Microphonic issue with 15 differents preamp tubes, could be?

  • Thread starter Thread starter adrianher
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adrianher

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I have some Cameron's marshall mod. Last gig a stupid guy came to the stage and touching the amp he made it fall.
The amp works but it has some additional floor noise and a background groundloop. It has lot of microphonic hitting the chasis, and a lot more tapping v1 with a pencil (v2 and v3 are quiet, also power tubes when I tap them).

I've tried 15 differents preamp tubes that I had stocked some years ago. Cold be that the 15 tubes had gone microphonic tubes??

Anyone can suggest me what to do?? Or if there is any other issue besides the v1 tube?

Thanks
Adrian
 
Its doubtful that all 15 preamp tubes are microphonic. Could just need to retentsion the v1 tube socket or could have something loose inside the amp.

Also try swapping v2 into v1 and see what happens.
 
I would imagine that the fall caused this issue. Only option is to take it to a tech that MIGHT be able to diagnose it, or maybe send it out to Friedman who has worked with Mark's circuits a bit. Good luck! Or Mark himself, some guys on the board keep in touch with him. Maybe they can chime in?
 
Thank for inputs. The only tech around here doesn't want to touch it since is gooped and moded. I've send a FBk message to Mark since we had contact some years ago (I bought my 3 amps direct from him) but no answer at all. To send to some tech is possible since in Argentina importation is closed, I'll be able to send it but not to receive t back!

Thanks
 
If you are not comfortable opening the amp up and poking around while it is powered up to locate an issue you are basically sol if you don't have someone that can. It sounds like something came loose from the fall and I would start at the input and first gain stage. I would also check y=the power tubes since they are more than likely to suffer from a fall than the preamp tubes.
 
I've opened both amps and resolder each amp point (on the exception of the ones that mark had gooped) it works flawessly again, both are hi gain amps (Jose and Aldrich) but I still hear that metallic sound when I tap v1. Tomorrow with more time I'll test again the preamp tubes and let you know.

Thanks
 
It's totally possible for 15 preamp tubes to be microphonic in the first high gain slot. It's just to what degree. Best for low microphonics is jj tubes, I use these in the first slot. It is also possible for power tubes to be microphonic, if so they are shot.
 
adrianher":1ns4mbz4 said:
I've opened both amps and resolder each amp point (on the exception of the ones that mark had gooped) it works flawessly again, both are hi gain amps (Jose and Aldrich) but I still hear that metallic sound when I tap v1. Tomorrow with more time I'll test again the preamp tubes and let you know.

Thanks
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Like Dave said. That's normal
 
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