Sears Silvertone Solid State 100 guitar amp troubleshooting

[freegan72]

I have been troubleshooting my Sears Silvertone Solid State 100 guitar amp, model 1464.  Schematic is here: https://imgur.com/a/15npj

It has this low-frequency hum that sucks most of the power.  Otherwise, the input controls, reverb, tremolo work.  I removed the big PS filter caps (C26, C27), disconnected everything from the bridge rectifier out, and used a lab DC power supply for the +26 V and -26 V. I started lifting components to remove different parts of the circuit (reverb, tremolo, channel 2, channel 1, in that order).  Nothing changed.  I replaced all the e-caps (many of which were bulging and/or a little burnt-looking).  That just made the hum brighter and more powerful-sounding.

If I disconnect everything before Q5 (removing Q4), the hum goes away.  I can plug a guitar into the base of Q5, and it sounds great, super loud.  I checked continuity on the leads of Q3 and Q4, nothing is shorted.  They are marked 67467296.  Any suggestions on replacements?  Anything else I should consider?

Thanks!

[shooter]

I'm just glancing at this because my puter is slow n your page wasn't loading, n it's early!

https://el34world.com/charts/Schematics/files/Silvertone/Silvertone_1423.pdf

is the power stable now with new caps?
without a scope it's kinda hard doing signal path, but a meter should get ALL DCvolts where they should be.

hum is typically bad grounds, bad filtering, bad coupling caps.
you can usually isolate to a stage once DCV is correct by using a listening amp.  Inject a signal in, sample with test amp after each transistor stage.

unknown spec on a transistor can be "guessed" by what's the DC it's operating at, ballpark calculate the Ic using the collector and emitter resistors and DC volts across them.
example Rc = 1000 ohms, Re = 100 ohms vdc 16   so Ic ~~~ 16/1100

[PRR]

> low-frequency hum

Power line pitch? Or something else??