[Hallicrafters] (was Price of) SX 28 & Variacs

[Todd, KA1KAQ]

On 2/12/06, roy.morgan at nist.gov <roy.morgan at nist.gov> wrote:
> Quoting John King <k5pgw at yahoo.com>:
>
> > Have located a hallicrafters SX 28 receiver. Haven't
> > seen it and don't know electrical or physical
> > condition. Fellow, who has it, asked me to call him
> > back in about a week. He is going to put it on a
> > variac and bring it up slowly to see if it functions.
>
> NO NO NO SOP HIM NOW!!!!
>
> Or: start looking for a power transformer to replace the one he burns up.
>
> Roy

Someone get Roy his meds.....

Variacs, guns, cars, radios, paint, etc are not bad. How they are used
can be, but using one doesn't automatically put it in the 'bad'
category - regardless of how much punctuation is added.  (o:

I've yet to witness anyone wildly cranking up a Variac beyond the
necessary 115/120 volts and frying a transformer, or leaving it on
when there is an obvious problem (BZZZZZZZT!). Amazingly, I've never
done it either. I like to believe that most other old radio nuts, like
myself, have some amount of self control, common sense, focus, etc.
which kicks in at the appropriate time to prevent that crazy-eyed
override of control that allows the smoke to escape from whatever is
attached to said Variac.

What is more an issue is the fact that many old tube rectifiers don't
actually begin to function until they hit 90 volts or so, which still
slams the radio with a goodly jolt of power (after a presumed long
hibernation). If the goal is to reform electrolytics, there are indeed
better ways that include isolating them from the circuit, applying and
gradually increasing voltage over time, and monitoring the progress
with proper metering.

If the goal is more to give the radio a quick 'smoke test' (is this a
test to see if the smoke is still inside or to check for leaks?) as
most are tempted to do, at least the Variac approach gives you some
control and allows you to turn it back to zero before reaching the
full voltage if there are signs of trouble (see 'BZZZZT! above). I did
this a while back with an old Super Pro that functioned fine for a
while, but then began to stink when an old cap and the associated
resistor decided to join the local union.

Unless you're retired or independently wealthy with endless time on
your hands, chances are good it could be a while before you find time
to take the radio apart and check each component before applying
power. I have a number of rigs awaiting restoration, some of which I
still use. And from talking with Roy, I think he has an even longer
queue than me of future projects. If you use a Variac, there are a few
steps you should take ahead of time to be safe:

 - check to see how it is wired as most can be wired for a voltage
output other than what is on the dial and some have reversible dials

 - meter it, or at least check the output voltage against the dial to
see how accurate it is (mine is metered and I can't imagine using it
any other way)

 - check your own AC voltage at home as this can impact the
performance of your Variac

 - like anything else, use it appropriately for testing and don't rely
on it to regulate your voltage long-term (knobs can get bumped or even
cranked by other hands). If you want to regulate line voltage, try a
SOLA transformer or find a way to fasten the shaft in place so it
can't be moved.

I figure anyone who is using one of these things already knows this
stuff, but hopefully we can Roy in off the ledge before it's too late.
Especially with all of that nice TMC gear he has waiting for him.

73,

de Todd/'Boomer'  KA1KAQ