[Collins] 516F-2 Query

[Dr. Gerald N. Johnson]

Yes bucking will work whether using the well insulated filament windings 
or another transformer. Each filament winding is rated at 3 amps, not 
much above the primary current. So you won't reduce the resistive 
heating but will reduce the core saturation and its heat. A variac also 
works but unless its locked in position its a tempting knob for visitors 
to turn to see what happens and it can supply excess or two little 
voltage. Since the power handled by the bucking windings is proportional 
to the voltage change a 12 volt bucking transformer will handle ten 
times its power rating. There are buck/boost transformers made with 
120/240 dual winding primaries and either 12/24 or 16/32 dual winding 
secondaries that can be hooked in series or parallel.

A handy way to work out transformer connections is to use a 12 volt 
transformer to run the primary, then when you check voltages they will 
be 1/10th the normal and you don't get bit so bad  from the high voltage 
leads when you accidentally hit them and you get to connect the bucking 
windings with the wrong polarity without putting strain on the core and 
filter capacitors.

The resistor to drop the low voltage doesn't improve the voltage 
regulation. Though the tube drop in the rectifiers isn't a benefit to 
regulation either.

The relay for primary power is something it should have had from the day 
1. Or the way I built my HP supply with power switch on the supply 
chassis and I didn't connect to the switch in the 32S-1.

73, Jerry, K0CQ, Technical Adviser to the Collins Radio Association.

On 1/21/2012 12:29 PM, Byron Tatum wrote:
> Hello-
>      I am preparing to service a pair of 516F-2 supplies, for my (newly
> aquired) KWM-2 and 32S-3. My desires are to lower the voltages on an overall
> basis and to lower the heat load on transformer and components.
>      I am considering removing the tube rectifiers entirely and using diodes. I
> realize this will undesirably increase my low B+ and high B+ voltages, that are
> already too high to begin with. However, this of course gets rid of a lot of
> heat and the filament load on power transformer.
>      To bring down the voltages is it feasible to take the two 5 volt filament
> windings and use them to "buck" the primary of power transformer? I can't recall
> hearing or seeing of this done in a 516F-2 but have heard it suggested in a
> receiver power transformer once.
>      I have studied the Heyboer replacement power transformer for the 516F-2 and
> really like the tapped primary which allows you to counteract the higher line
> voltages of today.
>      If this is feasible I plan to use one rectifier spot for a relay to take the
> current load off of the on/off switch in radio.
>      In the past I have added the dropping resistor in the low B+ to at least
> help there, but I am looking for a better overall solution to the voltage and
> heat issues.
>                                                      Thanks, Byron WA5THJ
>