----- Original Message -----
From: "Roy Koeppe" <royanjoy@ncn.net>
> Just not true,
>
> I'm looking at published charts here, where at parallel resonance 'fo'
> (best situation), the choke exhibits more than 1 megohm effective
> parallel resistance to the tank. Down at the lower freq. limit of
> operation it still exhibits more than the 200,000 ohms. Nothing
> mysterious, and I'm sure the 3000 ohms of reactance is in SERIES with
> the resonant component (part of it). The use of resistance wire is news
> to me, but if it's true, I don't think it affects the fo at all. R is
> not even included as part of the L-C freq. equation. Besides, the slight
> amount of series R introduced would be swamped by say, 50 ohms of
> additional glitch resistor--I add this in response to your "concern"
> about Ohmite's possible use of resistance wire. The DC resistance of
> the choke is strictly limited by is dissipation rating.
>
> 73, Roy K6XK
>
It would appear that you are correct, Roy. I just looked at Bill Orr's
info on plate choke design (Radio Handbook 23rd edition, page 12-6).
While I knew that series resonant points needed to be avoided, I didn't
realize that typical plate chokes were purposely operated in a parallel
resonant mode. This explains why a properly operating plate choke
doesn't disturb the tuning of the plate tank circuit. If it weren't operated
around a parallel resonance, the series impedane would be nearly
equal to the plate tank input Z which would cause serious detuning
when inserted.
Sorry for the misinformation. Guess I have a bit to learn about plate
choke design.
Humbly,
Mike, W4EF
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