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Tube Discussion Microphonics?

I have read in quite a few places where someone complained of this tube or that being microphonic. I understand what is meant in a discussion of matching output parameters but I have heard people say that a pair, or quad, of tubes were matched but still microphonic.

What does it mean for a tube to microphonic? How does this translate into audible identification? I mean how do you tell by listening whether a tube is microphonic or is just not a good sounding tube or not good sounding with a particular component?
motdathird
clueless
763 posts
 
Generally speaking, I can't agree with anything Sugarbrie said, but hey, that's audio.

Microphonics is not frequency dependant and it is the last way you want to adjust highs in a tube amp.

Tube amps without micrphonic tubes sound very good and generally better than those with them. If your tube amp sounds "dull" the last thing you want to look for is a microphonic tube to add to the mix. Change amps and use a different tube, change or tweak the circuit, make a better match with your speakers, blah, blah, blah... but I would not suggest shopping for microphonic tubes.

Sincerely,
I remain
eldartford
4,262 posts
 
Sugarbrie...OK...If fate gives you lemons, make lemonaid! Now please tell me why turntable rumble is a good thing.
karls
332 posts
 
I'm with the Clueless one here. Yikes, talk about an unpredictable tone control/ reverb pedal! Microphonics be bad, very bad!
motdathird OP
77 posts
 
I appreciate the responses and I will give my case in point. I recently bought a quad of 60's Telefunken 6922's for my linestage. They tested (16.0, 16.0), (15.5, 16.0), (16.0, 15.5), (15.0, 15.0). I had original Sovteks that sounded dry and did not have very good extension. I tried some Tesla that were so-so as far as extension but the midrange was like back in the next room.

I installed the Teles and the soundstage is great, midrange super, and highs brilliant and detailed (but not edgy). However, the low end, especially mid to low bass is really bloated. I had basically the same Teles in a linestage previously and the bass was very tight and controlled. So, I am wondering if this is a tube component mismatch or if it is a problem with one or more tube(s).

If any of the tubes were microphonic, would I have audible problems throughout the range or could it be frequency-specific?
sugarbrie
3,854 posts
 
If the tube is only slightly microphonic when you tap on it, then what is the problem? I agree 100% that a tube that is microphonic in normal use is a piece of junk.

Folks including Kevin Deal at Upscale Audio, who sells some of the best NOS tubes, has said similar things.

http://www.duncanamps.com/technical/microphonic.html

If all distortion is bad, then why do they add white noise on purpose in CD playback?
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