BUT again, he clearly stated he was interested in 20-10M including WARC with
no resonances.
Anybody with a modicum of amp experience understands the basics and the
Heath choke fits the job.
It should be relatively easy to wind one also given the requirements as with
such a low inductance it would require a lot of work to have a resonance
below 30 MHz.
Carl
KM1H
<kk7uv@bresnan.net>; <amps@contesting.com>
Sent: Saturday, November 09, 2013 4:14 PM
Subject: Re: [Amps] Plate Choke question
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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