hartke gt-60 amp hums...

[EDWARDEFFECT1]

hartke gt60.zip amp schematic.

[J M Fahey]

Thanks for posting.
On this schematic I do not see any special reason for the clean channel to hum more than the dirty one, specially since they share the input stage, the most critical one, so the only reason that remains (I do believe what you say) is probably a layout problem, which unfortunately none of us can correct, it's the PCB layout.
A probable cause is that both channels, no matter what they do, *must* converge into U3, a 4053 3 x SPDT switcher, travelling from end to end in that board following not the shortest, best path but the one allowed by the labyrinth of parts and tracks.
The clean channel path obviously goes through some noisy area where it picks up hum.
Grounding signal along itspath may show us where that happens, but you can't rearrange PCB tracks.
Sorry.
And thanks again for posting.
PS: the basic structure reminds of Valvestates.

[EDWARDEFFECT1]

hi jm
just found somethings i overlooked.c-46 has a 5k resistor in it.r-54 has a green film cap in it and r40 reads 0.00 in all ranges of my multimeter. i checked it in both dirrections.guess i'll have to take it out of circuit and see what it reads.do you think i should change c-46 and r-54 to the proper components and values as listed on the print?maybe i'll get rid of the hum out of this beast yet. i'm not sure if these mods were done at the factory or by an individual.the amp works fine in all regards the way it is except for the humm.any ideas anyone!!!!......ed!

[J M Fahey]

I repeat it, I don't think it's a *parts* problem but a *layout* problem.
Just to check what is the "injection point"follow the clean channel backwards, killing stage by stage (so both hum and signal disappear) until in one of them signal dissappears but hum does keep the same, that's the culprit stage.
*Then* you will have to look around it to find what (bad) happens.
Changing parts at random will solve nothing at all.

[EDWARDEFFECT1]

i changed c-46 from a resistor to a 223j capacitor,c-54 from a 223cap to a 18k resistor,and r-40 from what looked like a blue resistor with a black band in the middle.it read 0.00 both ways on the ohm meter to a 3.9k resistor as shown on the print.i still have hum and also a hi pitched squeal.if i scope the ic chips in the preamp i get a sine wave on the first ic then the next ic looks simular with a little deformation with the middle parts missing on both sides.i noticed with the scope that if i probe the negative speaker lead i get a square wave pattern with the function generator set for a sine wave.when i probe the positve speaker lead i get a dc type pattern that jumps off the screen till i reposistion it.it looks irregular shaped tatterd.i smelled a small burnt smell after running it for awhile.might be r-40 as my guess since there was no resistance there earlier. i think i'm going to put the circuit back to what it originally was as it might of been a factory mod. i noticed the hum goes away when i turn down the guitar or unplug the guitar from the input.if i touch the treble pot on the amp or the  metal guitar tone control it squeals.i will read your last post and try to figure out what you mean and after putting the circuit back to where it was try to locate the hum area....