My Version 4 - continuing mods to brighten the tone of this amp. Previously an Emi Screaming Eagle improved tone and helped somewhat with needed brightness. To compensate for the speaker, the power tube bypass cap was increased from 25 to 47uF to recapture bass response. New Mods:
1. Ch 1 retains a simple "guitar-style" one knob, treble-cut tone control. The tone cap was reduced by trial and error sound testing from .003uF way down to 470pF!!! This really brought Ch 1 to life.
I considered trying a Big Muff tone circuit; I'm intrigued by the one knob, mid-cut circuit. But the simple treble-cut now sounds good; and gets bright enough (I think). Also it meets my goal of keeping Ch1 close to the stock 1482 circuit and topology.
2. Ch 2 was further "Fenderized" by lowering the stock plate resistor from 330K down to 100K. This increased the plate voltage from +108 to +210VDC. The tone stack had already been converted to 5F2A specs, but remained too dark. The caps were reduced from Fender spec to 300pF / .003uF. Now Ch 2 seems to be bright enough and has more headroom.
3. Finally got around to installing shorting jacks for the inputs. And, all other plate resistors were replaced with stock values. The amp is pretty quiet now.
All in all I'm happy with the results; and it's still great for slide guitar.
EDIT: schematic revised with minor corrections. Note correct power tube bypass cap value.
* Note there is a modified schematic also posted by Platefire.