[ARC5] Use of a Variac

[Richard Knoppow]

    I think the idea of the Variac to bring voltages up slowly is 
based on not having filter caps short. I don't think it really 
works. What I used at -hp- and have now is a metered Variac. If 
something isn't right the current meter will come up too fast and 
I can hit the off switch quickly. Still won't protect something 
that has a shorted power transformer. I am also not a believer in 
re-forming electrolytic caps. While there is a long military 
treatise on this I think there are some assumptions made about 
how caps fail that are wrong. If you want to reform the caps do 
it with a variable, current controlled, DC supply with the caps 
out of the device. A metered Variac is very useful because you 
can tell right away if something is drawing excessive current, or 
maybe too little current. A dim light tester is better because it 
will show immediately  if something is shorting.

On 4/23/2020 1:18 PM, Robert Eleazer wrote:
> We frequently hear people suggest that you bring up the input 
> voltage on an older piece of equipment with a variac to allow 
> capacitors to fromate and so forth.  Of course this remains as 
> a somewhat controversial approach.
> I have a URM-127 that I need to recalibrate the frequency dial 
> and in the process of researching that procedure I found the 
> following:
> /a. /If the signal generator has been stored in excess of two 
> years, perform the following pre-test procedure to assure 
> proper operation of the power supply filter capacitor.
>
> (1) Operate the signal generator for 30 minutes at 57.5 VAC, 
> 60-400 Hz, 1 phase input.
>
> (2) Adjust the input to the required value using a variable 
> transformer between the power supply and the power cable. Check 
> input voltage prior to connecting to the signal generator.
>
> (3) Remove the variable transformer from the power cable and 
> connect the power cable to the electrical power source.
>
> Wayne
>
> WB5WSV
>
>
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-- 
Richard Knoppow
1oldlens1 at ix.netcom.com
WB6KBL