Intermittent bacon sizzle

[nandrewjackson]

The amp is a modded 65 princeton reverb reissue.


It still has PC boards. The mods are LED at tremolo oscillator cathode, NFB 3 way switch, mid resistor and "raw" switch in EQ, added 300K grid stopper @ P.I.


When the amp is sitting idle, there is some audible bacon sizzle sound for a few seconds, every 20 minutes or so.


It happens with and without anything plugged into the input jack.
It is audible with volume all the way down, BUT, it gets louder with volume level turned up.


I've had luck getting rid of intermittent bacon sizzle sound on other amps by changing preamp tube anode resistors to metal film / metal oxide.
BUT, the couple times I've had that chassis out, I noticed, based on their appearance,  the preamp anode resistors appear to already be metal film/ metal oxide types.


Since the bacon sizzle sound gets louder with volume up, I'm thinking its the 1st triode anode resistor.


I've also had luck getting rid of intermittent bacon sizzle sound by changing pots.


Any thoughts?
Thanks in advance.

[stratomaster]

A few seconds every 20 min or so sounds like a power line issue to me.  Could be something else on the circuit cycling. Is a refrigerator or freezer on the same circuit?

Failing that, you can use targeted heat to attempt to force the failure, just don't induce damage in the process of testing.

[acheld]

Ribbon cable connections?    Cold solder?

Intermittent just sucks.