Wow, I knew it was bad, but I had no idea it was that way. I mentioned it to the owner of the school (we rent the building) yesterday, and he seemed surprised that I had even mentioned it. He said "how did you figure that out, what happened?"  He has a more that healthy fear of regulations, so I'm hoping it's fixed soon.

Right now all the outlets on one side of the building are correct (next to the front desk and the waiting area) and all the other outlets (in the actual studios) are open ground, or open neutral. All the ones on my side of the hall are open ground, so I'm hoping it's one outlet upstream that needs to be fixed. I'll post about this again if I take the amp home and test it if they , I mean WHEN they fix the building

So it took me a while, but I got an outlet tester. And of course it reads open ground.

I never turn the volume or post gain past 2, and only to 2 when I'm the last one here. Clean channel with no verb is tolerable. Dirt channel with gain to about 3 and no verb is also tolerable. Past that it gets progressively worse, but I'd expect that.

Turning up the reverb on any channel is dicey. At any volume level. Hums like mad when it's set to 10. This stinks as my favorite sounds are drenched in reverb and delay. I can live without it but, still, that's a disappointment.

As far as the cell phone, I should be more specific. I use it as a tuner, recording machine, tab encyclopedia and so forth. So when I get the interference, it's cellular data. I'm using edge network, which seems to be the issue. The music store recently fixed their wifi, so when I switch to airplane mode, I don't seem to have any problem there.

I'm guessing with an open ground every cable I have is now an antenna. Boo. I'm wondering what the wiring looks like behind the outlet, but I need to ask the management before I attempt to fix it. Anyone have any ideas about remedies that don't involve modifying the building?

So, because people here have been so good to me, I thought I'd pose another riddle. I have a silver stripe era peavey studio pro 112. It mostly sounds great, but I have a small problem. In my lessons studio it seems to pick up a lot of interference. My previous amps in that space, a crate gx40c and g60 picked up some, but not this badly.

There's some 60 cycle hum and a bit of noise from fluorescent lighting, but that's not the worst of it. My cell phone (the fruit brand) drives it nuts. Turning up the reverb is like turning up the hum. Can I add shielding to the enclosure? Maybe shield the reverb cables or tank as well? What are the risks? Thermal issues? Microphonics?

Also, for bonus points, a previous owner removed the handle on top. Something else leaked through the hole and so now a jumper wire and a transistor(?) next to the main heatsink are corroded. They seem to work, and if sometimes the dirt channel doesn't work, a swift blow to the chassis brings it back in line. I'm inclined to leave it alone. What are the chances that's contributing?

Success! Thanks to you guys, I got everything working again!

I did end up going with the 4558, as it was easy to get and I didn't want to worry about pin assignments. I used desoldering wick to take off 80-90% of the old material. I popped it in, carefully resoldered and turned it on. JOY! Two blinkenlights!

Soundwise the dirt channel is meh. But hey, now it works! I like my peavey's "transtube" gain better so I don't think this one will become the daily driver. Having said that, I learned some new things, and I'm very happy.

Well, first I scrubbed the board, and then I replaced both resistors and the cap. Nothing changed, so I tested IC1. If pin 1 is the one closest to the dot (upper left) and pin 8 is on the opposite side facing the pots (upper right), I got:
1. cold
2. cold
3. cold
4. (bottom left) -15
5. (bottom right) cold
6. -15
7. -15
8. +15

Checked the one zener diode I could find on that side, and it has voltage on both sides.

?

Thanks guys, I'm going to crack the amp back open as soon as I can, in the meantime, here are the pics of the nasty PCB. I would buy Deoxit, but I'm already in the hole on this one, so there's $13 I don't want to spend if it won't help.

First, thanks for all the ideas! I'm glad to have any help in this case.

I am so confused. So, there are no numbers to indicate which component I'm dealing with, so I'm having a hard time tracing circuits to find test point 9. And I do realize that not every board is completely numbered, but this one has nothing!I'm used to bending on cheap keyboards and pedals, where at least the caps and transistors are labeled.

But, I did test the clipping LEDs and noticed that one ( I think the second one in the circuit, it was closer to the clean channel ) stayed ON. And BRIGHT. The other one, dark as night, not even a flicker. I'm going to try and post pics.

Cue the trombone and muted trumpet music. So I swapped out Q3, it tests fine now, but no joy. Dirt channel still lights up, still makes no sound, clean channel works 100%, verb is working as well, fx loop has no, well, effect.

I'd still love to fix it just on general principle, but I gave up and bought a Silver Stripe Peavey Studio Pro 112 on CL. Paid $50 for it, so I don't feel bad about it.

If anyone has any more (cheap) ideas, I'm keen to try them. When it comes to debugging PCBs with more than 10 components, I'm not an expert, so I'm done otherwise.

On a related note, if anyone in the Atlanta area wants a pet project with a U.K. made celestion in it, let me know. 

Well, from the you-told-me-so dept.

I put a - probe on the middle leg of all the transistors on the preamp board, and then touched the + to each outer leg. There was super high resistance on one side, and almost none on the other. Until.... I got to one in between the two channels and right next to the switch on the front panel. The needle didn't even twitch. Double checked it, same result. I didn't have time to turn over the PCB, but my money says it's probably Q3, given the location on the schematic.

Now I just need to see if my local supplier (ACK supply) has one 2N5638 on tap. All the datasheets say that it's "end of life" and "limited supply" but that's what they say about the MPSA13s I use for every fuzz pedal build.

Ok, so I swapped the reverb bag cables - got a crazy hum - swapped them back - it started working?!? how is that even possible? I guess I won't ask any more silly questions.

I put a dummy load on the fx loop, no change. plugged the gtr straight in to line in, and got a lower output clean sound. I checked the schematic. It looks like the loop ties straight into the power stage.

so, to sum up
Clean channel - check
'Verb - check
Loop - check
Dirt channel - lights, no sound.

as promised, I'm attaching a schematic

Oh, I didn't even consider the fx loop. I assumed that it bypassed the tone stack, and somehow that would be the issue, but now that you put it like that, I'm not sure how I got to that conclusion.

I haven't tried swapping the plugs on the reverb, because I'm not used to working with higher voltages (mostly pedals and pickups) and I didn't know if that would fry something. I guess i've got not much to lose at this point.

I do have a schematic, I got it searching for the owner's manual. It's on a different computer, so I'll have to follow up on that. I'll try those ideas as soon as I can turn up the amp without pissing anyone off

So I picked up a crate g60 as part of a CL deal, looking for a good SS amp to serve as a small PA, gig amp and lesson studio knock around.

At first it hummed like crazy, but that was fixed by simply removing the power stage and cleaning the chassis a bit (it's crazy rusted with bug bits inside).

The reverb is wimpy and the distortion channel lights up, but has no output.
The most sophisticated diagnostic gear I have is an analog meter. Should I even mess with this thing, or toss it back into the CL pit?