I could be wrong but I think the trademark sound of the amp is from the overloading of the transformers.
One of the standard mystifications spreaded around the use of audio-transformers, but not really true.
To "transform" a (huge amount) of AC-voltage you need an iron- or Ferrite-core. The lower the frequency, the bigger the core most be.
For this reason (old) submarines didn´t use 50 Hz or 60Hz, they used 5kHz to reduce the weight caused by the necessary iron.
If the iron is not enough and can´t handle the current it will be "saturated".
So the hypothesis of overloading the transformers maybe true for low-frequencies like bass, but not for normal guitar-frequencies, where the iron is enough not to get saturated....
Yes, you are correct; a pair of 2SB56 are used for the output.
No feedback from the output though - I'm sure of that.
Very, very close to Vanessa's schematic.
But there should also be a small disc (NTC) or diode near on of the output trannies for temperature compensation (not shown in vanessas schematic)
I really love AC128s, but almost all the ones I've gotten lately have been crap... low gains - around 30 to 50 hFE...
Where is the problem ? AC 128 have been (only) constructed for the pupose of power-output stages like this. And there you don´need more hfe. FuzzFace etc is not a typical application for this transistor, it´s a misuse....
Is there any substantial difference between these transformers and the crappy little "42TMxxx" Xicon ones Mouser sells...
No.... these transformers were made exactly for this application, you only have to choose the right one for the desired outputpower and transistors used.
analogguru
There´s a sucker born every minute - and too many of them end up in the bootweak pedal biz.