we rewound the Reverb XFMR just to make sure this thing stays working,
good thing as the CBS 022921 has a collapsed core tube and cheap wire,
5200 / 99 turns on a 21 EI, short stack,
when the transformer was installed, amp tone seemed off,
had to investigate, all voltages checked good, hmmm.
why would the reverb xfmr change tone even with the reverb knob turned down?
had to redraw master vol circuit, too hard to understand the Fender CAD jockeys,
after the redraw we found that phase is important,
MV circuit uses neg feedback with switch in, no feedback with switch out,
MVS=Master Vol Sw, two sections, one changes tone, one inserts neg feedback,
normally reverb xfmr phase does not matter as the springs mix everything up and delay signal anyway, but with this amp, you have to get the polarity right,
tomorrow we will flip the xfmr leads and hope that it fixes the tone,
this will change the positive feedback into negative feedback,
as it is, there is very little difference with the MV switch in or out,
interesting circuit, never seen it before,
here is the MV circuit redraw>