[Penthode]

Curious: I had exactly the same failure on the red static convergence pot on my CTC5. There was a crack about a half way along the low resistance element end.

I do not think the pot suffered from electrical stress. I think the problem was with manufacturing and shrinkage of the carbon element over time. The break always seems to occur between the two rivets on the lower resistive portion to the tap simply because there are physically close together.

This evening I tried my fix: I went to "Canadian Tire" and picked up a rear window defroster repair kit. The kit includes conductive paint. I cleaned the pot element where the break occurred and painted a narrow band right over the crack.

After the paint dried, I reassembled the pot and it seemed to work fine. I checked the resistance of the previously broken section and it now measured 35 ohms, which is slightly low but about right. I then reinstalled the pot in the set and the static convergence adjustment now works okay.

Overall, I like the static adjustment on the front panel. But the pots are a pain. The design isn't bad: even though the static convergence voltage is derived from horizontal output plate current, any variations in current are mostly compensated for so that the convergence does not vary. It's just those bad pots. I would be just as happy to substitute the convergence clover leaf assembly with one which has permanent magnet adjustment, but that would be non-original.

I suspect the repaired pot should last a while until I can think of a better solution.