ORIGINAL MESSAGE (may be snipped):
On Sat, 13 Apr 2013 15:28:13 -0600, Jim wrote:
> In fact, if the
>SRF is near 50MHx, you should have very little RF current through the choke.
REPLY:
The problem with a parallel resonant plate choke is not current THROUGH the
choke, it is the "ringing" or "circulating" current WITHIN the choke. That
current can be far in excess of the 1 amp rating of the Z-50, especially
when the plate tank is lightly loaded or accidentally overdriven.
The "Tesla Coil Effect" will suddenly make its appearance.
The best plate choke will have a reactance roughly about ten times the
reactance of the plate tuning capacitor, and no series or parallel
resonances near the frequency of operation. A good value for 50 MHz is
around 7-10 uH. This is not a critical value, but don't stray too far away
either.
More inductance is NOT better, since more turns will probably lead to
resonances closer to 50 MHz. All chokes of this type have both series and
parallel resonances and the trick is to use a small enough choke so the
resonances are well above the operating frequency and yet the reactance is
still high enough to not significantly detune the plate tank circuit.
Electronic design is both art and science. That's what makes it fun. :-)
Bill, W6WRT
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