Peavey C30 squeals

[pulsar705]

With the following setup
PRE = 6/7 ; POST=6/7 and MASTER = 9/10

i feel a little squeal/feedback that happens even if the guitar is not connected. Any suggestions?

thanks, jon

[oc disorder]

One of the pre-amp valves has gone microphonic.
This means the internal mechanical structure can vibrate
and act like a microphone.Thus when close to a speaker it can feed back.
This seems more common in combos where the speaker can rattle the s&%t out of them!
Try tapping them lightly with a biro to find the main offender.
Just a matter of fitting a new one.
You could try as a temporary measure swapping them round
as they are all 12AX7's.
The microphonic one may still work ok in a less sensitive position.
Unfortunatly even new ones can be microphonic these days.
One of the JJ's is supposed to be low microphony, the ECC83S.
some info here on 12AX7's
http://www.guitaramplifierblueprinting.com/12ax7.html
The TungSol 12AX7 is supposed to also be low microphony although
I have not tried them.
" TungSol 12AX7 has small plate design with star micas that are well supported in the glass. This makes it low in microphony and TungSol 12AX7 is suitable for use in phono stages."
So its suitable for Hi-Fi use but you will have to check user forums to see how it performs in a guitar amp.

[pulsar705]

One of the pre-amp valves has gone microphonic.

i replaced the pre-tubes and i fixed,but I have not done heating tubes. I hope that remains ok.

thanks,jon