I have for sale: 2 machine/industrial control transformers rated for 1.5KVA(1500VA) made by Westinghouse, have a different core disign than usal...They have two windings on one side, and a single on the other I think designed for 220/440 to 220/110 depending on how you wire them up.
I have a couple of these too, but mine are rated at 150 va. About the size of your fist. Also made by Westinghouse.
Does anyone know exactly what these were intended to be used for?
I plucked one of mine out of the BTA-1R I parted out. Picked up the other one, new in the box, at Dayton. They make excellent transformers for brute force bias supplies for class-B modulators (and slopbucket leeenyars). You can set them up for 110 or 220v each side of midtap, and easily pull 500 ma of bleeder current using a few hundred ohms of wirewound rheostat or slidetap resistor to pick off the appropriate bias voltage. The class-B grid current is a small enough percentage of the total bleeder load on the bias supply, that good regulation is maintained without resorting to electronic voltage regulation.
My HF-300 rig uses a pair of 5Z3's for rectifiers. Of course, this circuit lends itself very well to solid state rectifiers, since you don't need diodes with very much peak inverse voltage rating in this application.
Why not use electronic regulation and a lighter weight voltage supply? The problem I had with mine was due to a.c. line voltage variation. The bias voltage remained fixed by the regulator, but the modulator plate voltage varied with the line voltage. The modulator tubes effectively amplify the relative difference between bias and plate voltage, so that with a slight change in line voltage, the resting plate current varies big time, and I found myself constantly fiddling with the bias control to maintain the proper value. With a simple brute-force supply, the static plate current varies at about the same percentage as the modulator plate voltage, which is the way it should be.
The reason this works is that when the line voltage drops, the plate voltage drops, but so does the bias voltage at the same percentage, causing less drop in static place current.
You may have noticed that most tube-type broadcast transmitters use this simple bias supply circuit instead of electronic regulation. These transformers are a real find for this applacation, since low voltage, high current plate transformers are very rare. UTC and a couple other companies made such transformers specifically for bias supply applications, but these have become extremely rare and hard to find. Industrial control transformers seem to be plentiful.