Hammond 1626 O/T

[Furtz]

I want to use a Hammond 1626 O/T in my Tweed Pro style build. It came from a similar donor amp. The secondary has two separate windings with black/white and green/brown leads. I want to connect it for an 8ohm load. Hammond doesn't have any hook-up diagrams for this particular O/T, or any other with two windings and these lead colors.
Any ideas or info would be more than welcomed.
Thanks in advance.

[David Root]

It does not appear to exist! Must be an obsolete design. Has two separate output windings, maybe from an old "stereo" organ amp?

I would connect the two windings in parallel and put 20-30V AC from a Variac into the primary and measure the AC voltage from the secondary. Take both voltages, square them and divide the secondary voltage squared by 8. Call the primary impedance Zaa.

Then (Vpri)squared/Zaa=(Vsec) squared/8

Solve for Zaa. This ignores losses but is close enough for rock 'n roll.

If the Zaa for 8 ohms secondary doesn't work for the tubes/voltages you want to use you will have to reevaluate your secondary impedance selection.

I think I got that right.

[Furtz]

Thanks for that David. I will do the calculations in the next few days. I'll do it with the secondaries in parallel, in series, and separately. I got this transformer out of a really poorly built Bassman/Bassmaster copy. It was originally hooked up with just the black and white leads for an 8ohm load, but judging how the amp was put together, I have no faith that it was correct.
Hope you have a great new year. I hear it's pretty cold out there.

[David Root]

Yes it is, but nice and sunny though!

[Furtz]

Hey David. May I pick your brain again?
I did the calculation and it works out to a 6k reflected impedance with an 8 ohm load. The two secondary windings are the same. Would there be any advantage or disadvantage to paralleling them?

[David Root]

Double the power handling capability. My guess is that's how they were originally connected. Back in those days about 6K was considered OK for a pair of 6L6.

NOT 6L6GC though. If that's what you're going to use you need 4K, and bigger PT and OT.

Which tweed Pro schematic are you using? 5C5, 5D5, 5E5? They all use 6L6 or 6L6WGB (5E5).

[Furtz]

Maybe I should have said Tweedish. It's cathode biased with 2K screen resistors. I'm getting 383V plate to cathode and 375V screen to cathode. I'm using a new pair of JJ 6L6GCs. With an Amp-Head Dual Bias Tester, I'm getting a 36mA reading.
Should I connect the secondaries in series to get the impedance down to 3K ?