random crakling sound on Fender red knob twin

[Helmholtz]

i can troubleshoot this with a wooden pencil or stick respecting the dangers of high voltages in this amp. Can you point out which plate resistor shall I be looking at?

Many possibilities. I would use freeze spray to localize the bad resistor.

Often the problem can be provoked by heating with an hairdryer and stopped with freeze spray.

[Jquijano]

Freeze spray with the amp on? Standby switch off?

[Helmholtz]

Freeze spray with the amp on? Standby switch off?

Amp fully activated, otherwise the problem (noise) can't show.

[Jquijano]

If you read this other forum, the users are describing the same frying bacon problem I am describing:

https://gearspace.com/board/geekzone...crackling.html

I would like to change all the amp stereo input jacks and then determine that it wasn't the problem.

[Helmholtz]

Have you tried a patch cord between preamp out and power amp in jacks?

Sometimes the switching jack contacts oxidate and can use some Deoxit cleaning.

[g1]

This amp does not have a straightforward tube layout. See pg.5 of attached for tube locations.

[Jquijano]

i did sprayed some deoxit d5 in a male jack and inserted and pull the jack from all the inputs of the amp. The crackling noise was reduced but its still present randomly.

[Jquijano]

Have you tried a patch cord between preamp out and power amp in jacks?

Sometimes the switching jack contacts oxidate and can use some Deoxit cleaning.

Well I sprayed deoxit D5 on a patch cable and gave it a good in and out yesterday. Today I have left the amp on, standby switch off and no crackling noise. Should I consider replacing those plastic mono and stereo jacks in the front and rear of the amp? Where else should i look at for any future frying bacon issue?

[Helmholtz]

Well I sprayed deoxit D5 on a patch cable and gave it a good in and out yesterday. Today I have left the amp on, standby switch off and no crackling noise. Should I consider replacing those plastic mono and stereo jacks in the front and rear of the amp?

I don't remember how those "plastic" jacks look.
Have you found a source for direct replacements?

I rarely need to replace a jack, but just spraying Deoxit might not be enough. I use Deoxit on a Q-tip and for the switching contacts I soak stripes of cardboard with Deoxit and push them between/pull them through the contacts.
In fact I avoid spraying Deoxit wherever possible.

Sometimes the contact tabs need to be re-bent/re-tensioned.

[g1]

If you google '9 pin fender jack' you will find them.
To me, it would be the 'power amp in' jack that would be the most likely suspect. You could temporarily jumper the switching pins to see if they are causing the issue.

[Jquijano]

If you google '9 pin fender jack' you will find them.
To me, it would be the 'power amp in' jack that would be the most likely suspect. You could temporarily jumper the switching pins to see if they are causing the issue.

How can you assume that the issue causing the crackling or frying bacon noise in the background attributes to a faulty power amp in Jack? What leads you to believe this is the target and not the other plastic jacks in the front, any pot or switch?

[Helmholtz]

If the probem stops with a patch cable between preamp out and power amp in, it's most likely the switching power amp in jack.
A patch cable bypasses that switch.
Not an unusual issue, but most often the signal cuts out completely due to oxidized switching contacts.

[g1]

How can you assume that the issue causing the crackling or frying bacon noise in the background attributes to a faulty power amp in Jack?

I suspected it because you said in post #23 that cleaning it got rid of the noise, at least temporarily.
The 'power amp in' jack has an internal switch that connects the preamp to the power amp. Like Helmholtz mentioned above, it often causes intermittent cut-out of the signal, but can also cause noise.
You can leave a patch cord connecting the 'pre-out' to the 'power amp in' to bypass the internal switch arrangement.

The 'frying bacon' sound you describe is not what I would expect from a bad PA IN jack, but your post #23 makes it seem suspect.