[Collins] Another 516-F2 PS Question

[Dr. Gerald N. Johnson]

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.

On 11/10/2015 4:19 PM, Al Parker wrote:
> Thanks Jerry,
> I'll go without it, in the AM. Your post brings up another question,
> I've seen the bulletin recommending SS diodes if rectifier tubes are
> flashing, and realize that the output voltage will be 10-15% increased.
> It seems that the increase of ~900vdc to over 1kv might be a bit much.
> I do that in other applications, e.g. Hallicrafters HT-32 & HT-37 xmtrs,
> because of their propensity to short the HV winding to a filament winding.
> thanks again,
>
> Al, W8UT
>
> On 11/10/2015 5:09 PM, Dr. Gerald N. Johnson wrote:
>> <snip>
>> In his KWM-2 book, W5USI recommends that capacitor be rated at 1600
>> volts with silicon rectifiers.
>>
>> 73, Jerry, K0CQ, Technical Adviser to the Collins Radio Association.
>>
>>
>
>