Retro STA Level Tubes gone microphonic

[Ben M]

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

[Sammas]

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?

[Ben M]

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