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Uunderhill
diyAudio Member

Join Date: Dec 2008
Quote:
 Originally Posted by DF96 gm and plate resistance are related: Rp = mu / gm Measure any two of these and you can calculate the third. You could measure Rp by varying Rs in your circuit and seeing how gain varies. Then, knowing Rp, you can calculate gm from your results.

Seeing this response was a good moment. I think it puts many things together.

for a tube - the small signal parameters are as follows

........................ mu = gm x rp

where, mu is the maximum theoretical gain for a particular tube.
and rp is the plate resistance

for the common cathode amp above, Rp is connected in the circuit, so substitute Av for mu - without a load, the gain is as follows.

........................ Av = gm x rp//Rp

However, a switch could be connected in series with a load resistor - Rs.
Measurements, could be taken - switching the load resistor in and out.

....................... Av = gm x rp//Rp//Rs
.

Last edited by Uunderhill; 15th October 2012 at 10:17 PM.

 16th October 2012, 10:20 AM #22 DF96   diyAudio Member   Join Date: May 2007 Yes.

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