New Guy, 5150 question.

[Danglin' Fury]

I recently started a sideline amp repair biz and I have come across the dreaded Peavey 5150. The guy I got it from spilled a cup of coffee w/ heavy sugar into the 2x12 combo. I cleaned the boards thoroughly and allowed ample dry time. Before this, the amp would come on and hiss but no sound. I have a bit of experience w/ tube amps as I own a JSX and have fixed several Peaveys. Since cleaning and reassembly, I get sound now. The channels sound how they are supposed to but the volume is barely there. Like it's on 2. The pre controls work perfectly for both channels but the post controls show no change until you get to 9 then it sounds like an amp on about 3 or 4. The reverb doesn't seem to work and the high acts like a mid boost when turned to 0. Very strange. Any suggestions on where to start Ohm-ing. I tried the cord in the effects loop thing to no avail. Any suggestions welcome as this guy needs his amp next weekend for a gig.

[Twist]

Do you have a schematic? You might line out from the effects send to another amp to see if the problem is in the pre amp. And likewise take a signal from another amp to the effects in on the Peavey to see if the problem is in the power amp. If you plan on doing much amp work invest in a signal generator. I'm located just east of you in Springdale Arkansas. I used to talk to David Hicks over in Tulsa on occasion.

[Amp Kat]

Verify all the preamps tubes are working and maybe wiggle them with a guitar plugged in and the post up to see if you can get the power back. Have you ohmed out the Output transformer ? Not trying to stir up notion but that is a symptom of a bad 5150 OT. If it's good I'm thinking a connection but first I would do what Twist said and Isolate your problem to the preamp or power amp section.

[Danglin' Fury]

Thanks for all the replies. I have tried the tube wiggle thing. I also put the 5150 tubes in my JSX and it sounds fine so the tubes are good. I also put my JSX tubes in the 5150. Same problem. I talked to a local tube amp guy, Rick Potter, and he said it kind of sounded like the phase inverter wasn't working properly. I'll check the Output Transformer and try to isolate the problem to the pre or power amp. I have measured the voltages to the power tubes and they are consistent. I also get that sweet blue glow of the electron beam when I kick it off standby. Once again thanks for the replies and if you think of anything else, please let me know.

[drewl]

Did you isolate the preamp/poweramp sections or see where the volume is dropping out?
FWIW I had one with a bad ground and an intermittant voltage dropping resistor board connection which behaved in a similiar manner.

[Enzo]

Plug the guitar into the effects return. is that reasonably strong or still very weak?

[Danglin' Fury]

Thanks Enzo. I plugged my git-fiddle into the return jack and the signal was VERY strong. So now I'm pretty sure it's the pre. I came across a schematic and noticed the most concentration of the coffee funk was around R99 and R100. Also C56 and C57. Those connect to some major voltages to the pre tubes. I'll check there and let you know what's up. If you think of any more suggestions, please let me know. I REALLY appreciate all your help, guys.

[Amp Kat]

Are you talking about the flux build-up or is it liquid ? R-100 is right at the preamp out so try the preamp out and see if it works into the front or return of another amp but make sure the post is above 3 or it will get real thin. There is a cable also one of the gray ones going to the preamp tube board. Inspect that cable real well for burn marks at the base of it where it goes into the board on both sides. Seems like it may be right around that preamp out section where maybe something was connected into that jack that was a little hot maybe.

[Danglin' Fury]

Are you talking about the flux build-up or is it liquid ? R-100 is right at the preamp out so try the preamp out and see if it works into the front or return of another amp but make sure the post is above 3 or it will get real thin. There is a cable also one of the gray ones going to the preamp tube board. Inspect that cable real well for burn marks at the base of it where it goes into the board on both sides. Seems like it may be right around that preamp out section where maybe something was connected into that jack that was a little hot maybe.

No, it's definitely coffee. The guy I got it from spilled half a LARGE cup of coffee w/ heavy sugar.I cleaned it al off and found a schemmy and just as I was about to become The Ohm Ranger, my meter crapped out. By crapped out I mean it reads .12 volts across 3 different 9 volt batteries.

[Danglin' Fury]

New Guy, 5150 Q: still need help!!!

I have isolated the problem to the preamp. I have a schematic and at v3+ I have my 440 volts. At v2+ I'm supposed to have 300vdc but I have 380. At v1 I have 360vdc. I talked to a guy @ Peavey and he said remove Q1 clamp circuit as that could cause some failure if damaged. I have Ohmed the pre board and have seen some strange resistor values, substantially lower than the schemmy says. He also said if the coffee spilled into it (which it did hit some of the plate resistors the voltages would act in this fashion. Somebody PLEASE tell me I'm onto something. Thanks for looking.

[Enzo]

Hi DF. Please don't start multiple threads for the same amp with the same problem. Just post on the original thread. It makes it a lot harder to help you this way. I don't remember what the original problem was adn will now have to go find the other thread to find out.

When measuring resistors in circuit, you will usually get odd readings, and they will almost always be lower. This is because ther are parallel circuit path around most parts. Also, sometimes ther are small residual voltages left in caps, and those interfere with meter readings.

So, did removing Q1 make a difference?


Are all the tube heaters glowing? Check each one. WHat plate and cathode voltages are present in the preamp tubes?

[Danglin' Fury]

Hey guys, sorry about starting 2 threads , I was a little toasted last night. I removed Q1 and it got worse. Now when I plug into the effects return jack, I get nothing. I can still hear sound coming from the amp and the channels are different in sound but the signal is very weak. The plate resistors read good and my reverb still doesn't work. I am going to try to replace the Q1 and see if that makes a difference. Now it seems 2 of my pre tubes aren't being activated as they are not glowing. One of them is V3 and isn't that the effects loop buffer? These amps are fat turds to work on. I have fixed a few Peavey tube amps before and I've seen nothing like this. The voltages that I am getting at the voltage divider after the rectifier like I said previously are still out of whack. The 440 is there but R99 is supposed to drop 140 volts taking V2 down to 300. It only drops 60 volts so it puts it at 380. R100 is supposed to drop 20 volts and it is but instead of it being 280 it is 360. One would think R99 would be the culprit but nay, it isn't. That resistor is supposed to read 220k ohms and out of circuit it does. Could the cap be bad? I'm thinking about telling my buddy to throw this amp in the river as this is very frustrating. There has to be an obvious open to increase the voltage in the divider but I can't find it. I can't find anything shorted either. If anybody has a clue to my problem please give me a hint. This may well be my last 5150 to work on.

[Mars Amp Repair]

I haven't had time to find theoriginal thread, but coffee or beer for that matter under the tube sockets on a pcb can cause all kinds of weird connections between the pins of the socket.
You probably have to removed all the tube sockets & really clean them as well as the pcb to completely eliminate any errant resistances as a result of the coffee.

Other wise you're going to be chasing issues like this forever & probably even after you return the amp as the coffee traces begin to cause more bridging issues.

I had a Mesa like this where it worked for quite a while for the cust after it 'dried out'. I pulled the board, which as you know on a Mesa is a major procedure, & found the pcb actually burning between 2 pins. glen

[Amp Kat]

I haven't had time to find theoriginal thread, but coffee or beer for that matter under the tube sockets on a pcb can cause all kinds of weird connections between the pins of the socket.
You probably have to removed all the tube sockets & really clean them as well as the pcb to completely eliminate any errant resistances as a result of the coffee.

Other wise you're going to be chasing issues like this forever & probably even after you return the amp as the coffee traces begin to cause more bridging issues.

I had a Mesa like this where it worked for quite a while for the cust after it 'dried out'. I pulled the board, which as you know on a Mesa is a major procedure, & found the pcb actually burning between 2 pins. glen

Couldn't agree more with that. It will haunt you if you don't do it.

[Danglin' Fury]

I replaced Q1 clamp circuit and took all the tube sockets off the PCB and cleaned them even more thoroughly than before. No good. I noticed me V3 (effects loop buffer) and my V5 (reverb?) tubes are not lighting up. They are cold to the touch too. I placed my leads across the pins of C44. It dropped the entire voltage generated @ V2. When I put the leads across the cap pins, The board w/ the rectifier made a popping/squealing sound. I wonder if this is the culprit?