[Hallicrafters] Variacs continued

[Mark Shaum]

John has a good point here.

> I use a variac, not so much to reform caps (I disconnect the load and
use
> an external PS to reform them), but to carefully monitor powerup
current
> while bringing up an unknown piece of gear.


The one accessory you should have on the output of your variac is an AC
ammeter.  Many metered variacs on the market only have a voltmeter.  By
the time the fuse blows in the radio you are slowly powering up some
additional damage may have occurred beyond whatever was causing the
original high current draw.

And a better point is raised on overvoltaged filaments, which greatly
shortens tube life, particularly in the case of power tubes.  I aim at
running any power tubes at 10% under their rated filament voltage, which
by most accords will double the tube life.  In my SB-220, I have
resistors in series with the filaments (small scramble wound coils of
wire) to drop the filaments to 4.85 volts.  My line voltage is nominally
124 volts so I need to keep an eye on voltages.

I have a 10 volt 10 amp filament transformer set to buck the line
voltage which feeds an outlet strip for some of the radios, effectively
reducing the line voltage, but regulation does suffer a bit with this
arrangement.  I also have a big, heavy 750 watt Sola constant voltage
transformer as a more elegant solution but didn't like the amount of
heat it added to the shack.  It runs quite warm even with no load.

Mark K9TR