Collins transfomer connections

[N0WEK]

Did Collins use a standard connection scheme on their transformers?

I've got a pair of transformers out of some piece of gear, (part # 672-2680-00) 105-125 vac primary/550-ct-550 secondary along with a 5 vac ct transformer for the rectifier.

All the have are numbers 1-9 on the plate transformer and similar on the filament transformer.

I can probably figure it out but thought I'd ask first.

Greg

[KE6DF]

I've never had much luck finding info from these OEM part numbers.

With 9 terminals a guess would be: 

Two 115 primaries designed to be connected in parallel for 115v operation or in series for 230V.

There might be a tap on each for say 105 V.

A lot of CG type UTC transformers are that way.

That accounts for 6 terminals.

That leaves three pins for the center tapped secondaries.

Sounds like it's time to get out the ohm meter. And then try putting 5 vac into one winding and measuring what you get from the others.

[N0WEK]

It turns out that there are 10 terminals. #1 seems to be primary common except that #2 is only about 10 volts off of #1; after that seems to be #3-#7 seem to be the 105-125 vac taps. #8 and #10 are the 550 volt hots with #9 being the center tap. I can see a slag mark where someone tried to hook up to #1 and #2 with 120 vac.

I ran it up on a variac to #1 and #7 and got the expected 550 vac each side of the CT. I didn't have anything to load it down with.

The filament transformer runs just fine with power on #1 and #6 (125 vac tap) and it checks out with 5 vct on #7 and #9 with #8  being the CT.

Everything seems to make sense except that weird tap that's only 10 volts off the common on the plate transformer.

Any ideas?

Greg

[KE6DF]

Well they may have added that 10 v tap to give you more primary choices.

So if you have a bunch of taps from 105 to 125, by using the 10v tap you would add 95 and 100v to your list of choices (the others overlap). You get two more voltage choices with only one more pin.

I've seen that done on other transformers.

In any case, having lots of primary taps is a nice feature -- particularly on a filament transformer as once you get it under load with the filaments of the tubes you are going to use you can try different primary taps until you get the voltage right.

My local line voltage is 123 - 124vac. That's too high for most old transformers. Doesn't usually matter that much on plate transformers, but on filamants you don't want to run filaments 7% too high with a 115v transformer. That 125v tap would come in handy.

Dave