Power Transformer lights up dim bulb

[tdlunsfo]

I haven't been doing this long enough to have seen something like this yet but I am still curious as to the failure. Thoughts on this? Transformer ohms out as such:
Pri: 5.5 ohm
Sec: 256 ohm
Fil: .5 ohm
This is from a Epi Elektar reissue. Transformer is a wuxi juke??
Result =

[The Dude]

Have you checked for shorts between windings? Maybe primary to secondary is shorted or one secondary winding to another. Since you already have it hooked up, what voltages do you get out of the secondary? If the bulb is bright, I'm guessing there is a short somewhere. Of course, watch your fingers!

[mac dillard]

give this a shot::https://www.premierguitar.com/articl...ormer-tester-1

[tdlunsfo]

That's what threw me at first. Everything appears to ohm out okay and no shorts between windings or to the transformer chassis, but sure enough it lights up that 100W bulb like christmas. I did a quick voltage measurement with it on the dim bulb and the secondary was 1.5V and the filament around 500mv. Do you think it is safe to take measurements off of the dim bulb? I've never been down this road and don't really want to see one of these melt down in front me.

[tdlunsfo]

Interesting test with the neon bulb. Will need to find me a bulb but will try it out.

[Jazz P Bass]

Do not attempt to power up that transformer without the limiter..
If you do, fuse the mains line.

The transformer is bad if it illuminates a 100 watt lamp like that.

[Enzo]

Your meter can only do the grossest of tests. Would you know if that 256 ohms ought to be 258 ohms? No. Windings rarely short end to end, but turn to turn is way more common, and your meter would never know. Also failed insulation in the windings could allow an arc to form at voltage, but your meter only uses a volt or two, so it never shows up in tests.

[Helmholtz]

I would feed heater voltage from another amp to the heater winding of the PT and measure voltage across primary.