The Chemicals that Made American Signaling Great

Two months before ALTO Tower closed I went out for a final round of photos on a sunny spring day and while I was there I spent some time at the satellite interlocking CP-SLOPE, which was under direct wire control from ALTO tower.  The old SLOPE tower was closed in the 1950's with a relay plant being constructed on the foundation.  However the power supply for the interlocking remained much as it was when the tower was open.  Pole line power is nothing new in my experience, however the PRR was not about to be satisfied with some dinky 440 volt wires on a telegraph pole and SLOPE was fed from ALTO through a thick bundle of signal wires to a number of vintage 1930's or 1940's "Pole Pig" at the westbound signal gantry.

 Hmmm, what's that sticker on the side of the transformer.  Let's take a closer look.

Yup, good old PCB's.  Except no substitutes when cooling a transformer.  In what could be the ultimate example of "if it ain't broke" this power supply lasted past the closing of the tower, past the formation of the Penn Central and Conrail and right up to the point that ALTO itself was closed and eliminated with those persistent organic pollutants staying stable, year in, year out.  This wasn't the only example either.  There were two more at the SLOPE relay plant.

I have asked around, but have not been able to definitively date these transformers except that they probably date from the 30's or 40's.  Help would be appreciated.