As a technician, I don't expect failed parts to look any different.  Once in a while they do, but not usually.

You probably do have a failed speaker.  It could be a voice coil wire coming free of the former, it could be a warped voice coil, it could be a variety of things inside.

Pull the speaker for testing.   Here is one simple test:

https://www.youtube.com/watch?v=31768KUK9K8

Oof course also first make sure no wires are touching the rear of the cone.  MAke sure the mounting bolts are snug. and make sure the terminals on the speaker where the wires connect are not cominbg loose from the frame.

When you asked the postal service, what did they tell you it would cost to send a padded envelope on that trip?

I suggest making the amp work before even thinking about mods.

Do nit assume it is a bad component.  It could be, but could also be a broken connection, broken wire, cracked circuit trace, etc.   Apply a signal and trace it through the channel looking for where it disappears.

My first reaction is a bad semiconductor somewhere.

Never lose sight of the fact this is just a guitar amp, not lab equipment.   And a lot of those audio discussions are from hifi people whose goal is an amp flat from almost DC up to radio.  Totally not needed even for them and certainly not for guitar amps.

Faster?    Unless you are amplifying radio signals, I am not sure what faster would get you.

No pictures?   Reread your typo in your previous post.

"Dirt" in the jacks does not refer to visual grunge, it refers to electrical dirt.  Contact surfaces oxidize or build up a film of foreign matter.  This happens to ANY amp of ANY brand that has FX loop jacks.

You need to clean the cutout contacts, not just the parts a plug touches.

There should be an FX loop on the rear.  Lower right corner.  Just below the FS jack.

If patching a cord across the FX loop restores the sound, then your return jack needs service.

I see R317, connected to C ot Q304, but I don't see R339 anywhere, help me out.

The voltage at the bottom end of R317 is controlled by Q303 (including the 2v through Q304), which in turn is controlled by the diffy pair.  It seems that the diffy pair is turning on Q303 too hard.

The voltage at C of Q304 is so low because the voltage at C of Q303 is so low.  Q304 is working, as it is keeping the 2v difference across itself.  Q304 simply follows whatever C of Q303 does.  The reason C of Q303 is so low is what Loudthud is trying to help you with at Q301/Q302.   They control Q303.

Yes, I DO miss things, it gets harder and harder to focus any more.  Sorry in advance.

Q303 VE 1.9v?  Yet it should be at ground.  Where are you grounding the meter?

HAve we checked the positive rail is available through R316/317 ,top center?  Open up there and there is no voltage to pull Q303C back up to anywhere.

Your output seems to be tracking the collector Q303, which is what it i ssupposed to do.

OK, remember, whatever is on the bias transistor will be within a couple volts of the output.  The bias transistor circuit controls where the output goes.

It sounds to me like the bias circuit works, whatever you have done to this thing, the output always tracked the bias transistor within a couple volts.  That is how they work.

Zener diode "seems like" it is working?  It is a protective device here, you can unsolder and lift one end if you suspect it.

The output can sit at most any voltage and not draw excess current, because there is no load on the output to draw that current.

OK, so Q303 does seem to control the voltage on the output

You have the 80 at the collector of Q30, and may I assume also at collector Q303?

So wwhat is happening at the base of Q303?

The parts list shows 1N4731A OR 1N5229.

From here it looks like the right half of the PA is working.  Your bias transistor Q304 has a couple volts across it at all times if it is working.   And it runs the whole power stage.  Within a couple volts, whatever voltage is on Q304 is what will appear on C404.

Q303 is not a resistor, and a resistor will not operate as a transistor.

Bar of alloy bolted to the chassis?  The chassis is part of the heat sink.