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

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.

--
Nick

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

Ian Bell wrote:
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

Is that one or two dots?

--
Nick

In article , Nick Gorham
wrote:
Ian Bell wrote:


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

Is that one or two dots?

While you are at it, send him a copy of the noise plots I emailed as it
will save me scanning them again. :-) They show the 1/f noise quite
nicely, and demonstrate how it rises and dominates over shot noise as you
increase the bias current.

FWIW Ian I also tried cc'ing an email to you, only for it to bounce.

Slainte,

Jim

--
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Audio Misc http://www.st-and.demon.co.uk/AudioMisc/index.html
Armstrong Audio http://www.st-and.demon.co.uk/Audio/armstrong.html

Nick Gorham wrote:

Ian Bell wrote:
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

Is that one or two dots?


Just the one - slip of the finger ;-)

Ian

Jim Lesurf wrote:

In article , Nick Gorham
wrote:
Ian Bell wrote:


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

Is that one or two dots?

While you are at it, send him a copy of the noise plots I emailed as it
will save me scanning them again. :-) They show the 1/f noise quite
nicely, and demonstrate how it rises and dominates over shot noise as you
increase the bias current.

FWIW Ian I also tried cc'ing an email to you, only for it to bounce.

Slainte,

Jim



More slipping of the finger. I see from my own headers that my email is
given as when in fact it is

I don't often check it as it is basically a spam magnet so if you email me
there let me know via the group so I know to go look for it.

Cheers

Ian