[ARC5] Use of a Variac

[Mark K3MSB]

 When bringing up an old radio I remove all tubes then bring it up using a
variac while monitoring current.  No need to bring it up slowly as this
tests the transformers for shorts.

After that I put the rectifiers in and repeat the process, although the
bringup is more slow.   Finally,  insert all tubes and repeat.

I don't reform caps;  I see no reason to do so with the availability of low
cost good quality capacitors.  If I want the aesthetics of how the original
cap looks,  I'll restuff it.

Mark K3MSB


On Thu, Apr 23, 2020 at 4:40 PM Richard Knoppow <1oldlens1 at ix.netcom.com>
wrote:

>     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
>
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