Delta Blues gets periodically louder

[inselwissen]

Hi there,

I bought a used Delta Blues 1x15" combo a few weeks ago and it has a problem that is driving me nuts.

When playing for longer than a few minutes, the amp gets louder for like half a minute, then returns to "normal" volume. It's like bumping up the volume knob half a number. I get a bit more white noise, a bit more hum, but no added distortion or anything like that. Both channels behave that way.

I just did a full tube swap (Classic30inCincy's PAF set) and I've tried various spare tubes in all positions. I'm going straight into the amp for testing purposes, Reverb off. I also tried "patching" the effects loop and it didn't help. It's definitely not my guitar cables or stomp boxes either as I can hear the problem even when nothing is plugged in: There's 20-30 of increased noise, then it's back to normal.

Do you guys have some more ideas for me? The amp itself sounds great and I'd like to avoid having to pay for a tech.

Greetings from Germany!

[G.W. Hayduke]

Interesting problem. How long do you warm the tubes up on standby before playing?

[Enzo]

Keep the reverb off so the springs don't crash, ball up your fist, and whack the top of the amp hard while it runs. Does it react? Does it affect this issue? This helps expose loose connections.

Inside, the boards are in three sections, linked together by rows of many short bare wire jumpers. Those sometimes crack and break free. Also a couple of them sometimes overheat and the solder fails.

[KTB]

Did you do power tube swaps or preamp tube swaps. The power tubes are the ones that cause volume swell and also connect a cable from the send to return jack and see if it stops.

[inselwissen]

Did you do power tube swaps or preamp tube swaps. The power tubes are the ones that cause volume swell and also connect a cable from the send to return jack and see if it stops.

I swapped out all of the tubes. I bought a matched set of JJ EL84s, a Tung Sol 12AX7 for V1, a JJ ECC803s for V2 (massive improvement, took the fizz right out) and a Sovtek 12AX7LPS for V3. Huge tonal improvements, no effect on my problem.

Keep the reverb off so the springs don't crash, ball up your fist, and whack the top of the amp hard while it runs. Does it react? Does it affect this issue? This helps expose loose connections.

Inside, the boards are in three sections, linked together by rows of many short bare wire jumpers. Those sometimes crack and break free. Also a couple of them sometimes overheat and the solder fails.

Whacking the amp doesn't change anything, unfortunately.

I made some progress either way. Bought some contact cleaner and cleaned the pots, which was long overdue. Couldn't quite get the reverb pot and the two drive volumes to stop crackling, but now the EQ pots and the clean volume pot are totally quiet. Which is all I really need, because I bought the DB to use as a pedal platform.

I also cleaned the tube sockets using interdental brushes dipped in contact cleaner. And guess what.. It's better now!
When I turned on the amp for the first time after cleaning the sockets it first went to the lower volume and then got louder after two minutes of playing. That was a few hours ago. I left the amp on next to me while I did some work and the volume didn't noticeably change during all that time. So I guess the problem has at least been mitigated a bit.

As for next steps, I'm thinking of lugging the amp to band practice later this week. In a band mix I'll know right away if and when the volume changes. Also, transporting the thing to our practice space should make for a good road test. I'll report back after practice.

Thanks so far guys, if you have any suggestions, don't hesitate to post. I don't know if I'm over the hill yet.

[bigboyneverleft]

Well I seem to be in the same boat. After years of joy I get volume to spike from time to time.
I removed all pedals from FX loop to the front. Then removed all pedals and it still happened. Tried to clean all pots, but the real way to do it is impossible without disassembly.

I do suffer from lots of "storm" noise when it warms up and of course it was not the case some years back.
Looking into more options.

Inselwissen, did you ever find the issue?

[Pappy B]

Sounds like a thermal issue. It is probably time to look for bad solder joints.

My Classic VT started making a ticking noise as it warmed up. I found a questionable solder joint on a tube socket. I reflowed the solder on both sockets and is is very quiet as it warms up now. Like it should be.