Jim Lesurf wrote:

Eeyore wrote:

Ian Bell wrote:

So apart from the possible variation of gm with anode current, the
noise added by a triode seems to to fairly independent of anode
current. This seems strange to me since shot noise is caused by random
fluctuations in anode current so I would expect higher anode currents
to produce higher noise.

Not because of the shot effect for sure.

Erm... the shot noise level rises with the current level. The reasons for
this are well explained by theory.

Rises as the root of the current AIUI.

Therefore a doubling if Ia will result in an increase in In of 3dB.

However since it can normally be safely presumed that the signal level increases
with anode current too (ok not quite 100% directly with tubes), then actually,
the relative noise will *reduce* by 3dB i.e the s/n ratio will improve.

Graham