Okay, I posted this in the G&A forum, but I thought I'd post it here as well because I thought more electricians/circuitry wizards might hang out here.

I have a Peavey Valveking 112, which has two inputs; a high gain input and a low gain input.

Generally, I have always used the high gain input on my amp, playing a Les Paul Studio. However, during a gig recently the high gain input just... stopped working. There is a dull hiss being emitted when on the distortion channel, but no signal. The low gain input works fine, but doesn't really live up to what the high gain input could do for my style of playing.

Seeing as though the low gain input works just fine, I presume that my amp hasn't blown?

Could the input jack be broken (easily fixable)

Or could this be something more serious with the circuitry (not as easily fixable...)

I know the answer is indertiminable without seeing my amp, but what do you guys think/suggest I do?
im not too familiar with that schematic, but i'd say check the jack first, then see if the high gain has its own preamp tube, because that might be the problem, but i think that its just a jack problem, usually they use the same tube and just allow more signal to hit the preamp..
It can't really be determined without further testing. On several models, Peavey has an additional stage of gain on the high gain input. Could be just the jack. Could be the ribbon connector on the printed board. Could be the first tube (valve). Replace the first preamp tube. It's the easiest thing, so start there. If the problem goes away, you're done. If not take it in for repairs.
Quote by Jackal58
I release my inner liberal every morning when I take a shit.
Quote by SK8RDUDE411
I wont be like those jerks who dedicate their beliefs to logic and reaosn.
This sound like an open circuit, so look out for bad solder joints or disconnected wires inside the amp.

Then, move on to the first preamp tube and look for white spots on the inside of the glass envelope; this indicates that somehow the tube has been damaged and air is getting inside. Change the tube immediately if it's the case.

It might also be a bad coupling capacitor on either the input or the preamp's output that blocks the signal. This one might be a little difficult to find without proper instruments (i.e. an on-circuit ESR meter like this one calibrated to deflect properly with the capacitor's nominal value), but you can always take a look for physical damage on the capacitor itself.

A blown resistor might also cause your problem, look for burned marks or again for other apparent physical damage on the resistors related to the preamp (input resistor, anode and cathode resistors, etc.).