Dagnall OT no wiring info

[Randall]

I got a new Dagnall D2512 / TXOP00012 OT for a Marshall JT30 that I think has a weak original. It came with no documentation. I have ID'd the HT side with 76 and 77 ohms from CT, also I did manage to find a drawing on a site in the UK that says the secondary is higher gauge wire, and that rings true. However, I am not sure about the secondary terminals. There are three, ground, 8 ohm, and 16 ohm, but I am not sure which side is ground and which is 16 ohm. Following the way the original is connected with ground on the left I see left to center = 0.7 ohms, and left to right = 0.9 ohms. Going in reverse I see right to center = 0.4 ohms, and from right to left I see 0.9 ohms.

The second way seems more correct to me, but it is opposite of the original, which makes me wonder if the original is wired wrong?

[nickb]

So left to center is 0.7 ohms and left to right is 0.9 ohms ( roughly ).

The DC resistance is proportional to the turns and the impedance to the square of the turns. Thus the 16 ohm winding will have sqrt(2) times the DC resistance of the 8 i.e 0.7 * 1.412 = 0.98. So my money is on: left = ground, middle= 8 and right = 16.

You would always connect left and right to the heater winding and check for 6.3/1.4 = 4.5V RMS on left to middle. Watch out for HV on the primary if you do test like this.

[Gregg]

This is supposed to be a drop in replacement so the sticker should give you an idea which terminal is which.

https://www.tube-town.net/ttstore/Tr...401::7808.html

Also check this out:

https://www.amplifiedparts.com/produ...put-30-w-jtm30

[Randall]

That's it! Thank you guys for both the technical and image responses. I feel confident now.