Pre-amp dual triode microphonics vs. physical size?

[RickH]

Are larger GT tubes (in mass sampling) less microphonic than 9 pin
tubes used in preamp and phase inverter stages?

Specifically I'd like to know if 6SL7GT (or a 6SN7GT), both large GT
tubes, would over a large sampling, be less microphonic than 12AX7 (or
12A?7 family) used for the same purpose? My knowledge of this is only
from a small sampling using a handful of amps, tap tests, and spare
tubes. But I'm hearing my handful of 6S?7GT tubes to be less prone to
microphonics than my handful of 12A?7 tubes. Is this true? Are the
internals generally more physically stable in 6S?7GT than 12A?7 ? Will
GT dual triodes, becuse of their greater parts mass, be less prone to
microphonics than smaller dual triodes? Anyone ever notice this? (Of
course I just might have some bad 12A?7's here and some really good
6S?7's.)

[Peter Wieck]

RickH wrote:
> Are larger GT tubes (in mass sampling) less microphonic than 9 pin
> tubes used in preamp and phase inverter stages?

All other things being equal, yes.

Bad Octals vs. Very Good 9-pin miniatures are exceptions, of course.

Very good of both will be near-equal.

But the greater mass and greater internal clearances of the larger
tubes are a significant advantage against microphonics.

Choose your tube for its operating characteristics and suitabilty for
your purpose, then screen until you get good ones. Pure and simple
tendencies towards microphonics is no reason to reject one tube or
choose another.

Peter Wieck
Wyncote, PA

[RickH]

Peter Wieck wrote:
>
> Choose your tube for its operating characteristics and suitabilty for
> your purpose, then screen until you get good ones. Pure and simple
> tendencies towards microphonics is no reason to reject one tube or
> choose another.

True, and suitability to purpose might include a bass combo amp, where
there would be significant vibration going on that might give the GT
the nod over a mini.

[Iain Churches]

"RickH" > wrote in message
ups.com...
>
> Peter Wieck wrote:
>>
>> Choose your tube for its operating characteristics and suitabilty for
>> your purpose, then screen until you get good ones. Pure and simple
>> tendencies towards microphonics is no reason to reject one tube or
>> choose another.
>
> True, and suitability to purpose might include a bass combo amp, where
> there would be significant vibration going on that might give the GT
> the nod over a mini.

I think it depends upon the gain of the stage. Both types can be
potentially problematic in mic and RIAA stages but be fine in say a
mu-follower.