Strange speaker thump?

[brewdude]

This weekend I was playing my D'Lite and noticed that my amp has picked up a strange speaker thump which seems to be independent of the signal. It sounds a little like a well muffled kick drum. It happens randomly with out any regular time intervals. Clean or OD, I can't seem to find a way to intentionally induce it. It even happens when I set the guitar down.

I was wondering if there was a strange signal interference that could contribute to it. My old house's wiring is not quite up to current codes. So, I thought it might exhibit this behavior using the same speaker with a different amp, but no.

Before I start pulling my hair out trying to ignorantly diagnose my problem, does anybody have a suggestion as to what might cause this issue? Tubes? Caps? Transformer?

[ayan]

This weekend I was playing my D'Lite and noticed that my amp has picked up a strange speaker thump which seems to be independent of the signal. It sounds a little like a well muffled kick drum. It happens randomly with out any regular time intervals. Clean or OD, I can't seem to find a way to intentionally induce it. It even happens when I set the guitar down.

I was wondering if there was a strange signal interference that could contribute to it. My old house's wiring is not quite up to current codes. So, I thought it might exhibit this behavior using the same speaker with a different amp, but no.

Before I start pulling my hair out trying to ignorantly diagnose my problem, does anybody have a suggestion as to what might cause this issue? Tubes? Caps? Transformer?

Could you power tubes be going south?

G.

[brewdude]

Thanks for the reply.

I hope not. They are only about a month old. They seem to sound fine. Except for the weird sporadic random speaker noise, it sounds pretty good.

I could swap them for the old pair. The reason I replaced the original pair (JJ 6V6's) was that one of them seemed to experience an acute upward drift in bias current.

[67plexi]

Make sure you don’t have a cold solder joint on the primary side output transformer pin #3. A spark will cause the symptom you are having.

[brewdude]

So... I started thinking, and decided to check the bias. Both tubes seem to have higher current than I remember, but one had drifted way up. I set them at 18.35mV and 19.65mV, but they were more like 19.65mV and 24.5mV.

I swapped sockets with the same pair and fired it back up. Now, they are set at 18.85mV and 18.25mV.

So far,no speaker popping. I will keep my fingers crossed and hope its fixed and all is well, but I suspect there is a reason things got weird and I will keep a close eye on it.

[Bob-I]

So... I started thinking, and decided to check the bias. Both tubes seem to have higher current than I remember, but one had drifted way up. I set them at 18.35mV and 19.65mV, but they were more like 19.65mV and 24.5mV.

I swapped sockets with the same pair and fired it back up. Now, they are set at 18.85mV and 18.25mV.

So far,no speaker popping. I will keep my fingers crossed and hope its fixed and all is well, but I suspect there is a reason things got weird and I will keep a close eye on it.

Sounds to me like a loose or dirty pin on one of the output tubes. I'd clean and re-tension the tube sockets.

[brewdude]

Man, this is frustrating. I just came back to re-check the bias and now it's too low and the tubes are further apart in current draw then last time.

So I reset the bias again, with the lower value set at ~18.0mV and the other at 19.5mV. I suspect that my AC line voltage is fluctuating drastically. Could there be a flaw in the circuit that would make it do this?

[brewdude]

Sounds to me like a loose or dirty pin on one of the output tubes. I'd clean and re-tension the tube sockets.

How do I re-tension the tube sockets?

[Bob-I]

Sounds to me like a loose or dirty pin on one of the output tubes. I'd clean and re-tension the tube sockets.

How do I re-tension the tube sockets?

Tube sockets have little clamps that grab the tube pins. Take a tiny poker, like a dentist's pick and push the clamps so that they'll grip the tube pins tighter. Also clean the socket by putting alcohol on the tube pins and sliding them in and out.

[brewdude]

Sounds to me like a loose or dirty pin on one of the output tubes. I'd clean and re-tension the tube sockets.

How do I re-tension the tube sockets?

Tube sockets have little clamps that grab the tube pins. Take a tiny poker, like a dentist's pick and push the clamps so that they'll grip the tube pins tighter. Also clean the socket by putting alcohol on the tube pins and sliding them in and out.

Thanks, I'll give it a try.