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Post by driventone on Mar 10, 2022 20:31:51 GMT -7
This is a weird one. I was doing some tube-rolling today, and I have a Siemens short-plate ECC83 that sounds good in V1 of one of my amps (a combo). When I went to put the tube shield on, every little movement came through the speaker, and I thought, “oh no, it’s super microphonic!” Even when I tap on the top of the amp, I can hear that through the speaker. Granted - the preamp was nearly cranked.
However, when I play through it, I don’t think I can hear any ringing or rattling or feedback of any kind. I’m playing at a fair volume, but not too loud. Maybe 90 db.
Would you notice a microphonic tube at that volume? Are there some microphonic tubes that aren’t really a problem, or they get worse over time?
I always thought that the “tap on the tube” test was how you can identify a microphonic tube, but as far as I can tell, it doesn’t have any unpleasant characteristics. Am I missing something?
If it is microphonic and starts to sound bad in V1, would it be ok in a cathode follower or phase inverter position? The triodes are nearly balanced (375/400).
Thank you!
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Post by perryr on Mar 10, 2022 21:52:50 GMT -7
If it sounds good it is good. A little micro isnt always bad, might even get a little extra sustain or add a little character that might be cool. I had a power tube in my Zwreck that was microphonic, not a rattle, but a lower frequency ring (uncommon), and boy would that amp sing with a fuzz pedal. Got to the point i needed to replace it and that howling sustain/feedback simmered right down (to my dismay).
I have some Siemens short plate (i62 code) and they are a ballsy tone with a nice edge, great 12ax7 and a great v1. If it becomes to micro for v1, it would be just fine anywhere else.
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Post by driventone on Mar 15, 2022 18:07:11 GMT -7
If it sounds good it is good. A little micro isnt always bad, might even get a little extra sustain or add a little character that might be cool. I'm glad you said this. From what I'm seeing, it seems like almost all preamp tubes may be microphonic to at least some degree, especially in V1 in a high-gain circuit. Just because I can hear a sound through the speaker when I tap on it, doesn't necessarily mean it's bad. The tube sounds good, so I left it there. Thanks Perry! I appreciate the input and the reassurance.
On a side note, I had a short-plate GE that I was told by a tech (when he tested it a few years ago) was high gain, but also microphonic. It sounds great in the phase inverter position!
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Post by helmi on Mar 20, 2022 5:18:57 GMT -7
Perry, won’t a triple mica tube tend to be more resistant and less microphonic?
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Post by perryr on Mar 20, 2022 9:22:20 GMT -7
Perry, won’t a triple mica tube tend to be more resistant and less microphonic? I dont know if the triple mice design was to reduce microphonics specifically, but it seems to be the case. Triple mica versions of 12ax7 and 5751 are often regarded as higher quality and less prone to microphonics. The few triple mica 12ax7 that i have (from the 60’s) are very nice and not microphonic.
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Post by zpilot on Apr 2, 2022 5:59:18 GMT -7
Back in the days before Russian and Chinese preamp tubes were the norm I used to prefer combos because of the way the vibrations from the speaker interacted with tubes. Domestic manufacturers tested their products for excessive microphonics. Current tubes can be a crap shoot in that regard. If I find a tube does not work well in a combo I segregate it into a stash I keep for using in heads. They usually work just fine there. Also they can be used in tremolo circuits no matter how micro they are.
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