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Okay, so I made a thread a while back about hearing some weird clipping noises coming from my Kustom "Defender" (15 watts, one 12AX7, two EL84) when I played my TurboRAT. I decided to test it with both my TurboRAT and Behringer VD1 Big Muff copy. On my other amp, a Kustom "The Contender (18 watts, one 12AX7, SS power amp), I was able to turn the gain and volume up on both pedals without noticing any anomalous clipping or volume drop. Today, I tried again with the Defender and the Behringer cranked right in front of it. The amp was set clean and I had the Behringer at unity gain. When I turned the volume up on the pedal, the volume of the amp fizzled out, and remained like that, even when it was just a 15 foot cable between the amp and guitar. I'm going to try with my other cable just to make sure, but I'm very certain that it's the amp. I also turned the volume all the way up to see if I could hear anything, and I just barely heard my guitar, and it sounded overdriven like it normally would be.

I'm obviously going to need to get it taken to a guitar shop around her to get it fixed, but can anyone tell me what might be the problem here? It's never been dropped (at least while I've had it, I don't want to know how it was handled during shipping), the tubes are all glowing normally, and I rarely ever had it turned up enough to overdrive the tubes (except for when I first got it and today, when I turned it all the way up after the volume went out).

If the guitar sounds fine going into the amp by itself, and it fizzes out when there's a pedal in the middle, how could it be the amp? It's probably the pedal.

I must have said something wrong; it's fizzing out regardless of there being a pedal or not. I cannot hear it unless I turn the volume up all the way, and even then, it's just a whisper. It's overdriven as it would be when cranked, but it's at whisper level.

Oddly enough, when I went to demonstrate this on camera to upload to Youtube, it started working again. I suspect that the original issue is still present and it will fizzle out again if my distortion is turned up past unity gain. In fact, I think I might go test that right now.

EDIT: Oh, and now that it's working again, I went to turn the volume up to see if it would do the same thing again when overdriven and I was correct. It's fine when it's clean, but if the amp is overdriven, then it starts messing up. I will record it now.

EDIT: Oh, for fuck's sake. It's gone back to being quiet.

Here's a video demonstrating it:

[youtube][/youtube]

Many possibilities.
If you have an FX loop, trying plugging a cable from the send to the return. Some amps have a problem with the jack sockets, especially if it's a few years old. Otherwise - bad solder joint, cracked PCB track, faulty tube, intermittent short due to debris, intermittent short due to bad lead dressing.....

run a signal through it and jiggle preamp tubes (i think this might have only one?) and see if you hear any change

It could well be a bad tube. My DRRI died on me at the end of practice this evening, and sure enough...one of the preamps isn't glowing like the others (V3, a 12AT7 that's the Reverb Send, apparently). Hopefully that's all it is.

Looks like I'll be heading into town to pick up some spares and a set of fuses, just in case. Which I really ought to have stashed in the house already.

I jiggled the preamp tube as much as it would allow and got nothing. It's still glowing and everything. I decided to check if it was maybe the speaker or speaker cable, so I plugged is into the Kustom Contender and discovered two things:

• 1. The speaker and speaker cable were fine
  2. The Contender sounds fucking awesome and clear through a 10 inch Celestion speaker, as opposed to the boxiness of the stock 8 inch Kustom speaker.

Now I've gotta buy a cab with two good 10" speakers to make the Contender into a twin combo.

But I digress, what do? I already yelled at it and poured beer on it too.

I would say tubes even though they seem fine. When my Twin was acting dodgy I swore something was loose or fucked otherwise, and the preamp tubes were brand new, but it ended up being one of the brand new tubes was bad and two power tubes were going out.

Tubes can act all kinds of nutty, I put my bet on preamp tubes.

I sent a message to my friend's guitar tech, he's coming by later at 6 to pick it up. I'm willing to bet it might be faulty tubes as well.

I just now had the idea to switch out the preamp tubes in my Contender and Defender, and I learned that it's definitely not an issue with the preamp tube.

I don't know if it's just placebo effect, but the Defender 12AX7 in the Contender sounds better than the stock 12AX7B.
On the other hand, the Defender still does not get any louder. So now, I'm thinking it might be some faulty wiring somewhere, or perhaps the power tubes?