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Re: [Amps] mega mobile

To: peter.chadwick@Zarlink.Com
Subject: Re: [Amps] mega mobile
From: R.Measures <r@somis.org>
Date: Mon, 3 May 2004 07:08:32 -0700
List-post: <mailto:amps@contesting.com>

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

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