Problem with my 5150 squealing

[JakeAC5253]

I've had some preamp tubes lying around for a while and I've been swapping them in and out of my 5150 in different slots lately. Today I am having huge problems with feedback even at low volumes and gain levels. It seems to be aggravated by stepping on any type of boost pedal and the squealing is horrible, much worse than your average high gain type feedback. The squeal only seems to go away when you lower the gain to below 3 on the dial. If you sweep the knob past this point really slowly you can hear the pitch of the feedback coming down. Easy right? Microphonic preamp tube, it's gotta be.

Here's what I've done so far:

I took a pencil and tapped each one of the preamp tubes and nothing really conclusive happened. I tried the power tubes next, still nothing. Then I looked closer at the preamp tubes and saw that two were distinctly dimmer than the others... and they happen to be the ones that I put in myself... the stock ones were brighter in comparison. I took those ones out and put the stock ones back in and now all the preamp tubes glow at the same brightness level, but the squeal remains.

I then removed the FX loop send and return cables that I had hooked up to a delay pedal that I've been using lately. Less noise for sure, no more ground hum so that's good, but still the squeal remains.

Help?

 

[yngzaklynch]

One of your tubes is microphonic. My guess anyways.

 

[Tawlks]

Yeah, sounds like you have a microphonic pre. Grab a rubber hammer or a pencil/whatever and turn the amp on, take the back cover off and tap the preamp valves, you should hear a squeak, which ever valve makes the amp squeal when you hit it, that's the microphonic one.

My amp's fucked. Seriously.. I'd sell it if it wasn't hugely immoral to sell a broken amp. 5150s really aren't as reliable as people say they are.. I've heard a lot of horror stories.

 

[Ventura]

I'd sack all the glass in your V slots and just get back to basics... Go with whatever comes stock in the Peavey heads, probably Chinese A's or B's. They're cheap, and it's a blanket fix. Squeeling amps suck - as do many other things:

V.

 

[Laura]

The brightnesss of your pre's is probably not an issue. Mullard's for example, don't glow much in comparison to say Ruby's or JJ's...

Sounds like a bad tube but I would also clean all of your input jack and your effects loop jacks. A little dirt or a bad connection in your effects loop send/return jacks can cause problems with those amps.

 

[glpg80]

in 5150's they will not glow all the same brightness. this is intentional with the DC offset voltage of how james brown grouped the channels into the tubes and also the basis behind how a SLO works with one stage biased off.

you have a microphonic preamp tube.

 

[glpg80]

Sounds like a bad tube but I would also clean all of your input jack and your effects loop jacks. A little dirt or a bad connection in your effects loop send/return jacks can cause problems with those amps.

+1

 

[droptrd]

I hd this problem in a stiletto. Turned out to be a bad solder on a ground.

 

[JerryP]

Are you playing it without the preamp tube cover panel on? The glow doesn't tell you shit, Like Laura said they all glow different.
Jerry

 

[JakeAC5253]

Are you playing it without the preamp tube cover panel on? The glow doesn't tell you shit, Like Laura said they all glow different.
Jerry

Yes, well I have been playing with the cover off since I have been toying with different tubes.

 

[JerryP]

Are you playing it without the preamp tube cover panel on? The glow doesn't tell you shit, Like Laura said they all glow different.
Jerry

Yes, well I have been playing with the cover off since I have been toying with different tubes.

Put it back on and see what happens.
Jerry

 

[steve_k]

Are you playing it without the preamp tube cover panel on? The glow doesn't tell you shit, Like Laura said they all glow different.
Jerry

Yes, well I have been playing with the cover off since I have been toying with different tubes.

Put it back on and see what happens.
Jerry

That what them things are for Jer? Someone actually came on here the other day convincing people that an amp sounded better with them off. Believe that I will leave mine covered up on amps that were designed with them and leave the squealing to the pigs.

Steve

 

[Ventura]

Are you playing it without the preamp tube cover panel on? The glow doesn't tell you shit, Like Laura said they all glow different.
Jerry

Yes, well I have been playing with the cover off since I have been toying with different tubes.

Put it back on and see what happens.
Jerry

That what them things are for Jer? Someone actually came on here the other day convincing people that an amp sounded better with them off. Believe that I will leave mine covered up on amps that were designed with them and leave the squealing to the pigs.

Steve

This really proves to me that we have WAY too much time on our hands here at RT...

V.

 

[JakeAC5253]

I tried putting the preamp cover on and it didn't help. Then I tried swapping relatively new tubes all around the preamp and that didn't help either. What are the chances that the problem is in the power tubes?

 

[droptrd]

I know its a pain with the 5150s, but pull the board out and give it a full re-solder and see what happens.

 

[Ventura]

To psychodave's remark above...

I ain't IGNANT!!!!

What kinda backhand is that?!?! I was simply saying, considering there are masses of professional musicians out there who couldn't give a rats' ass about tube covers, cables or the like because they're too damn busy touring the globe and playing guitar, the fact that a bunch of monitor tanned freaks like us discussing the immense minutaie around such matters is baffling. We must have a lot of time on our hands!!

Bastid!!
V.

 

[kirk]

I tried putting the preamp cover on and it didn't help. Then I tried swapping relatively new tubes all around the preamp and that didn't help either. What are the chances that the problem is in the power tubes?

could be power tubes as well ,but what probably happened is ,the tube sockets are soldered to a pc board in that amp and are extremely subceptable to heat causeing solder joints to go bad and with you pushing and pulling new tubes in and out alot,has probably broken a joint lose causeing your headaches

 

[JerryP]

I tried putting the preamp cover on and it didn't help. Then I tried swapping relatively new tubes all around the preamp and that didn't help either. What are the chances that the problem is in the power tubes?

could be power tubes as well ,but what probably happened is ,the tube sockets are soldered to a pc board in that amp and are extremely subceptable to heat causeing solder joints to go bad and with you pushing and pulling new tubes in and out alot,has probably broken a joint lose causeing your headaches

Never seen an issue with a tube socket solder joint on a 5150 in all of them I've ever worked on. The power tubes are mounted above the sockets and since heat rises that's not ever going to be a problem on this amp. The preamp tubes are mounted sideways and they don't get hot enough so it's not an issue there either. A bad solder joint on a tube socket isn't going cause feedback.

If there were no issues before you started messing with tubes I suspect it's a tube issue. The 5150 will weed out bad tubes real fast with all the gain it has. The preamp tube cover must be installed as the foam acts as a damper to help prevent microphonics.
Jerry

 

[JakeAC5253]

Thanks for the advice everyone. I'll have to order a bunch of new tubes and see what that gets me.

Jerry, I sent you an email about a week ago, did you receive it?

 

[JerryP]

I'm way behind here, but I thought I've answered them all. I've been having some issues with my email account doing weird shit on me lately too.
Jerry