Tube Amp Problem

[sammol]

I have an old amplifier that farts, more on lower frequencies.

The speaker is ok. I've cleaned the potentiometers with a contact cleaner but the flabby tone is still there.

Here's a soundclip recorded with shure sm57:
farting tube amp soundclip by kalabian on SoundCloud - Create, record and share your sounds for free

Do the tubes need to be replaced?
It's a boutique amp btw.

 

[miroslav]

What makes you think the speaker is OK...how did you check/test that?

You can of course swap out the tubes, as they might need to be swapped anyway if it is an older amp...but I don't think that's a tube problem.

 

[ocnor]

Maybe you should just sell the amp to Neil Young.

 

[drumslinger]

Hay sammol,

- tubes? maybe. when was the last time they were changed out?
- i know you checked the speaker but see if you can find any small rips? just double check it.
- when was the last time the tubes were biased? this could be another issue with the amp farting.
- you see any red plating on the output tubes when playing the amp?
- could also be a leaking coupling cap in the amp.
- what's the bass pot set at?
- have you tried an external speaker to see if you get the same result?
- does the amp have a tube rectifier? these tubes can sometimes be the culprit.
- have you tried swapping preamp tubes as well?

 

[sammol]

I'll just bring it to a shop.

anyway before I do that, here's another problem, a tube is popping.
Tube Amp popping - YouTube

 

[sammol]

I'll just bring it to a shop.

anyway before I do that, here's another problem, a tube is popping.
Tube Amp popping - YouTube

 

[ranjam]

Take it to a shop. It is an old Fender by the look of the chassis (or what little I can see), so anyone who knows what end of a soldering iron to hold should have it fixed in an hour or two. The one tube that is 'flashing' is bad, and like caused by age, but possibly a leaky coupling capacitor, which can also cause the farting.
The farting is either the bias is much too high, one 6L6 is idling much lower than the other, or that bad coupling capacitor. But you are still better off taking the amp to someone who can have it singing like it ought to rather than risking a shocking discovery that you really aren't cut out to be an amp tech.

 

[Blue Jinn]

OT: I stuck two tubes in a 6L6 amp, based solely on the same pinout! I think they were 6V6 and 6H6. Can't remember. One was gassy as well, and when you turned up the bass, the gas would pulsate and it would make this odd tremolo like effect (whump whump whump). But it actually made a (distorted) sound that was actually usable. Crazy thing how much tolerance tube circuits have. That was some serious abuse....

I still have that amp, (it was a MonkeyWards house brand!) and I plan to actually restore the thing.