Fender Super Twin.

[wazkelly]

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]

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]

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]

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]

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]

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]

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]

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]

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]

Good news on the camera front, Doc.