After checking the various 'regular' Twin schematics on Schematic Heaven, I realized that the first stage of the Super Twin is very close to a standard Twin. However, after that first tube, the Super Twin sends the whole signal to the EQ and Distortion circuits. I thought that if I bypassed all this circuitry I could get a good sound out of the amp.
I looked real hard at the Treble/Mid/Bass eq section and the plate and cathode values of V1 and decided that no changes were needed (other than removing the 'extra' 330pf cap).
The negative feedback circuit is perhaps, better than that they used on the 135w Twins. In those, it looks like the master volume also controls the amount of negative feedback. In the Super Twin design, there is a footswitch to alter the negative feedback (called 'Volume Boost'). I think this is a good design and have kept it in the circuit. There is also the possibility to convert this to a Dumble-style presence control if needed.
Here is the schematic with the mods. Totally reversible, and non-destructive. Sounds killer!! mp3s to follow.
In case you are not familiar with the Super Twin Reverb, realize that it is NOT a Twin Reverb, and it is NOT a Super Reverb. It has six 6L6s in the output section (rated by Fender as 180w). The keys to its poor performance, I believe, are the way the footswitches are used to control the reverb, eq, and distortion. There are no relays, and the footswitches don't totally disconnect the various circuits from the main signal path. The distortion's on-off circuit uses a very clever (to an EE
) voltage dividing circuit so that a simple grounding switch turns on-and-off the cathode of the 'distortion' tube. It avoids a relay, but it sounds like crap.Here is a link: http://www.ampwares.com/ffg/super_twin_reverb.html