[AMPS] Cathode Impedance Measurements

[oz5tg]

>.......   using two 220 Ohm resistors from each cathode pin to ground and
>by leaving the tube in socket (driving impedance is 110 Ohms).  I could
>then use my MFJ-259 to tune my input pi-networks.
>


Jon, I have been working with Russian Triodes GS31 and GS35 on 144MHz
in grounded grid setup the last couple of years.

I estimated a input impedance of 150 ohm and used a Motorola transistor
matching program MIMP to model the components to the best result.
After installing the calculated components I tested the result with
resistors
and a MFJ-259, and found that I had reached the calculated result.

With the tube installed I was also able to reach a perfect input SWR, and
wideband
measurements indicated that calculated SWR far from 144 MHZ (+/- 25 MHz)
also was as calculated.

I think the method with resistors is valid and usefull.

By the way, who can give me a good method of presice prediction  or
calculation
of GG inputimpedance on VHF / UHF ???  I have a copy of an article from QST
December 1958 pg 32 - 35, but I find it hard to apply the method on VHF/UHF
with a reasonable amount of precision. The "guessing" method have until now
worked better for me.

Regards OZ5TG, Verner


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