Marshall JCM 800 2205 weird noise out of standby

[pontiacpete]

This making a very strange noise like a creaky squeaky door when when coming out of standby. I tried changing standby switch. That did nothing. Looks like the main filter caps are on the new side, F&Ts. Maybe this has something to do with negative feedback. Some had done so things to this. One of them is a 100k resistor in parallel to the 100k feedback resistor r33. Any ideas of what might be causing this?
Also is there another schematic for the 2205?

Marshall_jcm800_splitch_50w_2205.pdf

[Jon Snell]

I would check the EL34s bias voltage. If set too 'hot', it may be the screen grids moving as they heat up rapidly. Maybe it is a duff EL34 but as you state it is only as you apply HT to the amplifier, after checking for any rattling pf the EL34s, maybe leave it alone if there are no other symptoms.

[g1]

Also is there another schematic for the 2205?

Yes, the other version (attached) has transistor switching instead of IC.

[pontiacpete]

Forgot to mention, this is set up for 6550s

[Helmholtz]

One of them is a 100k resistor in parallel to the 100k feedback resistor r33.

This doubles the NFB signal which could give rise to oscillation with a low presence setting.
Turn up the presence fully and see.

If that doesn't make a difference I suspect a bad (arcing) standby switch.

[pontiacpete]

Anode to cathode,point 22 to 21, red lead on 22, 0vdc

[Helmholtz]

Anode to cathode,point 22 to 2, red lead on 22, 0vdc

Sorry, not clear.
Please just state the voltage from anode to cathode and if positive or negative.

Seems we both posted on the wrong thread, haha.

[pontiacpete]

Deleted

[Helmholtz]

Sorry I meant to write, measuring from point 22 to 21 it’s .005vdc.

This is the Marshall thread!