First of all, you need to be aware that this amplifier configuration is called 'The Widow Maker'.
The ac mains voltage is directly coupled to the rectifier.
There is not a transformer to supply the secondary voltages.
To work on and operate these safely you must have an isolation transformer that would separate the mains voltage from the amp (110-110Vac)

Follow the signal into the power amp.
You do have a scope, correct?
What does the signal look like at the base of Q8?
Q10?
Q11?
Q12?

So you feel the output is 'low'.
What is the maximum Vac out into an 8 ohm load before clipping?

Other than having the designators wrong on the outputs and the leg assignments wrong on the Negative outputs, I see nothing majorly wrong with the static voltages.

The schematic indicates a 225mv AC signal entering the amplifier.
What value do you read coming in there?

Where is the schematic?
Can you please post it?
On the last three transistors, what are the designated 'Q' numbers?

Not too sure what you are attempting to fix here.

Yes there is a small x over notch at higher settings.
I really doubt that you could here that.

What I see from the image is a gross mismatch in the top & bottom width of the waveform.
THAT will be noticeable.

Can you take a picture of the distortion as it appears on a scope?

If so, upload it.

The issue needs be to better defined.
Shuts off as in the front indicator goes out?

The rear tab on both ic's, both boards, is connected to the B- power supply.

If the heat sink is 'floating' and not at ground potential then there is no need to isolate the tabs.

As to bridge mode, I am not sure.
They appear to be stereo amplifiers.

According to the schematic, there are two pots that need to be adjusted.

Have you attempted to contact Rocktron?

http://www.rocktron.com/contact.html

I believe that the OP is referring to the Foot Switch jack.

Can't seem to find a schematic for that amp.

My first thought is try to find the correct plug.

The KA2206 is a 2 channel power amp.
It is rated at 4 watts output with a 12Vdc supply , into a 4 ohm load x2.

I have seen them on keyboards.

Being that the JC 120 is a solid state amplifier, there is not any need for a dummy load if you disconnect the speakers.