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[Amps] amp with push-pull output and magnetic coupling to the antenna

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Subject: [Amps] amp with push-pull output and magnetic coupling to the antenna
From: Gene May <>
Date: Wed, 26 Jan 2011 16:36:50 -0500
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I have two related questions relating to the subject above, and would 
appreciate advice.  In more detail:  I am beginning the design of a 160 - 10M 
amplifier that will be cathode-driven, push-pull, probably use tetrodes 
(tentatively 4CX600J's) and couple the tubes' tank circuit to the antenna 
circuit with what is often nicknamed a "swinging link".  A "swinging link" 
would couple the antenna circuit coil magnetically to the tubes' tank circuit 
by having the antenna coil on an arm that swings or meshes in and out of a gap 
in the tank coil; the amount of coupling is varied and mechanically adjusted by 
changing how far or deeply the coils are meshed together.  Around fifty years 
ago and more, this was a common technique.  However, as many readers of this 
probably know, it is, ah, "uncommon" now.  I have looked far and wide for the 
mechanical components to accomplish this, unsuccessfully.  Now the specific 
1.  Does anyone know of a source for components or parts that could be used to 
make such a system?  I am willing to consider taking it/them out of existing 
assemblies (e.g., military surplus) but would prefer assemble it from "basic" 
parts.  I won't go so far as to say I'm desperate, but after considerable 
looking, I am very flexible and open-minded.
2.  It is necessary for the Q's of the tube circuit (probably to be around 10 
to 15) and antenna circuit (probably to be around 1) to be compatible with the 
range over which the coupling coefficient between the two coils could vary.  As 
I understand, it is difficult to impossible to get coupling coefficients higher 
than about .3 using coils that would be compatible with the voltages and 
currents associated with an output of 1.5 KW.  Comments, please?
TNX ES 73,
Gene May
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