5150 Problem. any gurus

[BLOODROOT]

Ok. So I've been having problems with my 5150. its not the tubes Ive tried multiple sets. Whenever you turn it on it works for a bit then the volume goes way down and is stuck there no matter what you put the volume nob. Does it on each channel. Im you give it a smack then it works again. I know that isnt good. but thats not the issue. I took it to rehearsal the other night and all the sudden i got a loud hum that wouldnt go away until i unplugged it for a few minutes. Also if you have it going and unplug the cord, it hums at whatever volume the amp is on. real loud hum. it goes away once you plug back in but if you stop playing that hum is there faintly. The amp is ok once you get it going but cant take it to any gigs. Gotta take the engls for that. Ive taken it apart sprayed all the pots with contact cleaner but didnt fix the issues it has. Anyone experience this. I dont want to take it to the shop and pay an arm and a leg if its something easy. Ive also done the whole cord in the send to the return. Even unplugged the loop all togethe from the board and it still does it. I dont see any burn marks or bad solder joints. shruggs.

Kris.

 

[TravisW]

Sorry to be redundant, but did you replace all preamp tubes as well as power amp tubes?

 

[Metaltastic]

Hmm, yeah, +1 to Travis, though if you've checked all tubes and done the whole FX send/return contact cleaning to no avail, then something else seems amiss, and I'm out of ideas!

 

[stevehollx]

You have to be more specific on the troubleshooting that you've done.

"Also if you have it going and unplug the cord, it hums at whatever volume the amp is on. real loud hum."

What chord are you referring to? I hope it wasn't the speaker cable. When there is no instrument cable in, the jack should short the signal to ground, so you should hear no hum whatsoever. If you hear a hum with the cable not plugged in, chances are you have a bad ground somewhere, or the signal path isn't connected somewhere between the input jack and the phase inverter.

You say you tried the effects loop test. Need more detail on what you tried. Take your Engl, and plug the preamp out (effects send) into the power amp in (effects return) on the 5150. Does it sound okay? If so, the issue is with the preamp. If not, the issue is with the power amp. Then try the reverse (5150 preamp into Engl poweramp). That will help us narrow down the issue.

How old is the amp? Over 10 years? Maybe the filter caps are going. If the amp warms up fine after some time, my guess is the issue is here. Is the amp lacking some low end punch recently? Are you comfortable pulling the chassis and taking pictures of the filter capacitors (typically the big plastic coated tube looking items)? If so, ususally when these start to go they start bulging or oozing. If you decide to pull the chassis DO NOT TOUCH ANYTHING inside the amp since the filter caps can store a FATAL charge for days. You can also visually inspect for burnt components, cold joints, etc. If you have a wooden chopstick (non-conductive) you can turn the amp on high gain and poke around. Usually if you get a bad joint and poke it, it sounds like demons are trying to scratch their way out of your amp.

To be honest, if you don't want to take it to a tech, get busy learning how tube amps work, and it will probably be 3-6 months before you'd be able to effectively troubleshoot the issue. And even then, you'd potentially need an oscilloscope depending on how complex the issue is.

I know the way the 5150s are designed there is a piece of metal that holds the preamp tubes on the PCB that can arc. It may not be a bad idea to try and insulate that with something. But again, stay out if you aren't comfortable with being inside something with high voltage and current.

Happy debugging.

/s

 

[Loren Littlejohn]

Man, just take it in. It could be something stupid, it could be something simple. Either way, amps should be seen now and then anyhow.

 

[Fredrik-Ablaze]

Have you checked the solder joints on the tube sockets?
Take it to someone who nows his soldering and have him resolder the whole amp, sounds like a bad solder joint somewhere to me.

 

[NickL]

I got my 5150 for 400 because it had this problem and contact cleaner fixed it. No more problems in over a year MAKE SURE TO CLEAN THE FX LOOP even if you dont use it

 

[BLOODROOT]

You have to be more specific on the troubleshooting that you've done.

"Also if you have it going and unplug the cord, it hums at whatever volume the amp is on. real loud hum."

What chord are you referring to? I hope it wasn't the speaker cable. When there is no instrument cable in, the jack should short the signal to ground, so you should hear no hum whatsoever. If you hear a hum with the cable not plugged in, chances are you have a bad ground somewhere, or the signal path isn't connected somewhere between the input jack and the phase inverter.

You say you tried the effects loop test. Need more detail on what you tried. Take your Engl, and plug the preamp out (effects send) into the power amp in (effects return) on the 5150. Does it sound okay? If so, the issue is with the preamp. If not, the issue is with the power amp. Then try the reverse (5150 preamp into Engl poweramp). That will help us narrow down the issue.

How old is the amp? Over 10 years? Maybe the filter caps are going. If the amp warms up fine after some time, my guess is the issue is here. Is the amp lacking some low end punch recently? Are you comfortable pulling the chassis and taking pictures of the filter capacitors (typically the big plastic coated tube looking items)? If so, ususally when these start to go they start bulging or oozing. If you decide to pull the chassis DO NOT TOUCH ANYTHING inside the amp since the filter caps can store a FATAL charge for days. You can also visually inspect for burnt components, cold joints, etc. If you have a wooden chopstick (non-conductive) you can turn the amp on high gain and poke around. Usually if you get a bad joint and poke it, it sounds like demons are trying to scratch their way out of your amp.

To be honest, if you don't want to take it to a tech, get busy learning how tube amps work, and it will probably be 3-6 months before you'd be able to effectively troubleshoot the issue. And even then, you'd potentially need an oscilloscope depending on how complex the issue is.

I know the way the 5150s are designed there is a piece of metal that holds the preamp tubes on the PCB that can arc. It may not be a bad idea to try and insulate that with something. But again, stay out if you aren't comfortable with being inside something with high voltage and current.

Happy debugging.

/s

Oh sorry i wasnt explicit enough. oops. yes the amp is plugged into a speaker cabinet with a speaker cable. I was talking about, lets say you are playing the amp. it is sounding ok. You pull the guitar plug out of the input. It hums really loud.The louder the volume nob is turned up, the louder the hum. The efx thing i was talking about was plugging a cable from efx send to efx return and it didnt help. I read somewhere that peaveys are notorious for issues with the loops. shruggs. I will try the preamp out to my engl efx return and see. I already have the chasis out of the box. I dont see anything wrong with the filter caps. I will post pix later. When the amp works it sounds great. im not against taking it to a tech. I just wanted a bit of info first. My brother in law is going to look at it when he is in town. He is an electrical engineer. Although that doesnt make him an amp tech. I figured he could look at and know what to touch, what not to touch and what to solder. if all else fails, I will take it in to be fixed. Its a block letter and I kinda wanted to keep it untainted but oh well. Plus probably cost 200 bux to fix, grrrr

 

[greyskull]

sounds like a sketchy pre amp tube, or a preamp tube that is not sitting in the socket preoperly.

 

[axeman720]

Next time it does it push on the preamp tube circuit board and see if it comes back. The connection can come lose over time and the usual main culprit of the problem is the preamp ground screw. Sounds like the hum is probably ground noise and its likely this is the problem, but who knows? Just about any authorized peavey tech will know about this problem.

Hope this helps

 

[SuperD]

MAKE SURE TO CLEAN THE FX LOOP even if you dont use it

What he said