Fender Super Twin.

[DrNomis_44]

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]

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]

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]

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]

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]

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]

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]

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]

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]

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: