Robert,

Yeah, the original 12AU7 was making a lot of noise through the output
trannys. I replaced it with a cheap new one. About 90% of he noise
disappeared, and the noise that remains has a slightly different character.
I just want to find a very very quiet replacement.

Thanks!
--
Stephen Boyke

in article , Robert Casey at
wrote on 4/16/04 9:39 PM:

Stephen Boyke wrote:

I've purchased a microphone for recording (CAD VX2). It uses a 12AX7
for the head amplifier and a 12AU7 to run the line driver. I'm interested
in getting different brand tubes for it (the current X is a Sovtek and the
current U is a Phillips). The Phillips makes lotsa noise and is defective.

Anyway. Does anyone have any suggestions? I'm looking for very very
low noise, low microphonics, etc. To the extent they can add as little
color to the sound of the circuit as possible, the better.



As Phil noted, tubes can be noisy, but from your discription, you need a
new 12AU7.
But how do you know that? Does the noise remain if you remove the
12AX7? Are the
tubes inside the microphone itself (I'm not familiar with the CAD VX2)?
Maybe the
mic element itself is making some of the noise?

As for what brand of tubes to get as replacements, That's more a matter of
opinion than anything else. NOS tubes made during the tube era might be
good bets. Mil spec tubes might have better microphoonics and noise, but
in the late 70s lots of bad tubes were made for the military.... Many
were ordered,
delivered and never used.