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Measure DC voltages (no signal) at points A through G.

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That string of parts marked in red sets the bias for the drivers and in turn, the output transistors.
Was D6 the same type as D4 and D5?  Black plastic like 1N4001 rectifier diode, or glass type like 1N4148 signal diode?
Replace with same type it was (signal or rectifier).
While you are there I would resolder all connections in that bias string.
That sounds normal for the thermistor.  Make sure neither of it's legs are touching the heatsink.

Quote from: DrGonz78 on June 06, 2024, 01:20:00 PMI don't know what Q11 & Q12 actually do but it never stops me from guessing. Are they current limiting the circuit in case of overload?
Unfortunately, this is one of those 'flying rails' designs which makes things a lot more confusing.  The output transistor emitters go to ground, and the positive terminal of the output jacks connects to the center point of the main filter caps (marked 'CC' on schem.)
So a bit of reverse logic as far as how the speaker fits in the circuit.
As long as you make your voltage measurements to ground, they should be ok.
At the input to the power amp, shown to the left of U1B, there are 2 diodes, D1 and D2.  You should measure 0VDC at D1 anode/D2 cathode.
Is U1 in a socket by chance?  If so, clean it.
Ok, if it's your own amp you can leave it like that.
Just mentioned in case it was going to someone else.  Don't want to have to change your name from mr. to Dr.  ;D 
Q14 doesn't seem to be turning on, probably resulting in cross-over distortion which Dr.Gonz suggested.
Check through the components (and connections) on the path shown in red here:

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It would be preferable to mount the other way if possible, with less exposed wiring.
The 2 black wires are carrying the 120V and you don't want any chance of a user being able to come in contact with them, or for them to get damaged.  Also, if those wires are not going through an original hole, the new hole can not have any sharp edges.
If you can, flip it over and mount so the 2 black wires are closest to the hole the wires route through.
Aside from that, the FM65 transformer is a great match for voltages and power capability (for Bandit 65).
Yes, that is where to check.
If no DC there, check DC volts at e,b,c of Q6,Q7,Q8,Q9.  No signal, no load.
That's great you didn't have to do any drilling, and no excess hum.
What transformer did you end up using?
Those seem good.  Can you do the same checks (DC volts, no signal) for e,b,c of Q13 and Q14.
5V 1Khz signal is way too much.  50mV would be a better level.
But for DC static voltages you do not want to be applying any signal at all.
Recheck DC at Q8 and Q0 with no signal applied.  And check the pinout, it looks like you have the emitter and collector readings reversed.
Another thing to try would be a patch cord connecting FX send to FX return jacks.
Quote from: Frank75 on May 27, 2024, 08:18:36 AMAs soon as I moved the volume pot I lost, say, 80% power.
Have you cleaned the pots?  If not, do so. 
If you already have cleaned them, it sounds like the volume pot is defective or needs to be re-soldered.
Thanks Jazz.   :)

Quote from: on May 23, 2024, 05:44:09 PMPardon my inexperience. How would I do that without providing a URL?
When you are in the 'quick reply' area click on the 'preview' button.  There will be an option to directly attach your files here.
Bad caps should not make the supply voltages read high.
Getting the correct power supply voltages should be your first step.  You might be lucky enough that it solves all your problems.

I can't access dropbox files.  Could someone please attach the power amp and power supply schematic from the first post?