[Amps] RF Chokes

[Vic Rosenthal]

Angel Vilaseca wrote:

> It is interesting to see that lots of literature have been written about
> the plate choke and almost none about the output choke. Both chokes are
> in a circuit with high currents and voltages. Both are wired between a
> high RF point and RF ground. It seems that the worst problem with the
> plate choke - resonance - is simply not an issue with the output choke.
> Why?

The 'output choke' is not exposed to high RF voltage.  A legal limit amp 
operating into a 50-ohm load with a reasonable SWR will have less than 500v at 
this point.  And there is no DC current normally flowing in this choke.  It's a 
very lightly-stressed component (unless the blocking cap fails).

Series resonances are problematic because they show a very low impedance.  But 
'low' is relative.  In the 50 ohm part of the circuit, a much lower impedance 
can be tolerated.  So although a series resonance right smack in a ham band 
would be undesirable, you wouldn't have to be very far off of the resonant 
frequency to have a high enough impedance that it could be ignored.

I don't see any reason to not use a toroid.

-- 
73,
Vic, K2VCO
Fresno CA
http://www.qsl.net/k2vco