Salvaged Power transformer problem

[Tapsnap]

This is a transformer that I pulled from a TV from 1948. I wanted to find what I had for voltages on the secondary, so I connected the heavy white wires to the AC. The circuit breaker snapped off the power. It shorted. I took the bell off to inspect the inside to see if the wires were perished, but they seemed fine. I am curious to know what you think. Is this transformer cooked or can it be fixed?

[DummyLoad]

respectfully, that was quite a moronic stunt! do you have video? 


--pete

[Tapsnap]

Care to explain?

[sluckey]

Those heavy white wires are likely a filament winding. Probably only measures about zero ohms. You may want to repeat that experiment but this time assume the black wires are the primary. And use a variac to bring the voltage up slowly. Got no variac? Then use a lightbulb limiter.

[Tapsnap]

Ok, well luckily I didn’t fry it. The black wires are, in fact, the primary wires. The high voltage measures 675v, the green measures 5.86v, the white 5.96v and the yellow 4.69v.

[sluckey]

The high voltage measures 675v, the green measures 5.86v, the white 5.96v and the yellow 4.69v.

Are those readings with the black wires plugged straight into the wall?

[Tapsnap]

No, those are readings through a light bulb in series.

[sluckey]

Voltages will be low when using the bulb limiter. Plug it straight into the wall to see what the voltages really are.

[Tapsnap]

Without the bulb limiter, I get 395v from the center tap to each leg of the HV.My meter doesn’t go beyond 700vac. The yellow reads 5.3v, the green reads 6.6v and the white is 6.6v also.

[sluckey]

OK. While it's fresh on your mind, twist the different colored wires together, put a piece of masking tape on each group, and write the measured voltages on each piece of tape. Set it on the shelf and wait for an appropriate project to come along. Gonna be big tubes. No EL84 or 6V6 projects.

[Tapsnap]

OK, thanks for your help.

[DummyLoad]

your transformer would be adequate to build a supply for a pair of KT88/6550 in UL for 100W. should make about 500-525V loaded. perhaps a sunn sorado or a twin plan with KT88/6550?


--pete

[Tapsnap]

Could I use that heavy 6.6v secondary to make a bias voltage?
I have a RadioShack 120v to 12.6v transformer. If I reverse the input that would produce 60 volts or so. Is this a dumb idea also?

[sluckey]

That will work. But it's much simpler to feed the bias circuit from one of the HT wires, like Marshall Plexi style.

[Tapsnap]

I haven’t really studied the circuits of these large amps. So far I’ve built just 3 amps, all under 20w