Hastings VT-4B Replacement Transformer

We have a Hastings VT-4B made by Beede Electronic Instruments Co, Inc. The line transformer in this unit has burned. It's a custom transformer, made by Regional Mfg. Specialists, part number 528214-G. From what I can tell, it just feeds into a bridge, center tap grounded, which powers the LM78L12 & L79L12 regulators. Dimentions on it are 1.635in x 1.325in x 1.325in. It has wire leads, no terminals, and is mounted by two screws through the cores. Any suggestions for replacement? Would a 12.6-0-12.6 transformer give enough headroom for the regulators?

Thanks, Steve

Reply to
sck0006
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The electroncs draw very little power so it might be OK. 12.6 * 1.4 (peak) is about 17.6 V, But, you need 1.4 V or so for the bridge, another 2? V for the regulator, and something for ripple, so that's getting close to the required

12 VDC output, especially over the allowed line voltage range.

I'd probably go with 14 VRMS or so if there is a standard part you can fit in there.

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Reply to
Sam Goldwasser

Thanks for the reply Sam, always apprecaited. The only thing I could find with the right dimensions in a hurry was a Hammond 266C24. I guess we'll just wait unitl it gets here and see. I believe I'm going to have to rip off the chassis mount part and drill through the cores, but maybe I'll get a little lucky.

Thanks again, Steve

Reply to
Steve

Don't drill anything. Use hot melt glue or nylon ties to secure it. :)

If it turns out to be marginal, maybe replace the regulator with a low dropout equivalent.

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Reply to
Sam Goldwasser

Ok, we got the transformer in, physically it is smaller than the other, mounting it shouldn't be a problem. Without a vacuum tube plugged in, the regulators maintain regulation down to 100VAC line voltage. Now I want to load it to make sure it does in fact have enough headroom and that the transformer won't overheat. What sort of load do these tubes impose on the circuit?

Thanks, Steve

Reply to
Steve

Not much. For the DV-4D tube used with the VT-4, the heater current is

29 mA at 320 mV, about 9 mW. So put a 10 ohm resistor between pins 3 and 5 of the octal socket but the power supply won't even notice.

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Reply to
Sam Goldwasser

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I guess it's just the light load on the transformer, but a little

12-0-12VCT transformer rated at .085A has no problem giving the regulators plenty of extra room. At 105VAC line voltage with the circuit loaded, the filter caps have ~16VDC on them, plenty of room for a 12V regulator. There is only ~20mA draw on each leg of the transformer, so it should be happy. Thanks for the help, Steve
Reply to
sck0006

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