[AMRadio] Today's AC Mains voltage too high for many BA Rigs

[Donald Chester]

>From: "Jeffrey J. May" <jeffreymay at worldnet.att.net>
>... 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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