[Collins] 516F-2 Query

[Dr. Gerald N. Johnson]

Thing is with line voltage higher than what the radio was designed for, 
the filament voltage is also high and tends to shorten tube life. But it 
is proper to shoot for 6.3 volts on the filament line under load, if one 
has an accurate AC meter for that range.

In a review and update of a solid state regulator design for the R390, I 
suggested mounting the pass transistors outside the radio to remove the 
heat from that voltage drop besides the heat from the pair of 6082 
heaters. Moving out that heat can't help but to reduce component aging 
and thermal drift.

73, Jerry, K0CQ

On 1/21/2012 10:50 PM, wabate wrote:
> 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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