[Collins] PM-2 Xfmr upgrade - Its ready!

[Dr. Gerald N. Johnson]

On 10/6/2010 11:46 AM, wabate wrote:
> Sorry for the long delay in finishing this project.  I let work
> interfere with ham radio!  But the good news is that the upgraded
> transformer is finished testing and ready for manufacture.
>
> For those that missed or have forgotten the original email, I wanted to
> use a PM-2 power supply with my 2A but I was concerned about its
> intermittent B+ rating (Collins description, not mine).  Another concern
> was that the power supply was designed for 110VAC operation.  If you
> check the supply voltages, they will be higher than spec.  The only
> significant problem I found was with filament voltage.  On my stock
> supply with 120VAC input I had 6.8VAC volts under load!
>
> In 40 years or so since the original design, wire and insulation has
> improved dramatically.  The wire now used has a rating of 150 C and the
> insulation is rated cat 130 C!  The other improvement was in lamination
> efficiency.  The result was a transformer with the same size and
> voltages that I operated at full load for 3 hours continuous.  The power
> supply, with the new transformer installed, and under lock key had a
> filament voltage of 6.3VAC and DC voltages of 280VDC and 796VDC.
>
> I eliminated the 110/220VAC dual primary because I thought it had
> limited appeal and because it the allowed me to tap the primary.  The
> primary now has taps for 115VAC, 120VAC and 125VAC.  Now we can
> compensate for the higher line voltages that exist today.  I also
> eliminated the 400 HZ capability.

The higher efficiency laminations are probable better iron and thinner 
than the originals and probably limit the high frequency operation to 15 
kHz. The only thing about 400 Hz capability is that the iron ought to be 
thinner for lower hysteresis loss, but since the flux density in a 60 Hz 
transformer core at 400 Hz is 60/400 times the flux at 60 Hz, or 15% the 
flux, the loss is low anyway. Just you haven't required the maker to 
prove it will work at 400 Hz.

More than one 60 Hz pole pig is in a broadcast station serving as the 
modulation transformer or reactor and the station is passing performance 
tests with audio out to 15 kHz. Not redesigned, not rated, but

Fundamentally a power transformer is designed to put the power frequency 
at the low edge of its pass band to minimize the amount of copper and 
iron and with no special care its good to 10 or 12 kHz for HIFI 
standards. One of the design variables is the amount of core saturation. 
The best irons allow a much higher flux before saturating and then they 
saturate hard. But that minimizes copper and iron amounts.

Some fiddling with windings can help the higher frequencies a little, 
and is done in the best of tube audio output transformers, things like 
partial high impedance windings in sections interleaved from one side to 
the other to get exactly equal coupling which is not a concern in a 
power transformer.
>
> So what's the bottom line?  Well initially I got a price of $125 plus
> S&H.  After all the refinements and based on the initial interest
> expressed, the price is now $128 but that INCLUDES S&H.  So the price
> came down.  S&H is limited to CONUS.  Others can request S&H charges for
> outside CONUS.  Please note that this is a one time production run.  I
> will not be stocking transformers for future sales.  To get one you must
> order one (or more) now.  This is a hobby for me, not a business.  If it
> were, I would be marking up the price.  The price is just what I am
> being charged.

Sounds like a good project if one has a PM-2 needing a transformer or 
wants to work that PM-2 hard.
>
> To see the transformer and my upgraded PM-2 please go to:
>
> http://mysite.verizon.net/wabate/pm-2.htm
>
> You in effect have a 516F-2 in a PM-2 package.  Those who expressed an
> earlier interest are being emailed direct.  Whoever wants one, please
> email me direct.
>
> 73,
>
> Bill, K3PGB
>
>
73, Jerry, Technical Adviser to the Collins Radio Association.