help diagnosing a pre-tube problem

[Triple Cheeseburger]

I have a problem on channel 3 which i am quite confident is pre-amp tube related. my gain in IV mode is set reasonably high (2:00) so i expect some level of noise, but its a little more than that. without an instrument plugged in, you can hear crackly noises, similar to a dodgy lead or something and some ground noise more so than usual. then when the channel volume reaches above 12:00 you can hear the tube becoming micro-phonic and squealing.

This is all fine, i have switched out pre-amp tubes before, until i open the manual and realize channel 3 has around 4 tubes driving it. alot more complicated than my old rectifier.

can anyone give me a rough idea of which tubes i should be trying? i sold my extra's when i sold my rectifier so ill have to buy a few tomorrow and play the switcharoo but if anyone can help me narrow it down that would be great.

 

[Triple Cheeseburger]

i will add:

this happens in all 3 modes in channel 3, and with any configuration of power setting, eq, bright etc.

channels 1 and 2 not affected at all. even when channel master at full

nothing plugged into amp input at the time.


i can still play it, however i assume it can only get worse.

 

[Barry]

start troubleshooting your preamp tubes (likely suspect) There is a tube layout in the manual that shows which ones effect channel 3 . Do you have a good spare 12ax7 ?

 

[Barry]

V 1 is a bit of a bugger to change but Thats where my problem was . V1 gets slammed harder than any other tube so you need a good one there . You might get one of the premium graded ones for that socket ?

 

[fuzzgod]

I noticed something similar on Ch3 (master cranked, bold on, gain hot) but only when the gEQ was active and I was running the 2200 (or highest frequencies) up too far. Had it checked out and it was just from pushing that much high frequency. Granted, I never play in those settings (not sure how I figured it out) but something to keep in mind perhaps.

 

[Triple Cheeseburger]

ok, similar but new problem.

when I play in band volumes on channels 2 and 3 i get un-usable squealing. when the gain is 12 oclock or higher ( i could understand if its maxed but i never take it above 3 oclock ) and you can hear it behind single notes and it kills my sustain.

i have gone through all pre-amp tube spots with new tubes, possible this is power tube related?