The AM Forum

Found an August 1937 QST schematic showing special center tapped equalizing chokes for putting MV rectifiers in parallel.

The type given is a UTC PA-11B.  Its interesting because most of the 'ham' books show 50-100 Ohm resistors in series with the individual tubes' anodes used for the paralleling purpose.

The chokes would tend to force the currents to be divided equally between two tubes. The B+ output is 1300VDC. The plate transformer is the PA-119 rated 1500-0-1500V at 1 Amp.

The reason given for using the chokes is to avoid the more expensive 872 rectifiers. Its interesting that at some point a special choke was so inexpensive that it offset the cost difference between two 866s and one 872. The practice of using equalizing chokes seems to have been short-lived in amateur service.

The UTC PA series xfmrs and chokes predated the UTC S series.  The PA series is far better than the later S series.  I have a few PA chokes, some of the best I ever tested.

Fred

That topology was common in big, 3-phase power MV supplies found in TX and RF gens.

That combined with quadrature filaments gave the most lifespan out of MV tubes.

73DG

Don't forget the CG series. They are apparently the same products electrically, some PA and some CG. The example would be the CG-309 and PA-309 plate transformers. The difference on this part looks like a packaging difference with the PA-309 more squat and CG-309 taller and thinner. Might be a weight reduction or cost cut on the end bells. Another product the PA-512 driver transformer, is just like the CG-512.

Was the quadrature filament current obtained via the 3-phase arrangement or was it a result of added inductors?

Quad fils were done where each tube had it's fil linked to that rectifying phase, inphase.

Used a lot more fil iron, but back then, iron was cheap, the tubes were not.

Well explained in later RCA TX tube handbooks.

73DG

I'll have to look it up. I did not find the chokes in the catalogs yet.