Kustom PA 200 very loud hiss on output

[JerkyPudding]

I have a Kustom PA 200 head with very loud hum and very loud reverb crash in the output, even with all preamp and reverb volumes turned down. It seems like there is excessive gain on the output, the noise floor is very high. Thoughts?

[J M Fahey]

In principle only way to have lots more gain than original is to somewhat have lost NFB at some later stage.

If you can post or lin the schematic we might look what gain stages are there after the reverb tank.

Did it appear suddenly or you got it that way?

Did anybody touch/mod/try to repair it?

[52 Bill]

If there is a loud hum, you first need to figure out why that is.

Is there any DC voltage on the speaker output?

[JerkyPudding]

Here are the schematics for the output stages. A friend of mine purchased this amp online, it has always done this to him. I can see no signs of mods or any kind of work done to it. It looks to be very clean, with one exception: it looks like a critter chewed some insulation off a ground wire, and there's plenty foul odor/dried muck inside. I'll look closer for further damage. The amp operates fine beyond this high gain. Thanks for the reply.
PC703.pdfPC803.pdf

[JerkyPudding]

There's no hum, just the normal Kustom hiss, but it's very loud, as is the reverb crash.

[52 Bill]

There's no hum, just the normal Kustom hiss, but it's very loud, as is the reverb crash.

Divide and conquer, find out if the main source of the hiss is the power amp or the reverb mixer board or the individual preamps.

Try grounding the input/output jack on the back panel and see if the amount of hiss changes.