So, today, I did the mods that the customer was asking for. The value and
type of a coupling cap in the overdrive channel was changed. The input
circuitry was stripped and simplified to standard Fender style - i.e. a 68k
series resistor from input jack to the grid of the first 12AX7, and a 1M
grid return to deck. The fixed negative bias to the grids of the output
tubes was disconnected, and the injection point decked, and the cathodes
were lifted from deck and returned instead via a 100 ohm 4 watt resistor,
bypassed by 100uF.

I also put an additional 1 ohm resistor in the cathode path, so that I was
able to measure the idle current of the output stage. This settled at about
130mA, or just over 30mA per tube, which was exactly what the author of the
mod notes suggested it should be.

I have to say that after carrying out these mods, the amp did seem to have a
much 'smoother' more Fender-like sound, and was still capable of producing
pretty much its full normal output of around 30 watts. I do not have a
sufficiently 'musical' ear to know if the revised sound is what the owner is
looking for, but it did seem to have a very sweet sound, to me. He is
picking it up tomorrow morning, so I guess I should know if he's happy with
it, in fairly short order ...

Arfa