Re: [Amps] mega mobile

[R.Measures <r@somis.org>]

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

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

  Good point, Peter.  However, triodes are rated in Mu and tetrodes 
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 - 
> so
> varying plate volts does affect plate current to a much greater extent 
> 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.

  yea, verily

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

_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps