Nick Gorham wrote:

Ian Bell wrote:
A while ago we were discussiig theoretical and actual measured noise in
the first stage of a preamp. RDH suggests the equivalent input noise
resistance for a triode is about 2.5/gm. Patrick noted he had never seen
noise anywhere near as low as this.

I have just read this article:

http://en.wikipedia.org/wiki/Valve_a...er_-_technical

which suggests the 2.5/gm only applies at frequencies above 10KHz and
that below this 1/f noise dominates. It also suggests this can be reduced
by choosing very pure materials for the cathode nickel, and running the
tube at an optimized (generally low) anode current.

Don't know who the author is and as a rule I take anything on wikipedia
with a large grain of salt. Comments?

Cheers

ian


Well, I did email you a document that included a reference (and origin)
for the 2.5/gm figure and the pentode version. But at that time your
email address attached to your post didn't seem to be valid.

So I gave up.


That's kind of you Nick. Could you send it to ianbellATukfsnDOT.org

Chers

Ian