Variac

[J Forster]

Generally I agree with your comments. In a recent conversation with a technology museum
curator, the difference between 'conservation' and 'restoration' was pointed out to me.
IMO, conservation is good, restoration is not.

Anyway, after a thorough visual check, I pull the rectifier tubes, and then apply line
power from a power limited source, like a lamp and variac. If that's OK, I apply B+
stepwise with the filaments off and reform the capacitors. Only then do I put in the
rectifier tube and apply AC carefully.

FWIW,
-John



Greg Gore; WA1KBQ wrote:

> It depends on the particular piece of equipment in question. No harm would
> be done at all if a Hallicrafters SX-100-101A or any Collins receiver was
> recapped and it would result in a better working more serviceable unit. On the
> other hand, what about a Hallicrafters SX-10 (200 made) or an RME-9D
> (individually hand built), or National AGSX, Breting 14, Sargent 21MA, or a  McMurdo
> Silver 3A? I used to believe every receiver should be recapped until I  realized
> important history was being discarded and lost forever when my goal was  just
> to put it back on the shelf with a "ready" tag and never to be plugged in
> again. Antiques have more value if left entirely in their original state or with
> a simple replacement filter network that can be easily reversed. The problem
> as  I see it with component replacement or re-stuffing work is very seldom do
> you  find workmanship that is up to the standards of workmanship of the
> original. Now  I realize most of these things were soldered together en-mass by
> women  assemblers but they did it every day perhaps thousands of times and the
> quality  and appearance of their workmanship is a part of the history; they did a
> better  looking job than most of us can do. I now prefer to check an antique
> for signs  of life regardless of quality of working order and I consider it a
> plus if any  is found.
>
> For example: I have a completely original Hallicrafters S-1  Special here.
> This was Bill Halligan's first "hallicrafters" communications  receiver and
> there is currently only two Specials known to exist. I have  established that the
> receiver exhibits a loud hum. This is good enough for me. I  could easily make
> it work again but why in the world would anyone want to? The  S-1 could
> probably be outperformed by an Ocean Hopper. The historical value of  this receiver
> far exceeds any questionable noble intent on my part to "make it  work again."
>
> When checking any unknown antique for the first time I  recommend cleaning
> the set first followed by a good visual inspection. Look  carefully at all point
> to point wiring and physical appearance of all  components. If you see a
> damaged component or a charred resistor you don't  proceed with power for example.
> Power the set in steps through a 100 watt light  bulb followed by a variac;
> maybe first without the rectifier tube to get an  indication of the transformer
> first. The 100 watt bulb will protect the  transformer from damage if a fault
> exists. Next I usually plug a  substitute solid state rectifier in the
> rectifier socket for additional safety  because it allows me to start testing at
> lower input voltage but this is not  entirely necessary if you carefully monitor
> the behavior of B+ while advancing  the variac. Rectifier tubes begin to
> conduct B+ at around 50 volts on the variac  setting and B+ will escalate very
> quickly with any small advancement past that  so be careful. I start with some
> measured B+ and monitor how responsive it is to  small advances of variac. If the
> filters are in trouble the B+ will be lazy and  slow to respond and the cap
> may start to get warm. Good filters will remain cool  and allow B+ to build
> quickly to normal levels. Be sure to check component temps  periodically too. Of
> course the plate and screen bypass caps will affect this  too but we are
> primarily answering the variac question here. There are other  means of determining
> if reasonably safe to run with old bypass caps. Usually it  is risky to run
> with old caps but I do it here all the time. Just like driving a  1928
> Chevrolet down the highway would be less risky with a modern replacement  engine and
> hydraulic brakes but I don't know of any antique car guys who would  want to
> experience a 1928 Chevrolet in that manner.
>
> 73, Greg
>
> PS- A better method would be to disconnect the filters from the circuit and
> test leakage current first before proceeding with power up.

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