Bad Choke?

[Diablo]

I think I have a bad choke. Symptoms are black lead to mounting lug - 4 ohms. White lead to mounting lug - 157 ohms. Can anyone verify that a choke shouldn't have one lead grounded internally to the mounting lug? Or is this some new design to give me a big headache?

[Enzo]

A choke most definitely doesn;t short to frame on purpose. it is a series element of your B+ filter after all.

[Diablo]

Thanks Enzo. Now I can sleep better since I found the problem. I was powering up a new build with a Variac, and when I got to around 90V AC, the fuse popped. I hope I didn't damage the PT. I should have checked the choke resistance before installation - now I know better for next time.

[Enzo]

What you need to do is add an AC ammeter in series with the amp as you bring up the variac. Your DMM probably has AC amps as a function. You can even remove the amp main fuse and clip the meter in its place.

Now as you start bringing up the variac, you can see the current going up up up, and you then know to back off. No reason to turn it up enough to blow fuses. if the current remains at a reasonable level you can continue to raise the voltage.