Turtlerock Forum

I've been hearing a noise coming from my Retro STA in the last couple of days so I decided to investigate. I had a concern that a tube had gone microphonic because of the noise I was hearing sounded similar to the sound you get. I did a tap test on the case and I hear the ping. I then wanted to find out which tube was making this happen. I did a tap test on each tube with the end of a pencil and they all do the same thing??
Hmmm

Is it possible for all of the 8 or so tubes to go microphonic all at the same time...or am I checking this incorrectly.

I'm thinking of emailing Phil Moore about this but wanted to touch base here first.

Bless your cotton socks T'rockers

Maaaarhhooorning Ben!
My experience with tubes in limited to only guitar amps, so take this for whatever it is worth.
Every tube will make a "ping" sound when it is tapped. A microphonic tube will have a sustained ring instead...
like this: http://www.tubedepot.com/microphonics.html


Is this the sound you are getting?

Thanks Nath and moornnning.

I've been having a closer look since I posted and have nailed it down to 1 tube (the 12AT7). It's got a slight sustain when I tap it and definitely seems to be the most reactive. The other 6 seem to be doing the normal tube sound thing.
I can see a small spike at 20khz on my spectrum analyser with the retro on (not that I can hear it) which may be coming from that 12AT7 as well.
Looks like I'll need to try another 12AT7 and see what floats.

Thanks for that.
Ben