Blues Jr. Amp Pop/Buzz

ragamuffin

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Hey guys, I know at least a few of you know your way around a tube amp. I've been experiencing a buzzy/farty sound coming from my amp when I play hard or on bassy notes. I tried replacing the power tubes and one of the preamp tubes, but I still get the same noise. I found that when I tap or slightly move the power tubes it makes the same noise. It's more of a loud, static-y "pop" than the snap noises it sounds like in the video.

Here's a vid of the buzz when playing, I have some delay on as it seems to accentuate it.
https://youtu.be/o_yyXRPSicQ

And here's a vid of me tapping/moving the power tubes
https://youtu.be/ccYpaWaTcrE

Any idea what could be wrong or if it might be a quick fix? Thanks guys.
 
Sadly your links don't work.

Would appreciate some pics so I can judge the age of the chassis, any mods, etc.

Some questions:

1 - does it make the sound with all the volume controls off?
2 - does it make the sound with the reverb off?
3 - if this is a master volume amp, does it do it with the master up and the gain off?  How about the reverse?
4 - Got a volt meter?

 
Mayfly said:
Sadly your links don't work.

Would appreciate some pics so I can judge the age of the chassis, any mods, etc.

Some questions:

1 - does it make the sound with all the volume controls off?
2 - does it make the sound with the reverb off?
3 - if this is a master volume amp, does it do it with the master up and the gain off?  How about the reverse?
4 - Got a volt meter?

I (think) I fixed the links

1-No sound unless I poke the power tubes, then it's just as loud as normal
2-Sound is there with reverb off
3-It does have master volume, no sound at all with it down or the gain down unless I poke the tubes
4-I do have a volt meter, but a very limited knowledge of how to use it

Thanks!
 
so, just for my understanding:

with all volume controls off,
Poke the power tubes,
makes the noise.

Is that right?
 
ok - I know what it is.  Your power amp tube sockets are loose and/or dirty and need cleaning, re-tensioning and/or replacing.

It's kinda tricky to explain, but essentially you

- turn the amp off
- discharge the caps
- remove the tubes
- clean up the pins of the tubes with some emery cloth
- straighten bent pins
- remove the chassis (so you can get at the sockets)
- with a metal probe re-tension each connector by gently prying the pinching faces of the contacts together.  If you're not comfortable with this kind of thing, don't do it.

I just realized that you've got EL84s in there.  Re-tensioning those 9 pin mini sockets is really hard.  If cleaning the pins does not fix it, you'll likely have to replace the sockets.
 
Mayfly said:
ok - I know what it is.  Your power amp tube sockets are loose and/or dirty and need cleaning, re-tensioning and/or replacing.

It's kinda tricky to explain, but essentially you

- turn the amp off
- discharge the caps
- remove the tubes
- clean up the pins of the tubes with some emery cloth
- straighten bent pins
- remove the chassis (so you can get at the sockets)
- with a metal probe re-tension each connector by gently prying the pinching faces of the contacts together.  If you're not comfortable with this kind of thing, don't do it.

I just realized that you've got EL84s in there.  Re-tensioning those 9 pin mini sockets is really hard.  If cleaning the pins does not fix it, you'll likely have to replace the sockets.

Thanks! I'll try cleaning the pins. Could I use compressed air or something to clean the sockets or is that just a waste of time? I may end up taking it to a tech, but at least now I can give them a better idea of what's going on.
 
given that you've already tried a new set of tubes, the problem likely is the sockets.  Compressed air likely won't do much for you.  Rather, you'd be better off with some contact cleaner in there.
 
Mayfly said:
given that you've already tried a new set of tubes, the problem likely is the sockets.  Compressed air likely won't do much for you.  Rather, you'd be better off with some contact cleaner in there.

Thanks! I'll get some tomorrow and give it a shot
 
make sure it's dry before you power it up again.

also, may as well check those sockets for arcing between the pins.
 
Just thought of something else:  This is likely a PCB amp.  If the sockets are soldered directly to the board the solder connections might have become loose over time.  May as well check that as well.

As always, pull the plug and discharge the caps before looking inside the chassis.
 
Tried spraying contact cleaner but unfortunately it didn't help

It is indeed a PCB amp, I'll try to check the connections, but I'm not completely sure what to look for
 
Here's the top and the sockets http://imgur.com/a/nkaDR

Can't really get a pic of the bottom of the board
 
Aha!  You've got cracked solder connections on what looks like each pin of that socket!  That'll do it.

If you've ever soldered guitar electronics you can fix this yourself:

1 - unplug the amp
2 - discharge the caps
3 - leave the tubes in there (they are keeping the sockets in place it seems)
4 - re-flow each pin connection with your iron and a little solder.  Put the iron on the pin and the pad.  Make sure the solder flows and the joint is shiny.  This should not take more than a couple of seconds per pad; If a pad starts to lift, stop.
5 - done.

Update - don't fry that ribbon cable.  Might want to unplug / relocate it while you're doing this.
Update Update - do both sockets.

and here's a pic for everyone else:

6XeVEdH.jpg
 
Mayfly's advice is good. He's got a good eye. Those joints are definitely problem children. But, I would handle it slightly differently to accomplish the same end, because that solder is clearly crystalized and won't reflow well. So, desolder the pins, then re-solder them. And don't use that PC board-destroying solder wick/braid/crap. That stuff is nothing but a cruel joke Satan plays on unsuspecting budding young techs. Use a solder sucker of some sort, preferably something along these lines...

17536.jpg

They're $5 at Digi-Key, and well worth the investment. They work much better because they're much faster, so you don't sit there with a 700° iron burning the traces off your PC board and carbonizing the resins in the fiberglass the board is made of. You simply arm the thing by depressing the plunger until it latches, melt the joint to get the solder fluid, place the tip at the joint and punch the button. It'll suck all that old, crystalized solder off the board in one swell foop. Then, you resolder with fresh solder, which gets you fresh flux in the bargain as well that'll clean the joint and help the solder flow. Leaving the old solder on there is just asking to have to do this all again in the near future.

Also, having a tool like that makes disassembling soldered electronic widgetry much easier should you ever need to be doing that.
 
It should unplug at either end.  From the picture the plug is buried on the other (inaccessible) side of the tube board, but I suspect you can just unplug it from the other board.
 
Mayfly said:
It should unplug at either end.  From the picture the plug is buried on the other (inaccessible) side of the tube board, but I suspect you can just unplug it from the other board.

Hmm, from what I can see it appears to be soldered at both sides...

This may be the proper time for a tactical retreat; I'm not really feeling comfortable that I won't mess something up with my soldering
 
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