Unusual power transformer

[CharlesASD]

One way or another I ended up with this transformer, and I am confused by its windings. I know it came out of a tube amp, possibly a Heathkit, but didn't see how it was hooked up. I might even be wrong in thinking that it is a power transformer, ha.
A bridge rectifier gives me way too much voltage, but a two-phase would be about right, except of course that the transformer dosn't have a center tap. I have made an artificial center tap for a heater transformer with two 220ohm resistors before, but with this situation that would waste a lot of current, right?
If an artificial ground is the right way to go, how large of a resistor can I use? Is there another device or scheme that would be more appropriate?
Mostly I am just puzzled by what this transformer is supposed to be used for. I might be going in the wrong direction. Thanks for any help!

 

[scott2000]

The couple of Heathkit power transformers I've seen were usually used as voltage doublers with an ac heater supply.....  I think the green wires were for the heaters iirc......

Got any pictures or numbers????

Kind of messing around with some dangerous voltages there......  :-\

 

[CharlesASD]

Here is a photo... google hasn't had any hits for the model numbers, but maybe there are other search terms that would help exclude movies about giant robots....

 

[CharlesASD]

Heathkit aa-181's power transformer has a smaller chunk of windings in the middle of the B+ windings. Not centered, though.
I wonder if this mystery transformer was supposed to have the center winding overlapping one of the B+ windings (with one of the 7.32v taps being the center tap for the B+), but the winding was small enough and the tolerances loose enough that now both B+ windings are equal.
This would kill my center ground for AC heaters though, and might not have enough to make DC heaters. I'll try loading it, and see how much sag there is. Might just have to get a separate transformer for the heaters....

 

[CJ]

do not hook that winding up to a tube heater, you might cook it in a hurry,

that is probably #32 wire in there, good for about  60 to 100 ma,  a tube will want a lot more than that.

that is a neg bias supply coming off that tap.

 

[scott2000]

The model number is stamped on the top ? Here is a decent reference for what some models had used....

http://www.nostalgickitscentral.com/heath/xfmrlist.html

And here's what I've seen them wired like..... doesn't look like yours

I would not just randomly try hooking things up.

 

[trobbins]

So lets assume the 7.3V is for heaters, given those voltages were unloaded measurements and meant for 117VAC primary.

If a 25+25 ohm humdinger was used for 0V ground, and a valve full-wave rectifier was used for a lowish powered amp or equipment (given the transformer core size looks smallish), then each diode current pulse may peak at about 200mApk.  The humdinger already has about 200mApk flowing through it near the peak of the heater voltage waveform, so an extra 200mApk is going to increase one side of the humdinger from circa 5Vpk to nearly 10Vpk, and so the heater mid-point will have a 5Vpk 100Hz signal on it.

Given it has a valve rectifier, and the B+ filtering could be minimal, the AC signal on the humdinger mid-point would an improvement on grounding one end of the heater (a not uncommon practise).

Whether that resulted in an economic benefit, given the likely wire-size change - dunno.

 

[CharlesASD]

Thanks for all of the replies.
"68PO28-4" are the only markings I can find, even with the bell ends off.
It does seem to be a tap for bias. I'm slowly learning! Now I just need to make something pretty with it....
Thanks again!