[AMRadio] Modulator


Jim Candela jcandela at prodigy.net
Fri Dec 14 19:03:26 EST 2007


>Sun, 09 Dec 2007 11:16:01 -0800Barrie Smith

		







>I've been thinking . . . again . . . about a modulator for the push-pull 
>VT-127A rig.

>I have all the parts from the KW modulator I used with the push-pull 450TH rig 
>I built many years ago, so I could rebuild it.

>I don't see anything wrong with using a big modulator with a small RF deck, but 
>perhaps some of you fellows can point out the pitfalls.

>I know that I'd have to adjust voltages to match the loads, but that appears 
>doable.

>Any comments?
>73,
>Barrie, W7ALW, DN36au,
>QRV 6M, 432 & 1296 EME


Reply by Jim WD5JKO,

Barrie, I noticed that your post went unanswered. What you are suggesting is similar to putting a Big Block Chevy 454 into a  VW Beatle.  Actually I know a person that did just that into a Corvair. It took him years to weed out the bugs. He had the engine in the back seat too!

As for your modulator idea, why not. This would be easier If you have a variac for the plate supply, and a means to adjust the grid bias (regulated supply - shunt regulated type), and  a multi-match mod transformer.  I'd add spark gaps between the plates at the mod transformer, and add some sort of negative cycle loading that kicks in whenever the modulated B+ drops below zero, or better yet at about 10% of the unmodulated B+ value. This will allow for some asymmetrical modulation

Go for it!

Regards,
Jim
JKO

 




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