Ian Iveson wrote:
Ian Thompson-Bell wrote
snip

That's the thing. In a preamp, two tube factors contribute
to noise - gm and Ia so it is quite typical to run the
first stage at a very low current - say 1mA or less - and
the curves are unreadable in that region.

But not typical to use a 6AU6.

Ah but, strangely enough the 6AU6 IS/WAS used in audio preamps. It is
used today in a top of the range Sony condenser mic, see:

http://www.gigasonic.com/Sony-C800GPAC.html


Curves for an ECC83, for
example, are scaled appropriately for your application.
Compare with those for an ECC82, where scale is similar to
what you have for the 6AU6. That's why I assumed you where
talking about the driver end of the pre-amp.


OK. I too found the ECC83 curves are scaled appropriately and it is
basically an AF tube. The ECC82, though often used in audio application,
is basically and RF tube and as you say has curved scaled more like the
6AU6. I think that is the explanation why the curves I want don't exist.

Cheers

Ian