From: "Jeffrey J. May" <[EMAIL PROTECTED]>
... I am thinking about using two heavy duty
automatic regulated Variacs on each line that will automatically adjust
within a set range..pricey though..problem is that my line voltage varies
enough that I am adjusting too often manually..Jeff..W0XV
I have the problem here. I have seen the voltage as low as 108v and as high
is 125. My main transmitter has a rheostat on the tube filament transformer
line feeding several transformers, but I have the same problem, having to
keep a constant eye on the thing and frequent adjustment.
Incorrect voltage won't burn out tubes right away, but the manufacturers
have warned for years that this will shorten useful tube life.
One solution I have thought of, and probably have all the parts for, would
be an automatic voltage regulator using a variac and reversible motor. I
have a relay that looks like a meter, but the pointer has two sets of
contacts, one of which will engage wenever the pointer is above or below the
set value which is adjustable with a knob near the zeroing screw. It's just
a matter of figuring out exactly how to build the thing and putting it
together. Minus the special relay, I have thought about using a VR tube and
comparing its voltage output to that of an unregulated power supply with the
same nominal output voltage. Of course, it could also be done using solid
state components.
One thought about using a variac. With most of the ones I have used, even
the HD ones, the regulation sucks. A tapped autoformer with a heavy duty
switch is better. Instead of using the variac to drive the equipment
direcly, it would be better to use a large, high current, low voltage
transformer@ about 15-24 vac/ 30 amps as a bucking transformer and use the
variac in the primaryof the transformer. That way you get better resolution
of voltage and better regulation. The problem with variacs is the carbon
brush contact. It must have a certain amount of resistance so that shorted
adjacent turns don't overheat, since the wiper contact must make before
break to assure uninterrupted output as the voltage is varied.
Don K4KYV
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