[Amps] Zero Crossing circuit

[Vic Rosenthal]

Ken Warren wrote:

> I tried a zero crossing controller in a 750 volt power supply prior to
> running it on the 3KV plate supply and my experience was that the
> laminations in the transformer made so much noise that it was not usable.
> The audio from the modulator caused the laminations to act as a speaker
> and it was loud enough to cause feedback. The transformer did have well
> sealed laminations. I would like to know if others have tried this also
> with the same result

If you are referring to a solid-state relay which switches at the zero crossing 
point (I'm not sure of the terminology), they are VERY sensitive to RF.  I had 
problems with the relay partly opening in the presence of RF.  In my case I was 
using it to control a linear PS which was powering a solid-state 750-watt HF 
amplifier, and the result was that the PS drew more current in an attempt to 
maintain regulation, which blew primary fuses.  When I noticed that this did not 
happen when transmitting into a dummy load, I realized that RF was the issue.

I had to bypass and filter both the primary and control circuits to solve this 
problem.  Maybe your noise was caused by the controller dropping out at an audio 
rate in response to the RF?

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