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[AMPS] variacs

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Subject: [AMPS] variacs
From: (Tom Rauch)
Date: Thu, 5 Apr 2001 09:56:42 -0400
> I have a HB B+ supply that uses a variac on only one side of the 240
> vac. It is a 115 volt unit rated at 18 amps. Works great. With the
> variac in line I only drop 100 volts more than w/o. The dc filter
> network is a copy of the Henry 2K, 3K, et. and is a resonant choke
> with 32uF of cap after it. I tried a 240 vac 10 amp like the one used
> in the ARRL Handbook but it was dropping an additional 250 volts.
> Since it has step-start and I do not need to go below 2500vdc I
> decided to go with the 18amp unit on just one side of the primary and
> it improved regulation quite a bit. I like the freedom the variac
> gives me.

It has been pointed out several times that with a choke input the 
loss of regulation from using a variac is generally minimal. In many 
cases it is acceptable.  

Capacitor input supplies are another story. You'd better use a very 
large variac if you want minimal affect on regulation.

73, Tom W8JI 

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