I'm trying to figure out what is up with my one & only 8' slimline fixture. It has a low-quality Radionic magnetic series-sequence ballast (that it came with) and modern GE lamps (which were made by Philips). One lamp operates normally, the other is dim and looks like it's rectifying if the ambient temperature is below about room temperature.

If I switch the lamps to opposite sockets, it works fine for some hours but soon goes back to doing the same. So the issue is on one side.

I changed the lamps out because the Sylvania /CWX lamps would pulsate when cold and never stop. They used to work fine after warm up. They were always too dim and pink in my opinion though. I have searched for years and cannot find any old-stock 96" lamps to try, or I would in a heartbeat - so I've been stuck with what they have at Lowe's.

Does it sounds like the ballast is failing, or do I just have low-quality lamps?

I will try getting a new ballast and see if things improve...I'd love to use a lead-lag ballast, but those won't fit in this fixture.

By slimline you mean single pin Instant Start tubes ?

Single pin tubes can heat the cathode filament only by the current that goes through it from the discharge, so the cathode temperature depends on the discharge current. Too low current will lead to a cold cathode, and a cold cathode is not effective at providing current (it also sputters)

The lamp arc voltage and restrike characteristics depend to some extent on the temperature. I guess at colder ambient temp, the restrike after zero crossing becomes harder. This combined with underpowered cathodes might get exactly to the area where one cathode is still just about hot enough, and one isn't, and the lamp doesn't restrike in this polarity



If the problem stays with the ballast side and not with the lamp when the lamps are swapped, then the problem is in the ballast. If there is a failed internal capacitor, that may be the problem - Allthough if it is in series with the lamp, it shouldn't be able to light while rectifying... (As this will charge the capacitor up until there is no sufficient voltage across the lamp) ?

Thanks, Ash...I think you are right. I ordered a NOS Advance ballast...I suspect the capacitor in this one is failing but maybe not failed yet? It's not a good brand to begin with.

These are single-pin lamps, yes. I think I probably will take the whole fixture down as it's chain-hung and easier to work on on the bench, then I can run some tests on it and see what's going on.

I took the fixture down and tried various lamps - same issue, always on one side. Changed the ballast - both lamps much brighter and equal in brightness. The old ballast was not even drawing 140VA with 75w lamps.

So I am guessing a failing capacitor (its an HPF ballast). I have experienced a lot of capacitor failures in electronics and lighting over the last couple of decades. The “new” ballast was dated 1989 so hopefully firing it up after all this time doesn’t lead to another soon-dead capacitor.

I have a 8' slimline in the garage where most of the time one lamp lights @ not quite full brightness, the other doesn't light or is real dim... but it will occasionally light, when it does the other will be full brightness.

Like yours, I assume the old ballast is probably shot. (doesn't matter what lamps I use, it does the same with any (surprisingly its its slightly more likely to work right with a 60w lamp on the 'bad' side))