Mounting A Variac

From lwilto–(at)–IX.com Sun Jan 21 12:20:11 CST 1996
From: lwilto–(at)–IX.com (Loren Wilton)
Newsgroups: rec.audio.tubes
Subject: Re: Yowsa! Finally got a variac!
Date: 21 Jan 1996 11:44:29 GMT
Reply-To: lwilto–(at)–IX.com (Loren Wilton)
X-Newsreader-Author: lwilto–(at)–IX.com (Loren Wilton)
This message has been posted with development version software.
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In article ,
“Carson Block (Loveland Public Library)” wrote:
>
>On the diagram on the unit, a squiggly line (representing the
>x-former?) reaches from terminals 2 to 4, and pointing out from contact
>three is an arrow. I’m guessing that the arrow
>represents the brush on the back of the variac. I’m also guessing that I
>want to connect terminals 2 and 3 to the wall ac, and then terminals 3
>and 4 to the unit I want to apply the varied voltage to.

The “squiggly line” does indeed represent the coil of the variac. You
connect the input from the power cord directly across this winding. So the
power would go to pins 2 and 4, NOT to 2 and 3. (Getting this part wrong
could easily fry the variac, and possibly anything connected to it — which
might include you!

The output to your amp or whatever is connected from the common side of the
primary input and the arm. You neglected to say where the arm (the pointy
thing) is connected, but I assume it is pin 3.

>So, am I barking up the right tree, or will I end up frying myself!? If
>I’m right, what is the propoer way to connect 3-prong cords?

You want to mount the variac in a case. it shoudl be reasonably solid, since
a variac is fairly heavy. It could be metal or wood, it really doesn’t much
matter. There should probably be some minimal ventilation, especially if you
make a wooden box out of plywood or whatever, since wood doesn’t conduct heat
well. For a 2 amp variac used within its rating this really won;t matter
much. On a 10 amp variac it would.

Now, for the connections. The green ground wire of both the input and output
cords shouold both go to the same place, and this place should be connected
to the metal frame of the variac. NOT to any part of the coil or arm. This
is the safety ground.

One end of the variac is the “low” or “common” end. The other end is the
“high” end. With the shaft facing you, turn the knob all the way left, just
like turning down a volume control. The arm will be at one end of the coil
winding. Figure out which pin — 2 or 4 — this end of the coil is connected
to. This is the “low” end of the coil. The other is the high end.

Connect the white wire from both the input and output plugs to this “low” end
of the variac. Both to the same pin.

Connect the black input wire to the “high” end of the variac.

Connect the black output wire to the arm of the variac.

Loren