>Hi Everybody,
>I am doing some experiments with tuned input circuits and was wondering if
>anyone might be able to help me. I am looking for some reference or
>resource to help with this.
>
>I have Excel spreadsheets from other folks in the reflector for designing
>tank circuits and am sure these can be adapted for tuned inputs.
>
>If I am incorrect, please let me know. I guess these formulas could be
>used, but kind of in reverse - match a 50 ohm input load to keep the radio
>happy, to the input impedance of what ever tube(s) may be used. My
>questions:
>
>1. Is this a correcct assumption?
>2. Where/how can I calculate the input impedance of the tube(s) used, say
>4x572-B, 3x8874, or 3x8875?
>
? Input Z is an average of the instantaneous E/I cathode input ratios
during the 360º of the sinewave driving-cycle. Typical numbers are 25?s
at the neg. crest to >1M? at the positive crest when the tube is cutoff.
To find avg. Z, build a low-pass Pi-network with a Q of c. 2 - 3 (XC-in =
16 - 25 ?s), adj. L and C-out for minimal SWR, shut down, measure the
values with a L-C meter, and calculate the Z-ratio of the Pi-network.
good luck, Jeff
- R. L. Measures, a.k.a. Rich..., 805.386.3734,AG6K,
www.vcnet.com/measures.
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