Microphonic Driver Tube

I've heard of this but it's never happened to me until today. I was listening to Led Zep remastered through my VTA ST70 when between songs I thought I could hear a UFO landing! I paused my CD player and the sound faded. I hit play and paused it again, sitting much closer to the speaker, and sure enough there it was. By tapping on the left driver tube I could make the tube sing on its own. I was actually pretty excited (yes I've turned into a vacuum tube geek). To my disappointment it has stopped but I'm sure the tube is on its way out.

Pretty cool so I thought I'd share.

Kaner

kaner wrote:I've heard of this but it's never happened to me until today.  I was listening to Led Zep remastered through my VTA ST70 when between songs I thought I could hear a UFO landing!  I paused my CD player and the sound faded.  I hit play and paused it again, sitting much closer to the speaker, and sure enough there it was.  By tapping on the left driver tube I could make the tube sing on its own.  I was actually pretty excited (yes I've turned into a vacuum tube geek).  To my disappointment it has stopped but I'm sure the tube is on its way out.

Pretty cool so I thought I'd share.

Kaner

The tube may be just fine. ALL tubes are microphonic to some degree. If the tube made noise on it's own then it may well need replacement. But sometimes just tapping a tube will change things enough to allow the tube to continue to work well. Microphonics is not an indication of any other malady.

Some say old tube & ribbon Microphonics  the besr ever made............it the gift of useing tubes you are feeding back the sound of your room an your speakers in to the sound you hear...when using tube.........beit tube preamp an amps....
SS amps do not do this ever.....you can tap on you SS amp with a hamer...wont get much sound out of the speakers.....like none!
For me this is one reasion i like tubes.....an thay look cool.....an sound killer...
Got lov that feedback....



Thanks for the site Bob....................................

Ah ... well known issue. Playing Led Zepp on tube equipment can open a gate and summon Gozer the Destroyer. What you were hearing was his ringtone. Fortunately, that distracted him enough that he didn't come through.

Try playing the same track backwards and maybe you'll get lucky and summon Zuul instead:



Just be sure to cut the power before she mutates into a terror dog ... you really don't want that ...

* Microphonics is a circuit induced vibration of the internal elements of the tube. Those are of course attached to the pins, so you might get lucky and be able to damp the tube enough by tightening the socket some. As is, your problem may have "gone away" as the amp heated up due to expansion, or vice versa.

PS ... what kind of tube? Variety and make? The military versions got more beef to the internal structure and you shouldn't have the same problem ... look for the designator JW, JAN, Star, M, or W appended to the tube number ... I'm sure there's a slew of others I missed ...

Interesting acquisition here ...



Matched triplet of 12AU7A's. The star denotes military grade, and the tips are painted for tubes that test for low microphonics. Those are also graded by color and combination, and the red/yellow are supposed to be the uber best available from a production run. These would more than likely have been designated for something like ultra sensitive radar ... think DEW line back in the day.

Then again, that'd be easy enough to fake, so buy from a reputable dealer.

Not that "Singing" tubes has been a problem here ... I just got em because I thought they were neet, and I'm really liking Westinghouse. Running a triplet of 5963 Stars as we speak.