Low microphonics preamp tubes

[mashaffer]

In my experience 12AX7 has a tendency to microphonics and the 12AY7 is pretty resistant to it. What I would like to see is a listing of tubes that tend to be resistant to microphonics. It seems to be a a hard thing to quantify but important in some applications.

 

[turk 182]

is it the tube or the circuit? the 12ax7 as a preamp tube is driven at ridiculous high gain levels and max heater voltages in an effort to squeeze more out of it, which shortens life (especially in instrument pre-amps) the 12ay7 is lower in gain to begin with.
i say look at how it's being used before you jump to a conclusion the tube type has a "tendancy" to microphonics.

 

[Merlinb]

12AX7 is not generally a microphonic tube. Sometimes you get an unlucky sample, but that is true for anything.

Frame grid tubes like the ECC88, and tubes where the getter is supported by a single wire, tend to be more sensitive to microphonics.

 

[Lingwendil]

Most of the Russian "EV" types are pretty nice tubes that aren't very microphonic. The best 12AX7 you can get is actually the 6N2P 🙂

 

[piano3]

My experience is that it is often the very high gm pentodes which are microphonic. Try 6s17k for zero microphonics.

 

[Wavebourn]

My experience is that it is often the very high gm pentodes which are microphonic. Try 6s17k for zero microphonics.

6S17K is zero microphonic, but it can't substitute 12AX7 because it's grid is too close to cathode, it's grid current is much higher. I use them with grounded cathode, and bias by 47k and it's own grid current. Excellent for new design in phono and microphone preamps, but can't replace 12AX7.

 

[hego]

Most of the Russian "EV" types are pretty nice tubes that aren't very microphonic. The best 12AX7 you can get is actually the 6N2P 🙂

I agree !!!

The 6n2p-eb is very quiet. I use them in my phono-pre.

Others I tried, in especial new chinesse (MkII) with frame-grid tech, are like a bells.Horribles!!!

Cheers

 

[tiefbassuebertr]

I am not sure, but I think it is possible that the most suitable tube for low microphonics should also be selected in order to the used circuit topology.
Currently I have a diy-preamp based of Thorsten Loesch' Shindo Claret for remove unwanted microphonic effects in the line stage - the circuit diagram and description of which can be found under
https://community.fortunecity.ws/rivendell/xentar/1179/projects/claret/Claret.html
The line stage has an extremely strong microphonic effect since several weeks, which remains unchanged even when the volume control is adjust to zero. Maybe due an aging effect of the ECC81/12AT7, but possibly additionally enhanced by Shindo's circuit topology (please note: the attenuator changed also the feedback factor due the fact, that the grid resistor don't goes to GND).

The question is, what is the best suited tube type and brand for this circuit topology ?
An other question is, whether there is a possibility to modify the circuit in such a way, that the microphonic effects is reduced.
Best thanks in advance.

P.S.: Until now I know such large microphonic effects only on MM-RIAA stages without connected ton arm cable (open input) and without or very high impedance load resistor. In this case this effect is usual and is strongly reduced by connected the ton arm cable to the phono input (input impedance was now determined by the cartridge coils).

P.S-II.: URL from post #3 under

B

Thread 'Why do valves go microphonic?'

2008-09-24 1:43 pm

My phono preamp (self-built) has as its input valve a triode-connected D3a. It has been playing quite happily for months but yesterday the right-hand channel went microphonic contributing its own monotonic drone to the music. Nothing I did to decouple the preamp chassis from its environment had any effect, but substituting a fresh D3a did the trick. Now the D3a is a high-gain (mu = 70), high gm (40ma/V) triode, but I am currently playing Berlioz's Damnation de Faust at a satisfying volume-level without any microphonics at all. Is it something to do with the frame-grid distorting, or what?

• barretter
• Replies: 7
• Forum: Tubes / Valves

is dead, but available here (pg. 48-50):
https://web.archive.org/web/2007102...1960_Getting_the_Most_Out_of_Vacuum_Tubes.pdf
and in the attached file.
More URL's to this topic
https://www.diyaudio.com/community/threads/tubes-microphonic.328490/ (test procedure therefore)
https://gearspace.com/board/so-many-guitars-so-little-time/1372993-microphony-tube-amps.html

 

[tiefbassuebertr]

Thorsten Loesch' Shindo Claret works fine in the line stage - i. e. now without significant microphonics effects after replace the tubes by the Philips version GB6201 - go to
https://www.ebay.de/itm/226341509703
and
https://www.tubeampdoctor.com/gb-6201-12at7wa-philips-ecg-gold-brand-nos-nib
some offers of this tubes are very expensive like that:
https://www.ebay.com/itm/266904373984

P.S.: the previous tubes with significant unwanted microphonics effects are usual ECC81 (Philips MINIWATT).

 

[hooman]

Most of the Russian "EV" types are pretty nice tubes that aren't very microphonic. The best 12AX7 you can get is actually the 6N2P 🙂

The tubes used in the pre-amp must have a good sound in the first place. Cheap Russian tubes cannot be suitable. I made all-tubes pre- amp based on the orders of demanding customers. I had to use the best.

 

[EC8010]

Frame grid valves should be less microphonic but can become microphonic if they develop RF oscillation. The cure is grid stoppers and good RF decoupling to prevent the oscillation, at which point the microphony will go away as well.

 

[hooman]

ecc83-12ax7 it works in the guitar amplifier at high gain and there is no microphonic. Suggesting to use frame grid! It is not necessary ....... just use good brand ecc83. Do these materials really teach beginners?