Marshall jvm410 Rustleing paper sound until warmed up.

[Captain chunkulus]

Okay so I have this Marshall jvm410 head. As the title reads, has rustling paper like sound upon startup. Power It Up and let it sit for a little while and no matter how long I let it sit before I take it off standby it does the same thing. the wrestling paper sound for a little while. Seems to go with the bias. As the bias increases as the amp is warming up, the rustling paper sound is in effect so to speak. I bought this amp second-hand and it appears that someone modded the bias circuit. The values are the same in regards to the resisters. They changed out the pots for the bias circuit. I'm guessing so they coud bias the amp for something other than el34s. I'm not really sure. Any ideas on what might be causing the rustling paper sound. I goes away after a while. I've changed out all the power tubes and all the preamp tubes with brand new tubes does exactly the same thing regardless of what tubes are in it. Thanks guys.

[Latole]

".. the wrestling paper sound for a little while. Seems to go with the bias."

-Captain chunkulus,


Like a SHRHRHRHH ?

Is the bias is the good one ?

Or it is a bad solder in power supply ?

 

[Latole]

Or stanby switch arcing ?

[Captain chunkulus]

How would I determine standby switch arching?

[Latole]

How would I determine standby switch arching?

IMO reading ohms with a meeter may show some resistor at stanby switch contacts.
You should disconnect all wire from the switch.


Discharge filter caps before, lethal voltage ; amp disconnected from the wall outlet, power ON and stanby switch to Play, wait half hour or less if you can read voltage at filter caps to see voltage drop close to few volts or 0

[pdf64]

How about if you power up without a tube in the V5 phase splitter socket?

[Captain chunkulus]

How about if you power up without a tube in the V5 phase splitter socket?

No sound at all with the phase splitter pulled.

[Latole]

"Any ideas on what might be causing the rustling paper sound. I goes away after a while."
- Captain Chunkulus

I wonder if it wouldn't be a signal cap that would have a momentary DC leak ?

[pdf64]

No sound at all with the phase splitter pulled.

How about if a shorted jack plug is plugged into the PA in return jack? Could use a lead with a guitar whose vol controls were turned to minimum.
If no noise, how about the same with the fx loop return jack?