5150 problem

[tgs]

Alright, so the trusty old thing is behaving badly. If I turn the lead channel post gain past 3 it starts to sound like a mess. It's a stuttering sound, nothing musical, don't know how to better describe it.

The rhythm channel doesn't have this problem at all so I guess that rules out the power tubes? Does anyone have any idea what could be the problem? I don't know why these things always happen on fridays, hehe...

EDIT: I made a sample:
http://www.speedyshare.com/275702548.html

 

[Genius Gone Insane]

search...yes could be tubes...try contact cleaner on send/return...again, search

 

[TravisW]

If you have an extra 12ax7, try swapping out individual preamp tubes. I forgot which one is the first gain stage for the Lead channel, but that one is most likely your problem.

 

[tgs]

If you have an extra 12ax7, try swapping out individual preamp tubes. I forgot which one is the first gain stage for the Lead channel, but that one is most likely your problem.

I swapped the first one on the left and it seems to have done the trick. Thanks for the advice! Have to get another one though, just took some old tube I had laying around from changing in another preamp. Does it make sense to just change one tube or should I change all 5 of them?

 

[NickL]

Hose down every pot and jack on the unit with electrical contact cleaner. Works most of the time.

 

[Metaltastic]

"Hose" being a relative term

 

[GuitarHack]

In the 5150, all preamp tubes are used on the Rhythm and Lead Channel so it is a bit weird that you had a problem on the Lead channel only and changing the preamp tube fixed it. You said the tube on the left (I assume you are looking from the back) is the first gain stage of both channels. This tube is setup harder/hotter (to produce more gain) when the amp is on Lead, so maybe under the extra load it can't handle it. It is fine to just change 1 tube, no need to change them all.

 

[tgs]

In the 5150, all preamp tubes are used on the Rhythm and Lead Channel so it is a bit weird that you had a problem on the Lead channel only and changing the preamp tube fixed it. You said the tube on the left (I assume you are looking from the back) is the first gain stage of both channels. This tube is setup harder/hotter (to produce more gain) when the amp is on Lead, so maybe under the extra load it can't handle it. It is fine to just change 1 tube, no need to change them all.

Well, to be clear all I said was that I changed the tube on the left and the problem went away; it just happened to be the first tube I tried swapping and I still don't know if it was the first in the gain stage, hehe. I also have to run a more thorough test because it could also be that it starts messing up when it's hot.
But I also find it odd that only the lead channel is affected. It definitely seams to have something to do with the load since it's in direct relation to turning up the post gain. But hmm, now when I think about it I think the stutter went away when I turned the lead preamp gain down lower...

Oh well, another day, time for more analysis! If I have time. I'll probably hand it in to be serviced next week though, the tubes have been in a couple of years anyway. But I always think it's fun when you can fix something yourself.

EDIT: Nope, problem resurfaced, and eventually showed up on the rhythm channel as well. It seems to occur once it gets a bit warmer, and flipping it off for a while worked as a temporary solution just to get the tracking done for today.

 

[SuperD]

What The Broodwich said, seriously.
This is almost certainly a problem of dirt/corrosion in the FX loop jacks...promise, it's an easy fix...contact cleaner in all the jacks, plug a cord in a few times should get it up and running. Clean the pots and tube socket receptacles and pins at the same time .
And then thank The Broodwich...

 

[tgs]

What The Broodwich said, seriously.
This is almost certainly a problem of dirt/corrosion in the FX loop jacks...promise, it's an easy fix...contact cleaner in all the jacks, plug a cord in a few times should get it up and running. Clean the pots and tube socket receptacles and pins at the same time .
And then thank The Broodwich...

I did clean the FX loop. Didn't clean the pots because I didn't have time before we had to start tracking but I really wonder if that would be the problem here. But I'll give it a go! I want to retube it anyway so I'll take care of that on monday nevertheless. Cheers.

EDIT: Funny that I just noticed that I put up a clip with complete silence and nobody said a word.

 

[tgs]

Got the amp back from the service, including new amp tubes, bias switches, grounding cables and whatnot, hehe. Turned out the amp was "self oscillating", whatever that means. Either way, it's fixed! A much needed service, since it definitely sounds even better now.

Thanks for all your help! Too bad it wasn't something more simple.

 

[Metaltastic]

Hahaha, whatever that means indeed, I have no fucking clue! But hey, it works, and is as good as new, so that's all that matters!

 

[SuperD]

Glad to hear it's good to go!!! Thanks for checking back in, I was wondering how you made out.