[AMRadio] Home brew AM Cathode modualtion

Donald Chester k4kyv at hotmail.com
Sun Oct 3 13:45:01 EDT 2004

>The 450th is a big triode, so I don’t think you can run it single ended pie 
>net output, you would need to do 2 250th tubes in push pull or something, 
>but the 450th would do the cathode modulator quite well.

You could use a single-ended pi-network type output circuit, with a balanced 
grid tank coil.  That is knows as "Rice" neutralisation.  You don't get as 
perfect null as you can with a balanced plate tank cincuit or a pushpull 
arrangement, but it works well enough that it became the standard design of 
tube type broadcast transmitters starting in the late 50's.

I used that circuit with the first high power rf final I ever built, using a 
304-TL in the final, because I didn't have a large split stator tuning 
capacitor on hand.


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