[Amps] PA choke design

[Vic K2VCO]

Regarding the option of making the choke part of the circuit:

Many commercial amps actually do this, because the reactance of the chokes they use is 
comparable to the load impedance of the tube. My thought is that this is NOT a good idea, 
because what you are doing is making a very low-Q component -- the choke -- part of the 
tank circuit. So I expect it will heat up from the circulating current and waste power. It 
could even burn out if it's not husky enough.

This could be one reason why some commercial amps make the most power on 40 meters, 
dropping off when you go higher or lower in frequency.

On 6/28/2011 8:26 AM, pc5m, Carel wrote:
> Hi, I know it has been discussed before, but can't find any good pointers.
> For  my single band 160mtrs PA I would like to  design the plate choke
> inductor. I would like to get the group opinion on
> - using a long/big normal air wound coil to get around 1 mH (coil  not
> involved in "matching" i.e. impedance well above circuit impedance at the
> anode. 1 inch wide/several inch long/500turns)
> - using a smaller air wound coil such that the choke will become part of
> matching circuit, RF currents flowing in this case.
> - using a ferrite core to get a smaller package. Not sure how big a ferrite
> core I would need to keep 1mH of inductance even when several amps of  DC
> current are present (saturation).
>
> In this case I am not too concerned (I think..) of parasitic resonance's of
> this coil, as long as it is a good inductor at 2 MHz : - )
>
> Any ideas ? pro - con's ?. Tnx, Carel.
>
>
>
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-- 
Vic, K2VCO
Fresno CA
http://www.qsl.net/k2vco/