The Henry 3000D is an industrial RF generator.
It was never designed to operate above 20 meters.
The tube socket and metal chimney add much to the
already high "C" values on the 3CX3000A7 and to stray
C. That is why the 8-K Ultra uses no C1 in the Pi-L tank
on 10 and 12 meters. Henry designed a low-C socket and
non-metallic chimney to increase efficiency in the 22-30 mhz
range. I buy these items from Henry when I need to make
the Henry generators work above 20 meters.
I have personally stood behind Paul Johnson in the Henry
amp development lab watching him select tank values. He uses
a "little better" box than an MFJ-259B, but the principle is the same.
A resistor equal to the desired plate load impedance is clipped in
between the tube anode and chassis ground. When the tank is
resonated at the frequency of interest, the test meter attached to the
output of the amp will read 50 ohms. Now one must measure or
calculate the Q of the tank to make sure it is in the desired design
range.
Just because a match can be obtained in the above manner is not
enough. The Q could be 45-50 or more!
(((73)))
Phil, K5PC
Subject: Re: [AMPS] 3CX3000A7
>
> >A question was ask on how I determined the value of the resistor to >use.
> >I took the tube manufacture data sheet used the resonant load >impedance
> >and driving impedance values. Simply took that value in a >carbon
> >composition resistor and attached them to the circuit in there >prospective
> >location, I gave the MFJ what it wanted to see in order to >achieve a
> >resonant circuit.
> >I hope that made sense.
>
>
>
>
>
> I hope you either did this with tube in place, or used another capacitor to
> simulate the Cin, Cout and Cstray.
>
> Otherwise, we might have just found your problem :)
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