[Collins] Bucking Voltage

[Dr. Gerald N. Johnson, electrical engineer]

There are two 5 volt windings in a 516F-2, isolated from each other and
from ground. They would have to be unhooked from the tube sockets
because a solid state rectifier plugged into the tube socket would be
using a cathode pin for the DC out of the rectifier. The two 5 volt
windings in series would make a 10 volt buck for the line voltage and
can carry the current with no problem. They would drop the output
voltage more than the solid state rectifiers would raise it and would
lower the heater voltage and the transformer saturation for a cooler
running transformer core.

There's now way to know a priori which yellow and which slate to wire to
the other and to the transformer primary. The connections have to be
developed experimentally. I like to do such connection testing while
supplying such a circuit with 6 or 12 volts on the primary. Then I don't
have 1 kilovolt loose to burn my fingers... or worse.

What I'd do, with 6 volts applied would be to try the two possible
series connections of the 5 volt windings to get maximum voltage. One
connection will give nothing, the other will give 10 volts with full
line voltage, a half volt with 6.3 volts applied. Then I'd connect one
end of the series pair to the transformer primary wire I planned to use
and see if the voltage from the other transformer primary wire to the
free end of the filament pair was greater than the primary voltage. I'd
swap ends of the series pair (until I achieved that condition. Then I'd
unhook the power feed from that primary wire and make the connection to
the filament winding permanent (soldered and taped) as well as the
series connection of the two filament windings, and then apply power to
the free end of the seriesed filament windings. That's all there is.
Harder to describe than to draw or do.

73, Jerry, K0CQ, Technical Advisor to the CRA.
-- 
Entire content copyright Dr. Gerald N. Johnson, electrical engineer.
Reproduction by permission only.