[AMRadio] Everyone know this but me?


Donald Chester k4kyv at charter.net
Sun Aug 14 00:13:59 EDT 2016


> Doing research on boost/buck transformers, I learned that it is not the
120
> volt load that determines the KVA needed, but the load on the lower
voltage
> winding that does the boosting or bucking.  This only applies when wired
as
> an auto- transformer, SOLA rates their 120 volt .25KVA unit at 20.8 amps
at
> 120 volts.  You can put your whole vintage station on one and get 1950's
110
> VAC for 50 bucks or so for this size unit from several sources.


A  10-volt 20-amp filament transformer will work just fine.  If 10 volts is
not exactly the bucking voltage you need, you can feed the primary of the
filament transformer with a much smaller variac,  to adjust the total output
voltage to just the right value.

A variac feeding the load directly does the most work when the voltage is
adjusted somewhere around mid-scale.  If the voltage is set close to zero or
nearly to maximum, the variac does very little work.  In fact, if the output
voltage of the variac is set to exactly the same is the line voltage, the
variac does no work at all,  merely acting as an inductor bridged across the
power mains.


Don k4kyv



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