%20low%20pass.htm

Put in the impedance and number of stages and the calculator does the rest..... 600 ohm for line level or 8 ohm for speaker level, and more stages gives a steeper slope. May not be ideal, plenty to experiment with and worth a try...

moody
29-01-2018, 11:06 AM
Update:


Was doing some internet browsing and found this web page, the Fender Super Twin amp you see in the pic is same like the one I have, so if it makes a great bass amp then I'm keeping it for sure, it was a keeper for me anyway though:

https://www.talkbass.com/threads/fender-super-twin-bass-head.452093/


I haven't posted here in a while but came around as I am getting back to finishing my kit bass.

If you look further down in that thread I have a post in 2008.

It is a superb bass amp. Mine needs some repair at the moment (fuzziness in the preamp somewhere). Do not touch the distortion control as it sounds awful.

It needs no modding aside from turning it into a head for use with bass.

moody
29-01-2018, 11:06 AM
Oh, and don't bother with the line out. You're better off with a mic, a di or both.

DrNomis_44
29-01-2018, 01:34 PM
I haven't posted here in a while but came around as I am getting back to finishing my kit bass.

If you look further down in that thread I have a post in 2008.

It is a superb bass amp. Mine needs some repair at the moment (fuzziness in the preamp somewhere). Do not touch the distortion control as it sounds awful.

It needs no modding aside from turning it into a head for use with bass.


Yeah I've read a lot on the internet where most owners reckon the Super Twin's built-in distortion was basically rubbish, it's already in a wooden cabinet for a Fender Bassman head so I don't have that much work to do with regards to getting a cabinet for it, the existing cabinet does need all it's corner joints re-glued cause they're a bit loose, it could do with some re-tolexing too as well as some new chrome fittings and maybe a new handle, I'm going to see if I can get all the new preamp tubes ordered from Evatco tomorrow, plus a few other things too.

DrNomis_44
03-07-2018, 03:09 PM
Update:

Okay it's time for an update, I've been looking at buying a speaker cab, and building one myself, it turns out that both options are going to cost me a bit, recently, I was in my local Cash Converters shop doing some browsing, when I noticed that they had an Ashton GA-100 Amp Head and Quad Box in stock, anyway, I waited till today to go and see if they were both still in stock and they were, what's more, they were being sold separately, the Ashton Quad Box was going for $450.00, so I decided to put it on layby, I put $200.00 on it and only have another $250.00 left to pay off, the people at Cash Converters are giving me 3 months to pay it off.

I googled the specs for the Ashton Quad Box and it turns out that it can handle 200Watts of power, impedance is 8 Ohms, and has four Celestion Rocket 50's in it, the Ashton GA-100 Head and Quad Box looked like the one in the pic below:

27235

Marcel
03-07-2018, 03:54 PM
It's Karma that the cab was destined for you Doc... Sitting there patiently waiting for you to put it on layby...

DrNomis_44
03-07-2018, 10:04 PM
It's Karma that the cab was destined for you Doc... Sitting there patiently waiting for you to put it on layby...


Or, it was tempting me to buy it by whispering sweet nothings in my ear subliminally, which is probably more the case....lol.


I'm thinking that, if it all works out, pairing the Ashton Quad Box with my Fender Super Twin is going to result in a killer guitar rig, especially for doing Surf Rock tunes, if I need some overdrive tones I'll be able to add a distortion pedal to the mix, since the Super Twin should take pedals pretty well, the Super Twin also has a 5-band foot-switchable EQ built in so that should be pretty useful.

wazkelly
04-07-2018, 07:10 PM
They will be able to hear you playing over in East Timor with that setup.

DrNomis_44
04-07-2018, 10:50 PM
They will be able to hear you playing over in East Timor with that setup.


Haha...yeah, that's exactly the point....lol.


Once I get the quad box home from Cashies, I'll be sure to post a pic of it with my Fender Super Twin amp perched on top of it for all of the forum members, I'm sure everyone will be interested in checking it out, might record a demo of it connected up to my Marshall amp too.

DrNomis_44
29-07-2018, 05:32 PM
Update:

I've organized things with a good mate of mine to pick up the Ashton Quad Box from Cash Converters on Tuesday next week after uni, feeling pretty excited about it since it means I can finally start making some serious progress on getting the Super Twin amp up and running, ready for gigging.

Will post a pic of it once I get it home.....stay tuned.

DrNomis_44
31-07-2018, 03:42 PM
Update:

Woohoo!!!!......guess what?.....the Ashton quad box is finally here in my new flat!!!


Here's a pic of it with my Fender Super Twin amp sitting on top of it for you to check out, I'm calling it my Big Rig:

27622

Marcel
31-07-2018, 04:23 PM
Time to let the neighbours know you're a guitar man...??

DrNomis_44
31-07-2018, 04:32 PM
Time to let the neighbours know you're a guitar man...??


Lol....yep, revenge will be sweet....*cue long, drawn-out evil laugh*

Dedman
31-07-2018, 08:06 PM
https://www.youtube.com/watch?v=7edeOEuXdMU

DrNomis_44
31-07-2018, 08:53 PM
https://www.youtube.com/watch?v=7edeOEuXdMU


Now picture that scene extended by, oh, 100 hours, now that's an evil laugh....lol.


Just out of curiosity, I had a quick peek at the insides of the quad box by shining a torch through a gap in the back baffle, inside it, I saw four rear-mounted Celestion G12E-50 Rocket 50 speakers.

FrankenWashie
01-08-2018, 06:47 AM
Now picture that scene extended by, oh, 100 hours, now that's an evil laugh....lol.


Just out of curiosity, I had a quick peek at the insides of the quad box by shining a torch through a gap in the back baffle, inside it, I saw four rear-mounted Celestion G12E-50 Rocket 50 speakers.

Oh bugger, you'd best send it back then eh Doc!?

DrNomis_44
01-08-2018, 01:53 PM
Oh bugger, you'd best send it back then eh Doc!?


Nah, it's a keeper, Celestions are good speakers.

Simon Barden
01-08-2018, 03:49 PM
Celestions are honest speakers, (so will handle a true 50W, unlike some other speaker brands) but not all are great. Those ones are definitely built to a low price-point. At 95dB, it's not the loudest speaker out there (though probably a benefit with a 200W amp) so don't be surprised if the amp doesn't sound as loud as you think it should. https://celestion.com/product/20/rocket_50/

The trouble with a quad-box is that it costs such a lot to upgrade all the speakers.

DrNomis_44
01-08-2018, 11:14 PM
Celestions are honest speakers, (so will handle a true 50W, unlike some other speaker brands) but not all are great. Those ones are definitely built to a low price-point. At 95dB, it's not the loudest speaker out there (though probably a benefit with a 200W amp) so don't be surprised if the amp doesn't sound as loud as you think it should. https://celestion.com/product/20/rocket_50/

The trouble with a quad-box is that it costs such a lot to upgrade all the speakers.


I guess the Ashton quad box I bought is better than nothing at all, at least I know it is working perfectly with no rattles or distorted sound from the speakers, I may end up upgrading the speakers at a later date, but for the time being they're fine.

Now that I've got the speakers sorted out, I can turn my attention to the amplifier itself, I have been doing my best to resist the urge to try the amp out with the quad box because I want to be 100% sure that the amp is totally electrically safe, I really don't plan on dying from a 500V DC shock any time soon, one thing I definitely need to do is replace the stock 3-core mains cabling, if I was doing an electrical Tag and Test on it I'd fail it.

FrankenWashie
02-08-2018, 04:48 AM
Nah, it's a keeper, Celestions are good speakers.

Only kidding Doc😜😁

DrNomis_44
02-08-2018, 09:19 AM
Only kidding Doc😜😁


Yeah I know, it's all good mate.

DrNomis_44
03-08-2018, 08:18 PM
Update:

Did some work on the Super Twin amp chassis this afternoon, this involved replacing the original power and standby switch (they seemed a bit sluggish in operation) with two new 240V AC 3A DPDT Toggle Switches I bought from Jaycar Electronics, while I was in the process of replacing the original standby switch, I noticed that there was a wire and the + terminal of a 100uF/350V cap that was supposed to be soldered to one lug of the switch, in fact, they had not been properly soldered to the lug at all, just crimped onto it, so I made sure I soldered them in place on the new switch.

Going to be doing some more work on the Super Twin amp tomorrow, which will involve replacing the original 240V AC mains lead with a new one.


Stay tuned for more updates......

DrNomis_44
14-08-2018, 12:48 PM
Update:


Had to take a break from working on the Super Twin last week, reason being.....my 48 Watt Temperature-controlled Soldering Station simply wasn't "cutting the mustard" when it came to de-soldering the old mains earth wire from the chassis, realized that I needed a soldering iron with more grunt in it, so today, I went to my local Bunnings shop and bought a new 50/100 watt soldering iron, which proved quite up to the job, moral of the story.....if you're planning on doing servicing work on guitar amps, you need more than one soldering iron, a medium wattage one and a higher wattage one to de-solder those big solder blobs on the chassis, some amp manufacturers use the amp chassis as part of the grounding system, and the chassis can act as a huge heatsink, soaking up all the heat you pour into the solder joint, hence the need for a soldering iron with lots of grunt.


Of course, in hindsight I should have known that......


Stay tuned for more updates.

Marcel
14-08-2018, 03:34 PM
Oh my !!

At last count (from memory) I have at least Five temp controlled irons between 40W and 60w (Hakko & Scope & DSE), Two desoldering/vacuum pump irons at about 60W each, Two 25W tool box irons, A 12W 12VDC iron, Two old style 6VAC 25W Scope transformer irons, a 120W heavy duty iron, and 'the beast' Birko 300W iron with a 1" diameter tip (and 10min warm up time).... I'm sure there are others that I've missed...

I really need to take a family shot of all my soldering irons... One day.... And then there's the Cro's, the army of multimeters, the sig-gen's, and the hand-tool's... Oh so many hand tools... and tool box's and parts box's, and ....

DrNomis_44
14-08-2018, 04:27 PM
Update:


Just a quick update from me, okay so I finished the work on the Super Twin amp, gave the mains wiring a check with my multimeter set to the 20M range, to check that there are no shorts to ground, everything looked good, I checked that there was complete circuit from the Neutral-pin to the Active-pin when the power switch is switched-on, all good there, I then decided to put the chassis back in it's wooden cabinet and give the amp a test-out with the Ashton quad box, after plugging the amp into the quad box I plugged it into a power board that was getting mains power, gingerly I switched the power switch on the amp on, hoping that there wouldn't be any bangs, smoke, screeches, or any other weird, and, or, abnormal behavior, nothing bad happened, the power indicator light lit-up, then I turned on the cooling-fan switch, the two fans whirled into life with no squeaking sounds, they were quiet, since that had all gone well without any mishaps, I switched the standby switch off so that the amp was fully running, still no bangs, smoke, weird, and, or, abnormal behavior.....cool, I turned up the master volume to about three and brought the channel volume up while plucking a string on my Fender Strat, I was greeted by a nice and clear twanging sound through the speakers of the quad box....it's alive!...it's alive!....IT'S ALIVE!!!!


The amp seems to be working perfectly well with the Ashton quad box, I'm getting some really nice clean tones from it, this amp is very powerful sounding, but very dynamic too, pick softly and it is very polite, pick or strum hard and it barks back.


I am very happy with it, it just needs a new front baffle for the wooden case and then it's gig-worthy.

Marcel
14-08-2018, 07:05 PM
Way to go Doc !!!

DrNomis_44
14-08-2018, 07:11 PM
Way to go Doc !!!


Cheers mate, what's really cool about getting my super Twin amp up and running again is that I'm still alive to talk about it.

Marcel
14-08-2018, 09:43 PM
Cheers mate, what's really cool about getting my super Twin amp up and running again is that I'm still alive to talk about it.

You should be looking at it as skill and experience.... and that Luck had nothing to do with it...lol

DrNomis_44
19-08-2018, 01:23 PM
Here's a pic of the Fender Super Twin amp, sitting on top of the Ashton quad box in my loungeroom, the amp has it's new front panel fitted to it's wooden cabinet:

27808



The front panel of the amp's wooden cabinet is just a piece of 12mm X 180mm X 627mm planking I bought from my local Bunnings store, I also bought a can of matt black spray paint and sprayed the piece of wood with it, seems to work pretty well, later on i'm going to cover the front panel with some nice Paisley cloth, should look cool once it's finished, the amp is pretty much useable as is though, but one thing I would like to do later on is re-tolex the wooden cab after stripping-off all the old tolex, and re-gluing the corners, I'm also going to fit new chrome corner protectors and etc to the cabinet.

DrNomis_44
21-08-2018, 01:36 PM
Update:

I'm guessing that some of you out there are probably going to be pretty interested in hearing what my Fender Super Twin amp actually sounds like...right?, well, as it just so happens, I managed to record a quick and dirty little audio demo of the amp, and also managed to upload it to my account at soundcloud, so, without further ado, here's a link to it if you're interested in checkin it out:

https://soundcloud.com/drnomis_44/super-twin-demo

Here's another demo, this time I'm using my Ibanez TS-9 Tube screamer to dirty-up the sound a bit:

https://soundcloud.com/drnomis_44/super-twin-demo-overdrive

FrankenWashie
21-08-2018, 03:35 PM
Pretty crisp Doc. Hows about a little overdrive and distortion!

DrNomis_44
21-08-2018, 03:52 PM
Pretty crisp Doc. Hows about a little overdrive and distortion!


It doesn't really do overdrive and distortion all that well even though it does have a Distortion control, there's hardly any distortion when the distortion control is maxxed out, it's a very clean amp, I guess I could do another demo with either my TS-9 Tube Screamer or BD-2 Blues Driver, it does take pedals really well.

I still have some play-time left on my soundcloud account so I'll record a second demo with an overdrive pedal and add it to the post with the clean demo.....stay tuned.

wazkelly
21-08-2018, 09:16 PM
I reckon the TS-9 will make it sing. Sounds very nice clean.

blinddrew
22-08-2018, 04:42 AM
Sounds good to my ignorant ears. :)

DrNomis_44
22-08-2018, 11:34 AM
Update:

Just posted a link to a second demo just under the one for that first clean demo.

Simon Barden
22-08-2018, 03:26 PM
You can certainly tell your Strat has a RW/RP middle pickup. Sounds good.

DrNomis_44
22-08-2018, 03:50 PM
You can certainly tell your Strat has a RW/RP middle pickup. Sounds good.


Yep, since positions 2 and 4 on the pickup switch are hum-free, I'm in the process of buying a full set of Fender Hot Noiseless pickups on eBay, once they're installed the hum in the other three positions will be gone, as much as I like the stock fat 50's pickups, they're a bit too noisy for me, they are a bit weak in output for my tastes too.

DrNomis_44
31-08-2018, 03:14 PM
Update:

So, I bet you guys are interested in hearing about what I've been up to this week, well, I've been in the process of making a complete new footswitch for my Super Twin amp, yes, it does feature footswitching, the built-in 5-band EQ, Distortion, and Volume-boost are all foot-switchable, I went to my local Jaycar Electronics shop on Tuesday and bought all the bits and pieces needed to make the new footswitch, here's a couple of pics of it:

27920

27921


The new footswitch seems to be working perfectly, with the new footswitch unplugged from the amp, the 5-band EQ, Volume Boost, and Distortion is always on, although you can switch the Distortion on or off with the Distortion control knob, now, when you plug the new footswitch into the sockets on the back panel of the amp, the 5-band EQ-, Volume-boost, and Distortion can all be switched on or off remotely just by stomping on the footswitches, this means you can pre-set the 5-band EQ and Distortion controls to get the sounds you want, and still be able to get the basic clean sound of the amp, the Distortion itself is nothing to write home about though, you can always just use a distortion pedal since the amp does take pedals well.

Sonic Mountain
31-08-2018, 03:44 PM
Happy B'day Doc.

Looks like a neat setup.

DrNomis_44
31-08-2018, 09:26 PM
Happy B'day Doc.

Looks like a neat setup.


Hey cheers mate, yeah I think I've got it all working the best it can, it's good to go with regards to recording or gigging, I can't wait to do my first gig with the amp to break it in.

DrNomis_44
04-09-2018, 04:44 PM
Update:

Some new bits and pieces for my Super Twin amp arrived in the post this afternoon, in the parcel were two new Fender style amp knobs, two new Blue lamp bezels, and a complete new lamp holder which I'm going to use as a spare in case the Super Twin amp's stock one breaks, the two new blue bezels fit the new lamp holder perfectly, I don't know if they'll fit the stock one though, I'll have to wait till tomorrow, I've got one of the new knobs installed and it looks great, it's a bit shinier than the stock ones, but I'm not too worried about that.

Simon Barden
05-09-2018, 06:34 PM
Right at the other end of the Fender power scale...

27966

I've borrowed a friends '81 Fender Vibro Champ. 5W with a 4-Ohm 8" Eminence speaker. One 6V6 power tube, one 12AX7 for the preamp, one 12AX7 tube for the tremolo circuit and a 5Y3GT for the rectifier. The tremolo circuit uses power tube grid bias adjustment to change the volume. The circuitry (AA764) hadn't changed since the Blackface model Vibro Champ was introduced in 1964, though the fitted speaker has changed over the years.

As you might have guessed, with 5W and an 8" speaker, it's not very loud and it hasn't got much clean headroom. With a Strat, it starts to break up with the volume at 4. With a Les Paul (humbuckers and P90s), that point comes at 3. Above 5, it doesn't get louder, just dirtier.

The tone controls aren't that effective. Bass works from 1 to 5, above which nothing else happens. It may well do more, but the fitted speaker can't produce the bass frequencies necessary to hear the effect. Treble works from 5 to 7; below 5, nothing is added and above 7 almost no change can be heard.

The tremolo is quite a nice effect, but it's really wasted IMO as there isn't enough clean volume to make it worthwhile. It hasn't got quite the depth of effect that some tremolo circuits have. It also doesn't sound that good with a driven sound. What would have been more worthwhile would have been a reverb; there's enough space in the cabinet for a short-spring unit. My cheap Tone City Temble pedal does a very good imitation of this amp's tremolo, though the intensity control on the pedal can produce a full 'silence in the gaps' tremolo.

It's main use is really an easily driven small recording combo where it's ideal for crunchy sounds that still retain some clarity. Think raunchy Stones numbers. It sounds dirty, but it hasn't got bags of sustain - it's not going to give you anything like a long creamy lead sound without external help from pedals. It's better with humbuckers or P90s for this as Fender single coils can sound rather thin and scratchy with the drive sounds, as the lack of any real bass makes the single coil sounds rather scratchy. Even humbuckers don't sound overly bassy, but in a mix, that light low end will stop the guitar sound from fighting with the bass guitar.

For a small Fender combo that's got some decent clean headroom and that works well with Fenders, you really need the next step up on the Fender amp hierarchy and move to the 12W Princeton Reverb. This has a 10" speaker, reverb and tremolo.

Am I tempted to make my mate an offer for it? Yes and no. He's now got some Adam A7X monitors from me that he's trying out. If he wants to keep them, then I'll offer to swap those for the amp (he's got a small Blackstar that he finds more useful). But I don't think I'd offer him cash for it.

DrNomis_44
05-09-2018, 09:06 PM
They're not bad, those Fender Vibro Champs, you might be able to upgrade the speaker to a 10 inch one, although you might have to replace the stock front baffle to be able to do so, I've got a Guitar Classics magazine that has an article about upgrading the speaker in a Fender blackface Champ with a 10 inch speaker, so it is do-able, apparently the author of the article reckons the speaker upgrade made the amp sound a lot better.


The Super Twin is sounding pretty good with my pedal board setup, I'm really surprised at how well the amp takes pedals, it's got tonnes of headroom due to the six 6L6 power tubes being connected up in what's called the "Ultra Linear" configuration, this means that the six 6L6 tubes can put out quite a fair bit of power, 180 Watts R.M.S. (R.M.S. is short for Root Mean Squared), and a peak power output of 395 watts, all at low distortion, I don't really need to crank the preamp and master volumes up much, about three for both is loud enough for my loungeroom, having tonnes of headroom means that the sounds I get with the pedals are going to be pretty clear, the bright switch definitely has an audible effect, the amp sounds warm when the bright switch is turned off, but there is still plenty of highs in the tone so it doesn't sound muffled, I've been spending a bit of time familiarizing myself with the amp, getting to know it and how to get good tones out of it, the funny thing is, some Super Twin amp owners say that it's hard to get a good tone, but my experience has been the exact opposite, I've found it really easy to get good tones, I've done some experimenting with the 5-band EQ and you don't have to do much with it to get some good tones with that either.

The amp definitely sounds better with the footswitch plugged in though, I like what the volume-boost footswitch does, but I'm not a big fan of the amp's built-in distortion, fortunately I can easily use a distortion pedal instead, the red JD-F2 Fuzz Face sounds great through the amp, as does my TS-9 Tube Screamer and BD-2 Blues Driver, the other pedals broaden the tonal palette I've got to work with, and I can use them to doctor clean tones if I want.

Simon Barden
05-09-2018, 09:16 PM
Yes, even a better 8" speaker would be a worthwhile upgrade over the awful cheap Eminence that it's got at the moment. At least that wouldn't devalue it if I kept the original. These things are going up in value. It's in good condition (I've cleaned most of the dirt off it since I took the photo) and would probably go for around £600, currently over Aus$1000. It's one with a multi-tap mains transformer and a rear voltage setting switch, so could be used anywhere.

DrNomis_44
05-09-2018, 09:29 PM
Yes, even a better 8" speaker would be a worthwhile upgrade over the awful cheap Eminence that it's got at the moment. At least that wouldn't devalue it if I kept the original. These things are going up in value. It's in good condition (I've cleaned most of the dirt off it since I took the photo) and would probably go for around £600, currently over Aus$1000. It's one with a multi-tap mains transformer and a rear voltage setting switch, so could be used anywhere.


You could consider replacing the stock speaker with something like a Jensen, if you wanted to upgrade to a 10 inch speaker, maybe something like a Jensen C10Q might sound good, I've got one in my Legacy 5 watt amp and it did wonders for the amp, considering that the stock speaker sounded muddy and midrangey.


I'm still very surprised at how well the four Celestion G12E-50 Rocket 50 speakers, in the Ashton quad box, work with the Super Twin amp, it's as if there's a synergistic thing going on, where the speaker's frequency response compliments the frequency response of the amp, Fender amps are known to have a midrange notch in the frequency spectrum, and Celestions do have a bit of midrange in them, so they complement each other nicely, well that's my theory anyway.

DrNomis_44
27-12-2018, 11:58 AM
Update:


The Fender Super Twin is still working great, I had a chance to try my Fender Strat through it after swapping out the stock Fat 50's pickups for a set of Fender N4 Noiseless pickups, still sounds pretty good, but I might need to tweak the hum balance control on the back panel of the Super Twin a bit cause the amp does still have some background hum.

Might post another demo later on.

Marcel
27-12-2018, 12:51 PM
How do the N4's compare to the Fat 50's ??

I have vintage noiseless in my Deluxe Strat. They sure have the clean tone that a Strat should be but by my reckoning they are noticeably lower in output level. I'd be guessing at about 1/4 to 1/3 of what the set of 490R/498T HB put out in my LP, and 2/3 the level of my MIM loaded ply Strat.... Maybe when they (Fender) say 'vintage' they mean underwound compared to today's offerings...

DrNomis_44
27-12-2018, 01:29 PM
How do the N4's compare to the Fat 50's ??

I have vintage noiseless in my Deluxe Strat. They sure have the clean tone that a Strat should be but by my reckoning they are noticeably lower in output level. I'd be guessing at about 1/4 to 1/3 of what the set of 490R/498T HB put out in my LP, and 2/3 the level of my MIM loaded ply Strat.... Maybe when they (Fender) say 'vintage' they mean underwound compared to today's offerings...


Tonewise, the N4s in my Fender Strat are about the same as the Fat 50's, the real difference is that I'm no longer getting that annoying background hum with the N4s, like I did with the Fat 50's, the N4s seem to have a bit more output than the Fat 50's too, but then that might be because I've set the pickup heights so that both the low E and high E pole pieces on each pickup are about 3/32 Inch close to the E strings when they are fretted just behind the last fret.


I'll record a quick demo later on so you can hear what they sound like.


I just remembered trying some Fender Noiseless pickups on my old Mexican Strat that I used to have, I remember them sounding a bit thin and weedy, they might have been the vintage noiseless ones cause their output was a bit low.

I'll record a quick demo now so you can hear what the N4s sound like, I'll be recording directly into my laptop via a Scarlett 2i2 usb audio interface, and I'll be using an amp plugin called Emissary, and a speaker cab simulator plugin called Nadir, in FL Studio.


Here you go, hope this gives you some idea of what they sound like, notice that there's very little background hum noise:

https://soundcloud.com/drnomis_44/amp-plugin-tester-2-n4-pickups-demo-1


Personally I think they're fine, you get that single-coil pickup tone without that annoying background hum noise that you get with conventional single-coil pickups, even though the N4s are technically humbuckers from what I've read.

Marcel
27-12-2018, 03:20 PM
Thin and weedy....lol

I wouldn't say that, but 'a bit low' I would. My MIM Deluxe is still as per factory settings so maybe it's just me needing to adjust my expectations when swapping between it and my LP.

The demo sounds good...

DrNomis_44
27-12-2018, 03:26 PM
Thin and weedy....lol

I wouldn't say that, but 'a bit low' I would. My MIM Deluxe is still as per factory settings so maybe it's just me needing to adjust my expectations when swapping between it and my LP.

The demo sounds good...


Cheers, I reckon it was definitely worth doing the upgrade to the N4s, it means I can record cleaner sounding demos without the hum noise, which used to put me off a bit.

I still have the set of three Fat 50's packed away in a plastic bag.


I also ended up swapping-out the original stock bridge of my Fender USA Strat for a new chrome SuperVee Bladerunner bridge, because the knife edges on the stock bridge had some wear on them, and the stock bridge wasn't returning to neutral like it was supposed to, and then the stock tuners wore out which forced me to install a set of vintage-style Klusons on the headstock.

wazkelly
29-12-2018, 10:10 AM
Sounds very clean Doc.

Sent from my SM-A520F using Tapatalk

DrNomis_44
29-12-2018, 12:35 PM
Sounds very clean Doc.

Sent from my SM-A520F using Tapatalk

Yep, no more annoying background humming in all the pickup-switch positions, I can use higher gain settings on my Marshall amp, and my TS-9 and Blues Driver pedals.

DrNomis_44
12-03-2019, 09:50 AM
Been playing my recently acquired Mexican Tele through my Super Twin amp and found that if I added either my TS-808 Tube Screamer, or my TS-9 Tube Screamer to the mix, I've got a serious tone machine on my hands, especially with the Mexican Tele's neck pickup, I think I've discovered the perfect rig for playing Blues, Fender Super Twin, TS-808, or TS-9, and a good Fender Tele, I'll have to record a demo for you guys this weekend if it's not too noisy outside, I'd do it today but there's some guy doing some lawn mowing outside.

It's funny how Fender guitars and amps seem to just work together well, well of course, both are made by the same company, did you know that Leo Fender (his full name is Clarence Leonidas Fender) wasn't actually a musician himself, he was a radio repairman, but he got all the original designs right first time.

dave.king1
11-04-2019, 03:45 PM
Here ya go Doc, a Super Twin in action


https://youtu.be/PQ5UlyBgHN8

DrNomis_44
12-04-2019, 02:49 PM
Here ya go Doc, a Super Twin in action


https://youtu.be/PQ5UlyBgHN8


Cheers mate, never heard of them before but cool song, I wonder if that Super Twin the guitarist is playing through is the same model as the one I have, cause there's two different models of the Super Twin that Fender made, although the front panel looks the same, there's the one that has a tube driven spring reverb circuit, and the one that doesn't have it, mine is the one without the reverb circuit.

Andy123
13-04-2019, 01:07 PM
Here ya go Doc, a Super Twin in action


https://youtu.be/PQ5UlyBgHN8

That's quite a nuanced precision performance from the keyboard player ;)

DrNomis_44
06-06-2020, 11:03 AM
Update:

Going to be modding the footswitch for my Fender Super Twin amp today, so that it has three indicator Leds on it, this way I can tell at a glance when the EQ, Volume Boost, and Distortion circuits are activated or not.

jugglindan
06-06-2020, 06:08 PM
Sounds cool. I love indicator lights on everything. Pedal boards should look like a starship console IMO.

Also, for some reason I thought this forum was just for the Pitbull amp kits (whatever happened to that idea?), but looking back I see this is where people put their own amp builds and projects too. Makes sense. I should have put my Noisy Cricket project here instead of the DIY pedals forum (although I feel a bit embarrassed putting my dinky little amp alongside things like Andy's 5e3 build).

Simon Barden
06-06-2020, 06:24 PM
The PBG 5W champ-style amp came and went some time ago now, so this seems to be the place for amp builds or mods.

DrNomis_44
06-06-2020, 06:48 PM
I'm happy to report that the indicator leds mod I did to my Super Twin amp's footswitch pedal, appears to be working as it's supposed to, now, instead of having to guess whether the EQ, Volume Boost, and Distortion are on or not, all I have to do is look at the leds on the footswitch and they tell me all I need to know.

I may need to change a resistor out to tame the brightness of the blue indicator led I used for the Volume Boost function though, that'll be a job for tomorrow, but for the time being, I'm happy with it.

I used a spare +4.8V DC/700mA plugpack adaptor as a power supply for the leds, and used the spare poles of the three 3PDT footswitches to switch the leds on when the EQ, Volume Boost, and Distortion are switched-on, the distortion isn't all that usable though.

jugglindan
06-06-2020, 06:53 PM
All the blue LEDs I have are powerfully bright. I swapped the CLR twice in the buffer before it stopped blinding me.

DrNomis_44
06-06-2020, 07:10 PM
I did a quick calculation to determine what value resistor I needed to use to limit the current flowing in each led, standard 3 or 5 mm leds can safely run with a maximum of about 20mA flowing through them, any higher than that and you risk destroying the led, and they can actually explode if there's too much current flowing through them, so I deliberately chose to limit the current to about 10mA for each led, the value of the current limiting resistors worked-out to be 330 Ohms, I used three 330 Ohm 1W Metal Film resistors, and they seem to do the job fine, but I'm definitely going to swap the blue led's 330 Ohm current limiting resistor for a higher-value one to tame the brightness, but that's a job for tomorrow.

When a led explodes, it gives-off a very pungent smell, how do I know?, I've had first-hand experience with it.


As a side-note, my pedal board is all up and running again, ready for gigging or recording.

McCreed
06-06-2020, 07:40 PM
Totally off topic, but...

First, I didn't know anyone (else) in Australia knew who NRBQ are, and second, I met those guys on the ferry to Martha's Vineyard (Massachusetts, USA) around 1996 or so. The band I was playing in was headed to the island for a gig and so was NRBQ.
Joey Spampinato and Terry Adams had filthy hangovers and the ferry ride was pretty rough. Despite feeling like crap, they hung out and chatted just the same.
I nearly forgot about that. Thanks for the memory, and sorry for the hijack!

jugglindan
06-06-2020, 09:04 PM
I did a quick calculation to determine what value resistor I needed to use to limit the current flowing in each led, standard 3 or 5 mm leds can safely run with a maximum of about 20mA flowing through them, any higher than that and you risk destroying the led, and they can actually explode if there's too much current flowing through them, so I deliberately chose to limit the current to about 10mA for each led, the value of the current limiting resistors worked-out to be 330 Ohms, I used three 330 Ohm 1W Metal Film resistors, and they seem to do the job fine, but I'm definitely going to swap the blue led's 330 Ohm current limiting resistor for a higher-value one to tame the brightness, but that's a job for tomorrow.

When a led explodes, it gives-off a very pungent smell, how do I know?, I've had first-hand experience with it.


As a side-note, my pedal board is all up and running again, ready for gigging or recording.

I think I ended up using 2.4k for the blue LED in the buffer. I normally just put the LED in a breadboard and try resistor values until the brightness looks about right. This is only around 2 or 3mA running off 9v but the brightness looked good.

DrNomis_44
06-06-2020, 10:23 PM
I think I ended up using 2.4k for the blue LED in the buffer. I normally just put the LED in a breadboard and try resistor values until the brightness looks about right. This is only around 2 or 3mA running off 9v but the brightness looked good.

I've used a resistor value as high as 47k for a blue led running on a +15V DC supply, and it was still pretty bright,I did a quick calculation and found that a 3k3 resistor will limit the current to 1mA on a +4.8V DC supply for a Blue led, I used 1.5V for the forward-voltage of a Led in my calculation.


I used the following formula to calculate the resistor value:



R=Vs-Vf/I


R= Resistance.

Vs= Supply Voltage.

Vf= Forward-biased Voltage of the Led (typically about 1.5V for standard 3mm and 5mm Leds).

I= Led Forward-Biased Current.


Although, some 3mm and 5mm Blue leds have a Forward-Biased Voltage as high as 3V.

jugglindan
07-06-2020, 06:23 AM
Same Ohm's law calculation that I use. I measure each LED with a DMM to get the forward voltage, since mine are quite variable. I measured my last blue LED at Vf=2.5, and my red at 1.8. So that gives me 2.7mA with the 2k4 CLR. Not much current but it still feels bright.

I like having a low current draw because I use a common power supply that is only rated to 2A. Although that's an awful lot of analog pedals needed to max it out, the digital pedals I have draw a couple of hundred mA rather than the 40 to 50 mA of the analog pedals. I find it hard to believe some of the numbers in The Power List (http://stinkfoot.se/power-list). For example, they claim a TS-808 draws just 7.5mA. Even with a high CLR, just the indicator LED is half of that total.

Edit: I should make a modified power cable so I can measure current draw directly, just to satisfy my curiosity. I am particularly interested in the differences between bypassed and active.

DrNomis_44
07-06-2020, 09:42 AM
Update:


I have just swapped-out the blue led's 330 Ohm current-limiting resistor for a 3k3, doing that seems to have done the trick with regards to taming the brightness so I'm happy with it now.


Here's a pic of the modded Super Twin footswitch pedal, with all three indicator leds working:

35551


If the EQ is switched-on, the green led lights.

If the Volume Boost is switched-on, the blue led lights.

If the Distortion is switched-on, the red led lights.


You can switch on or off any combination of the three functions.

Andy40
11-06-2020, 03:53 AM
Very cool doc

DrNomis_44
11-06-2020, 09:26 AM
Very cool doc


Cheers mate, not only is it cool, it's also very practical as well and saves a lot of headaches, I always like coming-up with practical solutions to problems, and sometimes the simplest solutions can often be the most effective ones.

JohnH
12-06-2020, 05:32 AM
Good work doc

DrNomis_44
12-06-2020, 12:37 PM
I'm going to be heading out to a mate's place to do some demo recording in his home studio this afternoon, I'm going to be taking my Fender Super Twin amp, plus my pedal board, three guitars and a bass, and some other bits of gear with me, my mate has a Quad Box I can use with the Super Twin, should be lots of fun.

Andy40
13-06-2020, 03:37 AM
Jealous. Have fun

DrNomis_44
13-06-2020, 04:19 PM
Jealous. Have fun


I just got back home this afternoon, we had a great time and managed to record a couple of rough-jams, my mate played drums, but since his kick-drum pedal wasn't working he had to make-do without a kick-drum, the Super Twin sounded great through his Quad Box, and the footswitch functioned flawlessly, my pedal board sounded great too, I'm getting a pretty good range of sounds out of it, I might need to do some maintenance-work on my Univibe pedal since it was a bit temperamental when first powered-up, not sure what the cause might be, the dual-gang pot in the speed controller foot-pedal might need a spray with some electrical clean and lube to sort it out.

DrNomis_44
26-08-2020, 04:20 PM
Just doing some minor servicing-work on my Fender Super Twin amp at the moment, one of the input sockets seems to go a bit intermittent every now and then, also one of the octal sockets for one of the six 6L6 power tubes seems to have some contacts that need re-tensioning.


So, here's what I'm going to do:


1 Replace both of the stock input sockets with a couple of new ones.

2 Replace all the Carbon Comp input resistors ( 2 X 33k and 1X 1M) with some new 1W Metal Film resistors, mostly cause I've got them, secondly, Carbon Comp resistors are notorious for generating lots of hiss-noise, secondly they go high in value over time.

3 Re-tension all the contacts in all the octal-sockets of all six 6L6 power tubes.

4 Spray all the control pots and bright switch with some Electrical Clean and Lube.


Hopefully after all that it should be all good.

Update:

After studying the schematic for my Super Twin amp, it appears that when you plug into input one, the signal goes through one 33k grid resistor, if you plug into input two the same thing happens, the signal still goes through one 33k grid resistor, what I believe should happen is this.


Plug into input 1, the signal should pass through one 33k grid resistor.

Plug into input 2, the signal should then pass through the two 33k grid resistors connected in parallel with each other.

Or am I mis-understanding it?, I don't really understand why Fender would design the input wiring so that no matter which input you plug into, the result is always the same, why have two inputs then?

My understanding is that the two inputs are supposed to give two different levels of gain, or, to attenuate the signal level coming from a pickup with a hot output, such as a humbucking pickup.

JimC
26-08-2020, 06:40 PM
why have two inputs then?
Back in the day, at amateur level, more than one instrument per amp was fairly normal.

DrNomis_44
26-08-2020, 07:03 PM
Back in the day, at amateur level, more than one instrument per amp was fairly normal.


Ah rightio, that makes more sense then, I'm going to mod the inputs so that you can get different gain-levels like you do with Marshall amps.

Dacious
26-08-2020, 07:17 PM
It weighed 45kg as a combo. They came on casters.

If it's old check out the filter capacitors - if they're leaking goop it's imperative to change them. If one lets go they're messy and the electrolyte is sticky and corrosive. If it shorts it can take expensive bits with it. They were around from 76-82.

Decent master volume. The distortion is a love it or leave it.

This is the non-reverb version?

DrNomis_44
26-08-2020, 07:34 PM
It weighed 45kg as a combo. They came on casters.

If it's old check out the filter capacitors - if they're leaking goop it's imperative to change them. If one lets go they're messy and the electrolyte is sticky and corrosive. If it shorts it can take expensive bits with it. They were around from 76-82.

Decent master volume. The distortion is a love it or leave it.

This is the non-reverb version?


Yep, it's a non-reverb Super Twin, it still has the foot switchable 5-band EQ, and built-in distortion that I don't really care for, I'm going to have a look under the doghouse cap-cover to see what condition the main supply filter-caps are in.


The two original input sockets were a bit worn-out and definitely needed replacing.


Update:


I had a look under the doghouse/main filter-cap cover, and spotted a 16uF/500V electrolytic cap that looked like it had leaked some dark looking goo, so, until I can order a complete set of new caps for the Super Twin, it's going to remain on my makeshift workbench, the input jack replacement seems to have gone well though.


If I'm going to replace that 16uF/500V electrolytic cap that leaked, I may as well cut-to-the-chase and do a complete cap-job on it.

Simon Barden
26-08-2020, 10:29 PM
Indeed. The ESR of almost all of the electrolytic caps (if original) is almost certainly a lot higher than it should be and even though there might be no obvious leakage from the caps, most are probably well past it.

Most two input amps had one that was a lower sensitivity than the other. No idea why, as the lower sensitivity input generally sounded rubbish compared to the standard input. I think the input impedance was generally lower so as well as less volume you got less treble (at least with a passive guitar plugged straight in).

DrNomis_44
26-08-2020, 11:00 PM
I seem to remember reading somewhere that electrolytic caps are reckoned to have a working-life of at least ten years or so before they go faulty, well at least those vintage caps anyway, I had been noticing that the amp did hum a bit, just a slight amount of background hum, so I'm guessing that the 16uF/500V cap I spotted that had some dark coloured goo leaking out of it, is probably the culprit, tube circuitry operates at high impedances, so if a supply filter cap goes high in ESR that affects it's ability to filter-out mains hum by bypassing it to ground, remembering that caps block DC and pass AC as part of their operation, when a cap goes high in ESR, it effectively looks like it has a resistor in series with it, and it's ability to pass AC is reduced.

That's not the only way a cap goes faulty, I've seen/heard at least one electrolytic cap literally explode, another way a cap goes faulty is if it develops a short-circuit, or partial short-circuit between it's plates, in a tube amp, a shorted, or partially shorted cap can damage more expensive parts, like the power and output transformers, a partially-shorted, or leaky cap can cause something called Red-Plating in power tubes, where the plates or anodes start to glow red due to too much current flow, the plates/anodes can literally melt if there is way too much current flowing in the tube.

Normally, when an electrolytic cap is brand-new, it's ESR is low, but when the cap's electrolyte dries out, the ESR goes sky-high, this is usually caused by a rupture in the rubber bung that seals the positive end of the electrolytic cap (RT style cap).


For those of you unfamiliar with the term ESR, it is short for Equivalent Series Resistance.

McCreed
27-08-2020, 06:24 AM
Re: 2 inputs

I'm no authority on this, but my understanding has always been that it is a carry-over from the 50's (particularly the Fender Tweeds). The inputs were labelled "INST" and "MIC".

The "MIC" input had/has a -6db pad to allow a Hi-z microphone to be plugged in without feeding back. So the amp could be used essentially as a vocal PA and an instrument amp. Over time, manufactures just dropped the "mic" label but kept the input padded.

At least that's what I told many years ago.

Simon Barden
27-08-2020, 09:20 AM
But the Inst and Mic inputs had their own gain controls, at least on amps like the tweed Deluxe, so were really two-channel amps with a common basic EQ as opposed to two inputs for one channel.

The two inputs with different sensitivities on a channel would probably have been to accommodate single coils and humbuckers/P90s from the times when the guitar sound was supposed to be as clean as possible, before overdriven sounds were embraced and desireable.

DrNomis_44
27-08-2020, 01:59 PM
I just checked the Evatco website and they stock a big range of electrolytic caps, I really want to go with all F&T caps as replacements, but some values, like 200uF/500V, I need are currently listed as on "back order", so it looks like I need to wait.

Simon Barden
27-08-2020, 02:16 PM
Tried other suppliers for F&T caps? I know it’s nice to try and get all your parts in one go to minimise shipping, but if it’s holding your project up, it’s worth looking around.

DrNomis_44
27-08-2020, 02:57 PM
Good point, I can't really do any ordering cause I'm broke so I'll have to wait till I can afford the new caps.

Simon Barden
27-08-2020, 03:05 PM
Then there's always that. ;)

Dacious
27-08-2020, 10:19 PM
F&T are okay caps - there's nothing wrong with Vishay. Sprague the brandname is owned by Vishay - if you cut the new big blue Spragues that llook good for restos apart, you find a small Vishay cap inside. Due to improvements in cap materials modern high voltage caps are small.

The 6X8 is readily available pretty cheap NOS or used. The 6C10 on the other hand, is not readily available. My 83 Superchamp uses it. Last time I bought them, I got a couple of second hand ones for about $85. One is a Du Pont and the other is a GE. 6AC10s fit OK, but the envelope is a bit bigger, and it has a 100% and two 70% gain triodes. That is a 12AX7, with the second two are equal to a 12AT7 set of triodes.

A lot of people convert the compactron socket. It can take a 9 pin and a 7 pin side by side in the same opening. A 6AU6 is a single triode of 100% gain - i.e. it's half a 12AX7 triode. 6AU6s are very plentiful and it's a tiny tube. One of the guys on the tele board made an adaptor that plugs into the compactron 10-pin and fits two 12AX7s giving you a spare triode.

DrNomis_44
14-09-2020, 03:57 PM
F&T are okay caps - there's nothing wrong with Vishay. Sprague the brandname is owned by Vishay - if you cut the new big blue Spragues that llook good for restos apart, you find a small Vishay cap inside. Due to improvements in cap materials modern high voltage caps are small.

The 6X8 is readily available pretty cheap NOS or used. The 6C10 on the other hand, is not readily available. My 83 Superchamp uses it. Last time I bought them, I got a couple of second hand ones for about $85. One is a Du Pont and the other is a GE. 6AC10s fit OK, but the envelope is a bit bigger, and it has a 100% and two 70% gain triodes. That is a 12AX7, with the second two are equal to a 12AT7 set of triodes.

A lot of people convert the compactron socket. It can take a 9 pin and a 7 pin side by side in the same opening. A 6AU6 is a single triode of 100% gain - i.e. it's half a 12AX7 triode. 6AU6s are very plentiful and it's a tiny tube. One of the guys on the tele board made an adaptor that plugs into the compactron 10-pin and fits two 12AX7s giving you a spare triode.



Tubes used in my Non-Reverb Fender Super Twin are as follows:


X6 6L6 Beam-Power Tetrodes (actually Mesa/Boogie brand STR 415 6L6).

X1 12AU7 Twin Triode.

X1 12AT7 Twin Triode.

X1 12AX7 Twin Triode.

X2 7025 Twin Triode (low-noise 12AX7/ECC83).

DrNomis_44
18-11-2020, 05:12 PM
Update:

Recently I got in contact with a mate of mine who just happens to do amp servicing, he offered to give me some second-hand 16uF/450V and 22uF/500V capacitors he had pulled out of an amp, but were still perfectly good, so I took him up on the offer, he dropped-off the caps in my mailbox a few weeks ago, and I had a look through them and selected a light-grey 22uF/500V Illinois Cap as a suitable replacement for the 16uF/500V cap that had leaked, I soldered it into place on the eyelet board under the doghouse, then put the Super Twin amp back together and gave it a test-out, the amp seems to be working fine with the replacement cap installed, so that'll do fine till I can get a full set of brand-new caps ordered.


A pic of the old and leaky cap:

38039


Notice how there's an obvious bulge next to the cap's + terminal?, basically what happened to cause that was that, for some reason, the electrolyte inside the cap got hot enough to boil, and because the pressure inside the cap got a bit too much the rubber bung sealing the + end of the cap ruptured, letting the electrolyte leak-out, if you see an electrolytic cap with a slight small bulge in it's rubber sealing bung, or in a similar condition to the one in the pic, it needs replacing with a new one asap otherwise it could cause expensive damage to your amp.

DrNomis_44
04-02-2023, 02:51 PM
Update:


Looks like I'm going to have to do some more service work on my Super Twin amp sometime next week, reason being is that the amp is really noisy sounding, I can hear some loud crackling noises when I take the amp off standby and turn up both of the volume controls, I tried swapping-out V1, the first 12AX7 Tube in the preamp but it didn't fix the crackly noise, although I did notice that the noise went-away the first time I put the 12AX7 tube I was using as a substitute, I discovered that the absence of crackly noise was due to the substitute 12AX7 not being seated properly in it's socket, but that's actually a very useful clue for pinpointing the cause of the crackly noise, I'll need to look at the schematic for my Super Twin amp.


Just had a quick look at the schematic for my Fender Super Twin amp, and I think I know what's causing the crackly noise, I think the treble tone control pot may either be dirty, or it could need replacing with a new one, I'm going to try spraying all the pots in the amp with some electrical clean and lube spray I recently bought from Jaycar Electronics, if that doesn't fix the crackly noise I may have to order some new replacement pots, I think Evatco may have them in stock.

DrNomis_44
09-02-2023, 01:58 PM
Update:

Just did an online order on my account at the Evatco website for two 300pF/500V silver mica caps, there are two 330pF caps in the circuitry associated with V1 in the preamp stage of my Fender Super Twin, one goes from the anode of the first 12AX7 triode gain-stage to ground, the other one connects to one of the lugs on the treble control pot, Evatco didn't have any 330pF/500V silver mica caps in stock, so I decided to go with a couple of 300pF/500V silver micas instead, 30pF is such a small capacitance value that I don't think will make much of a difference to the sound of the amp, considering that the silver micas I ordered have a tolerance of +/- 5% of the marked value, besides, electronic circuits aren't as critical as people might think, you can quite easily substitute the next value up or down with no ill effects.

Taking into account it's tolerance, a 300pF/500V 5% silver mica cap can have an actual measured value ranging anywhere from 285pF to 315pF.

DrNomis_44
15-02-2023, 02:21 PM
Update:

Just got back home from picking-up a parcel from my local Australia Post Office, the parcel contains the two 300pF/500V 5% Silver Mica caps i ordered from Evatco, these will be used as replacements for the two original 330pF ceramic caps in the circuitry associated with V1 in the schematic for my Fender Super Twin amp, incidentally, I replaced five carbon comp resistors in my Super Twin amp with some modern 1W 5% Carbon Film types and that seems to have fixed the loud crackly noise I was getting from the amp before, so, most likely either one of the original resistors, or all of them had gone noisy, I did notice that one of them, a 47k/1W 10% carbon comp resistor had drifted out of spec/tolerance, it actually measured about 53k, a 47k/10% carbon comp resistor in a worst-case scenario should measure about 51,700 Ohms on the high side (47,000+10%=51,700) and about 42,300 Ohms (47,000-10%=42,300) on the low side.

DrNomis_44
19-04-2023, 10:41 PM
Update:

I just ordered a couple new stereo Cliff jacks for my Super Twin amp along with some other things from Evatco.

Update 2:

Just did a quick calculation to see how much 6.3V AC heater current the two power valves and the five 12AX7 preamp valves are going to draw from the new power transformer, and it's going to be a total of about 4.5A, so this power transformer looks to be the most suitable one for the job:

https://www.evatco.com.au/374bx-power-transformer

The HT secondary voltage is a bit higher than specified in the SLOCLONE schematics I'm working with, it specifies a transformer with a 360-0-50-360 V HT secondary at 200mA DC, and the new power transformer I have selected has a 375-0-50-375V secondary at 201mA, it does have two 6.3V AC CT/6A heater secondaries, and one 5V AC CT/3A Rectifier heater secondary, so I reckon it's perfect for the job, the original power transformer I made doesn't have a 50V AC bias tap, so the fact that the new one does have one is a bonus.

DrNomis_44
20-04-2023, 10:40 AM
Here's another question for you, Marcel, in the SLOCLONE schematics I'm working with, the Clean/OD channel-switching is done using opto-isolators that consist of a Led and an LDR, or Light dependent Resistor, a mate of mine who used to do amp servicing told me that those Led/LDR opto-isolators tend not to be very reliable when used in channel-switching amps because they "get the daylights flogged out of them", so, I was thinking of using some 5V relays to do the channel-switching instead of using Led/LDR opto-isolators, that should be quite doable, shouldn't it? I think my Marshall MA100C amp uses relays for it's channel-switching, I'll just need to come-up with a relatively simple to build relay driver circuit that can run on 5V.

DrNomis_44
23-04-2023, 03:28 PM
Update:

Here's a pic of the wooden cab for my mid-70's non-reverb Fender Super Twin amp, I've currently got it on my makeshift workbench in my little studio room in my flat, so I can do some work on it, I have decided to go-ahead and re-tolex it because the old tolex is looking a bit tatty in a few places, this has also given me an excuse to re-glue all the cabinet joinery with some titebond glue because they are a bit loose and rickety, I'm going to be paying my local Bunnings store a visit next fortnight to buy a few things I need, some titebond glue will be added to my shopping list.

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DrNomis_44
09-05-2023, 03:03 PM
Update:

Recently I bought a brand-new Fender amp badge on eBay, and it turned up in the post yesterday, here's a pic I took after installing the new amp badge on the amp's new front baffle I made today:

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