Weird noises Metro68 Plexi

[Derkoettner]

Hello
I have some Problems with my Metro 68 Plexi. When I Knock on the Ampchassis it make a drum noise (DOUING DOIUNG).
I changed the tubes. But still there was this noise. I think it comes from the metal. I cannot find out what it is.

Do you have any idea or expirience what this is?

Thanks

[Strat78]

A cold solder joint in the pre amp somewhere.

[Derkoettner]

So do I have to resolder all connections in the preampsection?

[neikeel]

So do I have to resolder all connections in the preampsection?

If the preamp tubes are not microphonic (you subbed these?) then that is likely diagnosis.

Go through the preamp each joint at a time and inspect first to make sure you have a mechanically sound joint, reheat and gently reflow each one in turn. When cool reinspect and dab with a red sharpie.

If you find a loose or dry joint you can stop and retry the amp but my suggestion is to start at V1 and go right through, including the tube sockets too. Take care not to add too much solder, you are reflowing - not just adding gobs of solder

[Derkoettner]

Hello

I heated up all the joints in the preampsection but still the same problem.
I have simply no idea what´s the cause for this . What is the red color on the joints? I have to replace it.

Do you have any idea what to do?

Thanks

[neikeel]

The red dye is quality control.

If itr is a Metro built one George may want to see it.

Where do you live?

[Derkoettner]

I live in Germany Nürnberg

Yes but where can i buy this color.

Its a metro.

[Derkoettner]

Ok I found the problem it was one of the inputjacks. Likely one of the contacts wasn`t closed. I put a cable in each jack and after that the noise was gone.

Thank you for your help

Mathias