[AMPS] TRIAC

[Peter Chadwick]

Monty asks:

	>My questions;
	>1.  Has anyone ever used a TRIAC Unit to bring up an Amplifier to
reform >the Capacitors.?
	>2.  Does anyone know of any circumstances that I should use only
the >wire-wound VARIAC
	>and not a TRIAC unit.?


 I think a lot depends on whether its phase control or burst control. In
phase control, you turn the triacs on for part of the cycle only; in burst
control, you turn them on for a complete cycle, usually at the voltage zero
crossing point, and you vary the average voltage by how many cycles you have
on and off: f'r instance, if you turn them on every other cycle, you get
half the voltage ON AVERAGE. Phase control is a lot nastier from an RFI poin
of view, because you can be switching at the maximum voltage point.

I worked on an amplifier years ago with SCR control on the transformer: that
was 415 volt 3 phase, and the supply was 18kV at 3 amps. (For Rich's
benefit, we never took any measurements or precautions against X rays! - but
that was in 1966 - the world was a lot more lackadaisical then). These were
phase controlled, and we didn't have any problem.

I guess the bottom line is that I would try it.  I wouldn't use a variac in
normal use, because of the regulation problem, and I wouldn't use the triac
unit in normal use because of the RFI possibilities. But for slowly bringing
up the supply for reforming/testing the caps, I don't see a problem. I must
admit that i have inherent dislike of phase control, since the idea of
repeatedly switching the volts at the peak of the cycle (if you want half
volts) seems to me to be cruel to transformers - and rectifiers. Still, it
is used successfully commercially.

73

Peter G3RZP



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