Intermittent fart-like crackling noise; Ch1 & 2. Any Ideas?

[Catthan]

Hey guys,
what do you think?
I get farty cracking noise in channels 1 and 2. 90W, loop in, preset eq, all modes.

Ch3 is fine so far.

I'm looking at the manual to see which pre- tube affects Ch.1 & 2 and not 3 and I'm getting a bit confused..
Actually the fact that Ch3 is fine worries me a bit that it's smth other than a tube..

Anyhoo, I'll check the tubes and try a new one in V1 to V3.
In the meantime I would appreciate some input..

Best,

 

[elvis]

Phase inverter can do that.

 

[Catthan]

^^^
Thank you Elvis,
Wouldn't PI affect all 3 channels tho?

 

[Catthan]

swapped V1-3 and the PI to no avail..
off to the tech?

As this happens in ch.1&2 I have ruled out the power stage.
no arcing, strange glows, volume loss or smoke either..
anyone knows what do ch.1&2 share other than preamp tubes?

 

[jb's 52]

Does this happen in all wattage settings?

Crackling, I found, is a usually a pre-amp tube.
Try deactivating the loop, I found it easier to pinpoint
microphonic tubes that way.

 

[Catthan]

Does this happen in all wattage settings?

Crackling, I found, is a usually a pre-amp tube.
Try deactivating the loop, I found it easier to pinpoint
microphonic tubes that way.

Thank you jb's 52,
I pulled the chassis and think I located the issue to the loop tube.
Most likely smth with the contacts. Applied contact cleaner and so far it's been quiet.
I didn't change wattage, kept all at 90W.
Haven't given it a proper playthrough yet 'cause the neighbor underneath bangs the floor (his ceiling) but I leave it on and it's quiet so far.

 

[steve_k]

Does this happen in all wattage settings?

Crackling, I found, is a usually a pre-amp tube.
Try deactivating the loop, I found it easier to pinpoint
microphonic tubes that way.

Thank you jb's 52,
I pulled the chassis and think I located the issue to the loop tube.
Most likely smth with the contacts. Applied contact cleaner and so far it's been quiet.
I didn't change wattage, kept all at 90W.
Haven't given it a proper playthrough yet 'cause the neighbor underneath bangs the floor (his ceiling) but I leave it on and it's quiet so far.

Did you get this resolved? I bought a back up Mark V to run two of them in my rig and it was supposedly new, but I am thinking it was a demo that someone jacked around with and damaged it. It's going back, but here's what I think. Like yours, channel 3 is fine, and the loop works fine on it too. It is mostly like a result of someone flipping channel 1 and 2 onto the lower watt modes while on the high power setting and frying something in the rectifier/diode circuitry. Symptoms of mine is low output on channel 1 and very little gain on channel 2. Removed the chassis and rolled a number of tubes in it to no avail. I know when they MkV first came out, there were warnings of not to engage certain settings in high power.

 

[Catthan]

Did you get this resolved? I bought a back up Mark V to run two of them in my rig and it was supposedly new, but I am thinking it was a demo that someone jacked around with and damaged it. It's going back, but here's what I think. Like yours, channel 3 is fine, and the loop works fine on it too. It is mostly like a result of someone flipping channel 1 and 2 onto the lower watt modes while on the high power setting and frying something in the rectifier/diode circuitry. Symptoms of mine is low output on channel 1 and very little gain on channel 2. Removed the chassis and rolled a number of tubes in it to no avail. I know when they MkV first came out, there were warnings of not to engage certain settings in high power.

Hey Steve. I think mine is OK so far. Contact cleaner in the loop tube did the job.
I didn't get any volume loss though..