[Collins] PM-2 supply question

[Dr. Gerald N. Johnson]

The transformer in the PM-2 is quite a bit smaller than the transformer 
in a 516F-2. A transformer has considerable thermal inertia and so can 
be operated overloaded with a more rapid heat rise than with rated load. 
This is true of all transformers between the iron core and the copper 
windings. Generally the life of a transformer depends on the peak 
temperature reached by the organic (often a form of paper) insulation. 
Power companies figure running a transformer to twice ratings an hour at 
a time occasionally (but it has more thermal inertia than the PM-2 
transformer) cuts its life in half.

I expect the op manual for the PM-2 is quite clear on use of RTTY and CW 
and phone. Speech processing is probably not included. I'm sure there is 
a temperature rise specification for the transformer, which might be 
printed on the transformer, surely is in the Collins specification for 
the transformer which we don't have.

You can cut back on transformer heating by turning down the drive. Go 
for 127 mils plate current on CW or RTTY, instead of 250, go for a peak 
output on SSB of 50 watts instead of 100 watts and the transformer will 
like the treatment and last longer. But since losing the PM-2 
transformer is an expensive disaster, why abuse it at all? Don't run 
RTTY, don't run a SSB speech processor and it will last its normal life.

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

On 4/12/2010 12:59 PM, wabate wrote:
> The Collins literature I have list the PM-2 as a lightweight supply.  In
> the specs, the high voltage spec is 'key down intermittent'.  Beyond
> that I can't find any info.  Was there an on/off spec for key down?
> Obviously, cw and SSB were considered intermittent.  I can probably rule
> out RTTY but how abort speech processing for SSB?  Is there a
> temperature rise spec for the transformer?
>
> Thanks,
>
> Bill, K3PGB
>
>
>