Help with JCM800 Bass Series 1992

[Travis]

Hi everyone!

It makes this sound without any pedal or guitar connected.

Some recommendation?

issue(2).mp3

drive.google.com

https://drive.google.com/file/d/1147T6ck39eDy0_sVYTSBnaZ0Q55VFPg5/view?usp=sharing

 

[Travis]

The noise come and goes randomly

 

[Travis]

With a pencil I detect maybe the problem is V2 of preamp, I swap witht the other preamps tubes but the problem is always V2


It´s weird

 

[Travis]

I swap preamp tubes and the problem still there.


Some help please?

 

[Travis]

New preamp tubes and I clean sockets

 

[music6000]

New preamp tubes and I clean sockets

You are playing with some serious Volts in an Amp, It's not a 9V pedal.
No one here is going to give advice where to look in case you harm yourself.
You have done the Basic stuff, changing Preamp Tubes.
If that has not worked, Take it to a Amp Technician!

 

[Travis]

Without power tubes the noise dissapear.

I gonna try new EL34

 

[music6000]

Without power tubes the noise dissapear.

I gonna try new EL34

It may solve your issue but the Amp will need to be rebiased if you replace the Power tubes so unless you know how to do it, you still need to take it to an Amp Technician.

 

[Travis]

I could learn how to bias if It solved.

If not I Will ask a tech

 

[PJS]

Unless I seriously misunderstand what you are doing and how you are doing it then of course you are not going to get any noise out of the amp with the power tubes removed. You shouldn't get any sound of any type.

 

[Travis]

So, some recommendation about this noise usually comes from?

 

[Travis]

I know how to work with high voltage and guitar amps, but I´m not sure where to look with this noise.

That´s why I ask for some recommendation or if someone had similar experiences

 

[HamishR]

If it is an original JCM800 then it could be a few things. My first thought is obviously tubes - 99% of tube amp issues are tube related. But then a JCM800 could be up to 40 years old, so there are questions about the electrolytic caps and even ceramic caps.

First of all learn how to drain filter caps. If you don't want to learn that then take it to a tech. It could be a worn-out pot in the tone stack, an electrolytic cap or all sorts of things. It sounds tube-related to me and if you haven't replaced the EL34s in the last few years then that's my first guess. If the noise is specifically related to V2 it could be the treble cap which is probably ceramic and probably 250pF in that amp.

But it sounds like power tubes to me.