BUT
at 3.5 MHz, that 50 microhenries has an inductive reactance of 1100 ohms, and
needs an extra 50pF of plate tuning capacity. Now let's assume a plate voltage
of say 2500 volt and a minimum plate voltage at the bottom of the swing of 500
volts. That's 2kV peak or 1400 volts rms of RF across the choke or roughly 1.27
Amps of RF current in the choke on 80m - in addition to the DC. Now let's
assume a good choke with a Q of 150. That's about 7 ohms of RF resistance and
thus about 12 watts dissipated in the choke. Of course, it could be worse....
Now look at the bypass cap at the HV end of the choke. Assume a 0.005 mFd - not
an untypical value. That has XC = 18 ohms at 3.5 MHz so we have around 23 volts
of RF across the bypass cap - which needs to be rated for 1.3 amps of RF..
All of which is why you really need a choke - capacitor - choke - capacitor -
HV feed arrangement. OK, hams have got away without for years. So have a lot of
drunks who drive.....
I believe you need a much bigger choke or possibly a couple of chokes in
series......
73
Peter G3RZP
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