My CT-100 lost HV (from losing one B+ line).

[ohohyodafarted]

I have had similar B+ problems in sets where the insulation is starting to break down inside the candohm resistor riveted to the back of the chassis. Typically the insulation will break down and a spark will jump between ground and the resistance element inside the candohm. It will blow the fuse if there is one. Sometimes you can put a new fuse in and the set will operate again until another spark jumps and blows the fuse again.

If you get lucky a carbon trail will form inside the candohm and cause a constant arcing failure, and than you can narrow it down to a defective candohm. I guess you also might be able to disconnect the leads and measure the resistance between ground and the candohm terminals. I would think a good candohm would have megohmss of resistance from the lugs to ground. Perhaps someone else here might be able to give us a better idea of how much isolation resistance you would find in a good candohm versus a bad one.

And like someone else here said, you could also have tin wiskers in a control pot. But when I have had a pot arc, the arc usually wiped out the pot.

Keep that 200ma fuse in the set and if it blows again, perhaps it will help reveal which part is arcing. I do not believe the arc/snap sound you heard would come from a fuse. When you hear a loud snap/crack sound and the B+ goes out, you likely have a component that arced to ground. I have even had one occasion where, there was a lead on a B+ filter cap terminal that was too close to ground and arced over. Replacing the fuse and watching under the chassis in the dark for the arc to happen again revealed where the arc occurred.

[dtvmcdonald]

Originally Posted by ohohyodafarted

I have had similar B+ problems in sets where the insulation is starting to break down inside the candohm resistor riveted to the back of the chassis.

One side of that Candohm is at -20 volts to ground, the other
at -10 volts to ground. The only fuse it could blow is the one in the
B+ line to the horizontal output transformer, by reducing (to -10 volts)
the fixed grid bias on the horizontal output tube ... which will even then
get bias from the drive waveform. If it were to open, it would just
just ruin the vertical centering and slightly raise (to a higher negative
voltage) that fixed grid bias.