20/20 strange high pitch noise when playing

[spikenet]

Hi,

my 20/20 has been geting a high pitch squeel for just a microsecond when you hit a chunky chord and mute it.

I'm guessing a tube is going microphonic but how do I test this? Would it be the 12AX7's or the EL84's?

thanks.

 

[disassembled]

Is it one channel or both?

Start swapping out the pre tubes out one at a time.

The EL84's are only supposed to be use for a year so if they are old I recommend replacing them.




Greg