I just ran a simulation with a tube with a 3000 ohm impedance and 3000V
peak AC on the plate connected to a 100uH plate choke at 10MHz. The AC
current in the choke was about 440mA peak. Then placing a 2.533pF
capacitor in parallel with the choke produced a parallel resonance at
10MHz. The resulting AC current in the coil was now 490mA peak or about
a 10% increase. Of course the capacitor also had 490mA peak in it and
in a "real" choke where the capacitor is hidden in the inductor might be
hard to tell what the exact inductor current is but this increase in
current is not exactly a large increase. Considering that the AC
current rating of the choke falls off with frequency due to skin effect
which causes the resistance to rise as the square root of frequency and
that the parallel resonance occurs at a pretty low frequency I kind of
wonder if avoiding the first parallel resonance is really important.
Obviously avoiding all series resonances is extremely important.
Anyone care to actually simulate a circuit showing us how a parallel
resonance in the plate choke causes smoke?
73,
Larry, W0QE
Bill, W6WRT wrote:
> ORIGINAL MESSAGE:
>
> On Sat, 30 Jan 2010 20:17:16 -0500, "Gary Schafer"
> <garyschafer@comcast.net> wrote:
>
>
>> We usually don't care if the plate choke is parallel resonant or not.
>>
>
> REPLY:
>
> Oh, yes we do. If the choke has its own internal parallel resonance on
> a ham band, and it is made with small gage wire as they all are, smoke
> will surely follow.
>
> 73, Bill W6WRT
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