In Reply to: The formula: posted by Ralph on July 28, 2014 at 09:39:24:
Ralph
Sorry it is not that simple ...
You need to take into account the impedance
of the tube section that is in parallel
with the cathode resistor.
From the linked website -
It can be shown that the resistance seen looking into the cathode (Rk unbypassed) is:
Rk' = (Rp+ra)/(mu+1)
Therefore, the total cathode resistance, or the output impedance if you take the signal off the cathode, is the parallel combination of the cathode resistance, Rk', and the cathode resistor, Rk, as below:
R = Rk' || Rk
DanL
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Follow Ups
- RE: The formula: - danlaudionut 09:52:58 07/28/14 (2)
- Oops! Thanks for pointing that out nt - Ralph 11:35:53 07/28/14 (0)
- RE: The formula: - Tre' 10:46:20 07/28/14 (0)