> None of these characteristics was exceeded (1KW output, 4KV DC under
> 800mA).
>
> I can't understand the reason of this incident.
The plate choke was "series resonant". In that mode, the choke
acts like back-to-back L networks. The capacitance at the center
of the choke forms the capacitor of the L networks.
That makes the choke have extremely high voltage at the center,
and extremely low impedance from end-to-end.
The choke can also go into higher order modes, where it acts like a
longer series of back-to-back L networks.
If you measure the chokes impedance, while the choke is mounted
in place, you will almost certainly find the impedance is very low at
ten meters. One solution is to remove turns at the point where
stray capacitance is causing the problem. You can find that point
by running a screwdriver blade near the choke and watching the
resonance on ten meters. When you find the hot spot, the
resonance will suddenly shift.
Adding or removing stray capacitance in this "hot" area will have
the largest effect on the bad spot while affecting the rest a
minimum amount.
73, Tom W8JI
w8ji@contesting.com
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