[Collins] Another 516-F2 PS Question

[Al Parker]

once agn, thanks Jerry,
	Tnx for your always great technical explanations.
	I'll try the 2x 5v fil. winding bucking arrgt., probably next wk.  I've 
used bucking b4, and agree that it's better than Variac.  I've worried 
about the HV values to the KWM-2 & S-line for a while.  Haven't done it 
in the Halli rigs due to their internal problems.  Our line voltage is 
pretty steady at 125vac.  I oughta use a big 12v xfmr to buck the whole 
shop and shack supplies.
tnx, 73,
Al, W8UT

On 11/10/2015 5:33 PM, Dr. Gerald N. Johnson wrote:
> I like to lower the line voltage with a bucking transformer taking it
> down 6 or 12 volts. That service bulletin says the PA bias will have to
> be readjusted and that the load should never have a SWR over 2:1. A 6
> volt bucking transformer would drop the voltage enough to account for
> the different in drop between vacuum and silicon rectifiers, I'd like
> another 6 volts because the power companies have raised line voltage
> from 115 to more like 124 to allow for big loads to drop the voltage
> without it going under 110 that regulators would call bad. Typically the
> pole pig has about 4% impedance so there's a potential for 4% change in
> voltage if its primary voltage holds steady. Its usually not regulated
> at that voltage, though but is regulated at a higher voltage so there's
> another transformer with that 4% impedance so the load voltage varies at
> least 8% and regulators want it to stay above 115 or 110 depending on
> the jurisdiction and that high line voltage makes for high power supply
> voltages when the power supply was designed for 115 volts input, so a
> variac or bucking transformer helps keep voltages under control. I
> prefer a bucking transformer to a variac because its not going to get
> the knob turned by a visitor who has no idea what it smokes. And a
> bucking transformer is usually cheaper than a variac. Any filament
> transformer can be used as a bucking transformer if it has enough
> current rating. I think W5USI uses the two rectifier filament windings
> in the 516F-2 for bucking when converting to silicon rectifiers.
>
> 73, Jerry, K0CQ, Technical Adviser to the Collins Radio Association.