[Amps] Plate Choke question

Carl km1h at jeremy.mv.com
Sat Nov 9 20:01:11 EST 2013

```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 at bresnan.net>; <amps at 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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