Troubleshooting An OT

[Daver]

I'm working on a stereo Twilighter (Magnatone). The amp has no tubes and hasn't been run in a while. I'm doing all the preflight checks and noticed something unusual with one of the output transformers. When measuring the primary DCR one of them is about 290 ohms per side. The other is about 290 ohms on one side and nearly 1K on the other. There are no shorts to the secondary. Is this an indication that it's bad? I've measured shorted OT's where you'd get 0 ohms or close to it or blown ones with near infinity. Should I fire it up and see or replace it first? Thanks.
Dave

[52 Bill]

Seeing as you have one side of the primary reading 4 times the dc ohms as the other side and the other transformer reading a fairly even 290 ohms, it would appear that there is problem with the transformer.

You can power it up, but I would expect the tube on the side of the transformer that reads 1k will not be working correctly. Read the voltage to the plates and see how far off the one side is.

[techineer]

Here are a couple of tests you can make:

Shorts test: Connect a neon lamp (NE-2 or similar with a series resistor - 47K typical) across the primary leads. Plug a pigtail test cable into the speaker jack and touch the free ends across a 1.5V 'D' cell. If there are no shorted turns, the lamp should flash every time the battery connection is broken.

Reverse Signal test - Use a signal generator to feed about 1VRMS at about 200 HZ into the speaker jack. Use an AC voltmeter or oscilloscope (preferred) to observe the voltage across each half of the primary. (Center tap to ends.) They should be approximately equal, and if the generator isn't overloaded, they should be without significant distortion.

[Daver]

Thanks, techineer, I'll give those tests a try.
Dave