Whenever I tap anywhere on the amp it comes thru the speakers
 

Traynor Yba-200-2

I moved a pedal on top of my amp last nite, and I heard it thru the speakers. Thought, gee, that's weird. So I tapped the top with my finger and heard it through the speakers. Whenever I tap anywhere on the amp it comes thru the speakers. The taps are very light.

So I figured a microphonic preamp tube.

Changed all the preamp tubes - still there.

Had a friend who builds and fixes amps give it a quick listen. He tapped all over and heard the noise but said he never heard anything like it before. He can't get around to looking at it in earnest for a few days but I would like to if anyone hear has any ideas?

Thanks

Someone secretly planted a mic inside the amp? Seriously, that's odd though. I can't wait to read what the problem is/was.

A better description of the noise would be helpful. Sometimes it's a microphonic tube, sometimes it's a dirty or damaged socket, sometimes it's a dirty or damaged jack...

Microphonic power tube?

Yes it could be a microphonic power tube. Or it could be that one of your replacement tubes is also microphonic. At least these are the easiest things to check out.

If you think you have a microphonic tube use a single known good tube and go through and swap them one by one. Interesting issue though...

That's a 4-tube power stage, so in principle one could rotate through the power tubes running with only one on either phase to isolate a microphonic one. But have you cleaned all your sockets?

I had a ampeg amp that use to do that, it turn out to be a cold solder joint.
A faulty joint in electric wiring which results from the application of insufficient heat at the joint; the solder merely covers the joint and is not physically united with it.

Does it do that with the bass guitar unplugged?

With it fired up, go through and tap on each tube with the eraser end of a pencil. All may make a very slight noise, any that are louder than the rest are suspect.

did you try NOT tapping it?

That's about as funny as the clap.

Microphonic tube, bad/dirty jack or connector, bad solder joint. If you're careful and/or experienced with poking around in amps, you could try gently tapping components with something INSULATED (so NOT a pencil!) to identify the sensitive area or component.

+10000 don't kill yourself tube amps can be very dangerous even unplugged take it to a tech let them get your amp in top shape.

Pencils made from wood will work. Wood is a terrible material for conducting electricity.
So don't use metal pencils. :D

When working with tube amps, you must discharge the power suply caps before poking around in there. If you don't know how to do that, then take it to a tech.
A wooden pencil may have a conducting core and is not something I can recommend using for said activity.

If you can find a pencil with the graphite core also made of wood :)

I always used the butt end of a wooden spoon. Chopsticks work well, too. I'd say almost certain it's a microphonic tube. Solder joint might be possible but the tube is most likely IMHO.

Use a CHOPSTICK!

Wood or bamboo; not plastic, nor metal.

Maybe even wear a rubber glove to hold the chopstick...

Hey, stop that! Just 'cause I'm paranoid doesn't mean you have to laugh at me.

:hiding:

A chopstick recently dipped in chop suey could conduct 500V quite well....