Old Dual-Pro type dual OT

[EFK]

Can someone definitively explain to me how the two output transformers on an old late 1940s Fender dual pro would be installed? As I understand it, each OT was mounted on the speaker (2 speakers) so the secondary aspect seems pretty clear. Where I'm confused is hgow the primaries were hooked up to two tubes? If the B+ went to both center taps, and the primaries were simply paralleled, wouldn;t the reflected impedance to the two tubes be half of each OT primary? In other words, if you wanted a total 6K reflected to the two tubes, and you were paralleling the two transformers, would you then need two 12K transformers? Or if you were running them in series, you'd need two 3K transfomers, correct?

Hopefully someone can let me know if I'm understanding this correctly.

[Bruce / Mission Amps]

I also thought the primaries of these two OTs in the amps were in parallel and in phase... so it was just like as if you put two batteries in parallel and phase or two power transformers in parallel and in phase... etc.
I've never measured the Zed of these... but because of their size, I would not be surprised to find out they were 8K to 12K OTs each.

[Steve Conner]

In other words, if you wanted a total 6K reflected to the two tubes, and you were paralleling the two transformers, would you then need two 12K transformers?

Yup!

Or if you were running them in series, you'd need two 3K transfomers, correct?

I can't think how you would connect two push-pull OTs in series.

[EFK]

Thanks guys. I think this clears it up a little for me. So I understand paralleling them, at least on the primary side of it. And the secondaries of each run their own speaker. Are there any considerations for the secondary side of it? Say, two 8K in parallel for a 4K reflected, each with 8 ohm secondaries. Each secondary is running it's own 8 ohm speaker. Is it really that simple? Or is there some kind of parallel thing going on with the speakers and/or secondary load also?

Steve I thought I remember seeing some kind of diagram of OT being run in series somewhere, but since you mention it, I guess they must have been single ended because now that I think on it, I don't see how pp OT could be run in series either!