[Amps] mega mobile

[R.Measures]

On May 3, 2004, at 2:09 AM, peter.chadwick at Zarlink.Com wrote:

>
>
>
>
> Rich said:
>
>> =F0  Triodes have Mu, tetrodes have Gm.
>
> Any tube with more than 1 grid has a mu.

=F0  Good point, Peter.  However, triodes are rated in Mu and tetrodes=20=

are rated in Gm.

> How relevant it maybe is another
> matter.
>
> mu is dVa/dVg, and is also  gm times ra (mutual conductance times
> anode/plate resistance)
>
> In a pentode or beam tetrode, where normal operation produces a =
virtual
> cathode between screen and plate, plate voltage has relatively little
> effect on plate current, and thus ra is very high and so is mu. =
Several
> transmitting tubes have a relatively low ra - the 6146 comes to mind -=20=

> so
> varying plate volts does affect plate current to a much greater extent=20=

> than
> in a small signal pentode such as a 6BA6. But gain is still
>
> (mu times Ra)/ (Ra + Rl)
>
> Rl is the plate load impedance.

=F0  yea, verily

Richard L. Measures, AG6K, 805.386.3734.  www.somis.org