still troubleshooting the 120 hz hum in the output circuit,
found a slightly different schematic from a Randall 100ES,
mainly the resistor to the base of the 2nd diff transistor thru the cap to ground (circled in red)
this RG80 amp has a 330 ohm
the 100ES has a 4.7Km don't know if changing 330 to 4.7 k will improve hum, will give it a try,
resistors that do the most as far as setting up the operating point are the 1K and 1.5K circled in green, they determine current flow down the string that sets up base voltage/current of the tree transistors m
the 250 ohm pot//47 ohm resistor simply vary the current to trim to bias the drivers, output transistors are cut off til a good signal comes thru, drivers run warm til a signal comes thru and gets them to conduct better, the thermistor regulates the heat of the drivers by increasing R and thus reducing current thru the bias string,
that follow, changing the 100 ohm emitter resistors to different values does not do much as most of the current simply flows thru the e-b junction of the next transistor,
changing the 680 ohm resistor to the diff pair does not do much as the tip32 is jammed into saturation unless the 680 is reduced to a much
do not know the purpose of the 22 ohm across D8 o the RG80, it is not used in the 100ES
so the most important resistors in the whole output stage are the R47 and R48 1 watt resistors (RG80)
here is the newer schematic, uses MJ15015 driver and outputs but has the same TIP 31 and 32 amps,
OT: Don Randall worked with Leo Fender way back when,