Vox Night Train (NT15H) OT resistance

[glebert]

Working on this NT15H, output very low and distorted. Doing a resistance measurements on the primary of the OT gives 13 ohms from one side to center and 106 ohms to the other, and then 119 from end to end. This was measured hooked up to the board, so that could be causing a low reading if there is a problem on the board. This difference in resistances seems suspect to me, what would be a "normal" resistance on an OT like this (EL-84 push pull, btw).

Thanks,
Greg

[Greg Robinson]

50-100ohms from plate to center tap would be typical. Sounds like the output transformer has shorted turns, probably run without a load for a while. Do a neon bulb test or a ratio test with a low voltage to confirm.

[g1]

I think if you get same readings with wires disconnected it is bad.