volume knob crackling (not what you think)

[bleachedfan]

Ok so my volume knob on the rhythm channel (mesa maverick) crackled. I switched it with a different knob..still crackles. I switched it with the bass pot from the lead channel (bases on the manual its the same pot). What would cause the different pot to crackle? I believe this is the cause of my hum problem. Also, if I tap on the vol pot, I can hear it through the speakers. Soo confused.

 

[TheMichaelAbe]

this is really interesting actually...I hope that someone with way more technical knowledge than I have can help you out! I'll be on the lookout for answers

 

[piggyboy]

i would try swapping the pre amp valves I think its v1 or v2 thats most likely a problem.
have you tried tapping them with your fingernail/end of a pencil test?
check the el84s too

 

[bendo]

i would try swapping the pre amp valves I think its v1 or v2 thats most likely a problem.
have you tried tapping them with your fingernail/end of a pencil test?
check the el84s too

+1 a faulty failing tube can crackle when more power is added (turning up the output/gain).

 

[bleachedfan]

How do I check the el84s? Can they become microphonic as well? What do I look for?

 

[piggyboy]

How do I check the el84s?

with the amp on - just give each of them a light tap with your fingernail or the end of a pencil, if theyre microphonic you'll hear it from the speaker.

 

[bleachedfan]

I never knew power tubes could go microphonic. I thought they would just blow.

 

[MrMarkIII]

Crackling and microphonic are two different problems, one is a knob, the other a tube.
The crackling when you twiddle your knob is usually caused by the high gain circuit the knob is controlling. I cannot imagine this being a problem unless you stand in front of the amp and twist the poor thing back and forth while playing.
Tubes exhibit microphonics when the tube is vibrated by the loud sounds coming from the speaker, causing the internal workings of the tube to vibrate sympathetically. This is feedback. It gets worse the more the volume is increased by that crackling knob, and if you thump the tube, thus making the familiar squealing noise. EL-84 tubes are more prone to microphonics than others because they're small and skinny and have less mass, so they can get to shaking easily.