|
Lots of good suggestions here -- thanks!
A little history on my coil: After I first restored my Hallicrafters 505, I noticed the HV fade problem. At that time, I found that baking the coil fixed it -- termporarily. After a week or two, it would reabsorb moisture and the problem came back.
To try to give it a more permanent fix, I washed it, baked it for a long time, and then coated with multiple coats of varnish. This kept it alive for a while, but after a month or so it was back to the same. This didn't really surprise me too much, since all polymer coatings (varnish, epoxy, etc.) are permeable to water. None of these kinds of coatings really seal out water.
After reading various related discussions here and on ARF, I've been trying to boost the drive circuit a bit and see if that can solve the problem. It already is doing pretty well right now -- I can run it for about an hour before the picture starts to bloom. However, it is very tricky to tell whether the improvement is due to my work, or just the fact that running it repeatedly over a number of days has the effect of baking the moisture out. So not clear how it will be a week or a month from now.
I also picked up a nice little muffin fan at Radio Shack which I will mount in the HV cage, since it is clear that air flow helps. With the lid on the HV cage, it fades faster than with the lid off.
What surprises me is that even after HV has faded, the coil is barely warm to the touch. It's certainly not as though the thing is really heating up.
I'll try a little more work on the circuitry, and also the fan and see where things stand. I'll also look into picking up one of the various HV modules mentioned above in case that is needed.
Tom
|