Impact 60 rev trem hum issue

[Leevi]

I have a hum issue with Impact 60 reverb tremolo. The preamp stages are identical if tremolo and reverb are disconnected from the circuit. I get a pretty loud hum (close to 50Hz) from the second channel even if tremolo and reverb are disconnected. If I remove the channel 2 preamp tube the hum drops to an acceptable level and channel 1 works fine. I cannot believe it is not a filtering issue since the voltage supply is common for both channels and channel 1 works alone fine. The hum does not increase with volume. Of course I have tried with several tubes and measured voltages which are ok.


/Leevi

[shooter]

I get a pretty loud hum

with NOTHING plugged in?

If I remove the channel 2 preamp tube the hum drops

I would check the input shorting jacks n the grounds in that area

[Leevi]

I get a pretty loud hum

with NOTHING plugged in?

If I remove the channel 2 preamp tube the hum drops

I would check the input shorting jacks n the grounds in that area

It hums nothing plugged in and on zero volume.
I recently changed the tube socked, no progress.


/Leevi

[Latole]

Any mods in the amp ?

Can you post pictures of wiring ?

Connect both positive input jacks  to ground ; hum or not ?

[Willabe]

Buzz/humm with nothing plugged in;

I would check the input shorting jacks n the grounds in that area

[Leevi]

The grounds are ok there.


Have attached a picture which is quite difficult to follow.
The most of the filter caps are located under the tag board.
There some small mods.


/Leevi

[Leevi]

I solved it with a workaround.
The noise comes from the reverb recovery and I wired the reverb pot in another way by swapping the wiper and lug 3.That reduces the noise if the reverb is not fully open.
I also biased the amp cooler which reduced the noise.
/Leevi

[Latole]

I also biased the amp cooler which reduced the noise.
/Leevi

Power tubes matched help to reduce noise.
Match don't need to be 100 % same.

15mfd bias filter, if bad, will induce hum. I'll put a 25 mfd