[Collins] 516F-2 Query

[wabate]

Keep an eye on your filament voltage as you reduce the B+.  Filament 
voltage is the governing factor, at least that is how I feel.  Even with 
my design of the Heyboer, I went for the proper 6.3 with the primary tap 
and let the B+ go wherever.  Over voltage on the B+ is not good but even 
worse on the filament.

I used a 40V zener on the HV center tap of my R-390A supply to get it 
under control after the military replaced the expensive tube rectifiers 
with diodes.

73,

Bill, K3PGB

Dr. Gerald N. Johnson wrote:
> 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
>>
> 
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