[Joeztech]

For some time I have wished I had a utility tube type power supply to use in testing vintage radios. I recently found a nice old military type power transformer that I used to power a modified BC-348 receiver many years ago. it is a rather hefty unit that is 3in. X 3.5in. X 6in. and weighs about 6Lbs. It is hermetically sealed and has a total of 10 round ceramic insulated terminals with solder slots on the bottom along with 8-32 3/8in. mounting studs on it.

I did connect to 122VAC and here are the voltages I measured:

Measuring Instrument = Fluke 8600A digital multimeter recently calibrated.
Terminal Definitions:
1 – 2 = AC primary, 4.48 ohms DC resistance
3 - 4 – 5 = HV secondary, 3 - 4 = 96.8 ohms, 4 - 5 = 103.7 ohms, 3 - 5 = 200.5 ohms DC resistance
6 - 7 = 5VAC secondary, 0.13 ohms DC resistance
8 - 9 - 10 = 6.3VAC secondary, 8 - 10 = 0.14 ohms DC resistance
With 122VAC input these AC voltages were measured across secondary windings:
3 to 4 = 271VAC (4 is the center tap of the HV winding).
4 to 5 = 271VAC
3 to 5 = 544VAC
6 to 7 = 5.3VAC (probably a 2 amp capacity)
8 to 10 = 6.9VAC (probably a 5 to 6 amp capacity)
Looking at Chicago Transformer catalog information, the case style seems to be type B hermetically sealed and potted unit. There are two 1.125 in. indented circles on diagonal corners of the top of the case. I never did find any stamped part numbers or manufacturer & date code information on this transformer. There was no printed schematic of the transformer, although someone had scratched it in the paint on one side before I acquired it.

I have a 5AR4 rectifier tube and a 1.75H 200mA, 62 ohm choke and 500VDC rated electrolytics and some octal sockets on order to use with it. I have on hand some 4-pin and 5-pin sockets from Antique Electronic Supply. I can make the choke an item that can either be in circuit or out of circuit using banana jacks and plugs in case the radio I work on has a field core speaker. In those cases the field core will be the choke. The electrolytics can have an isolated plus and minus side so that a divider resistor can be used to provide the necessary negative bias for output stages if needed.

I should be able to get at least 270VDC from this or more depending on rectifier circuitry. I could use silicon rectifiers for higher voltage applications, perhaps a bridge arrangement and another set of electrolytics to handle even higher voltages if needed. I have a fair number of banana jacks and plugs on hand to use. I might find a suitable DC voltmeter to add to the chassis to monitor B+ while working on the radios.

There is room on the chassis I am using to add a Variac if desired. I need to find one of those. Our contributor, Brenda, sent me one that will handle up to 90 watts or so. I might want to go higher for more hungry radio chassis.

I am going to have to run some load tests of the B+ output to see just how much current it can handle safely. I do remember that using it with the BC-348 it never got really hot to touch. I had built a separate power supply and audio output stage using a 6AV6 and 6AQ5 at the time it was used with the BC-348.

I can also use the supply to breadboard experimental tube circuits. Lots of fun ahead!

Joe
KC5LY