I don't know if this is exactly where this belongs, but the fixture in question was made in 1977, so at least that fits here.

I have a backlit Pepsi wall clock which uses 2 f8t5 lamps. They are in a simple pre-heat configuration with simple "choke" type ballasts.

A while back, I replaced both lamps because one of them had failed, about 2 months later the one which failed went out again, but this time wasn't showing any life, not even attempting to strike. Upon opening the clock, I first tried replacing the starter, which did nothing. Then I switched the two lamps around, and the "good" lamp instantly got blown up. I took both ballasts out and measured their resistance, the working one measured around 70 ohms, where the failed one measured around 12 ohms. I then cut the paper off of the windings, and they were burned and black, so it got HOT.

I am wondering why this would have happened though; I have owned and do own hundreds of these small choke type ballasts, and have never seen a failed one like this. I have seen one which was open, and a bunch which were buzzy, but I have never seen one just baked like this one was.

It didn't run for an extended period of time with the EOL lamp in it, maybe 15 minutes while I was moving stuff to pull it off of the wall, probably less than that. The only abnormality (if you even want to call it that) is that it was running FS-2 starters instead of FS-5 starters, which are technically what it calls for. It never had any issues starting though, and the non-failed ballast had the same starter on it. Would using an FS-2 in place of an FS-5 cause damage?

My other theory is about General Electric. The ballasts are presumably original to the clock, which is from 1977. I also collect fans, and around that time GE was having issues with the windings in their fan motors failing, shorting, and burning. Something about a mix of copper and aluminum windings. I am wondering if maybe that same defect affected other things like transformers and ballasts since motor windings and transformer windings aren't really too much different.

Of course, I suppose it could have somehow failed just due to age, but I really don't understand how, it is a simple coil of wire. No capacitors, or any electronics or moving parts. Windings shouldn't just short on their own.

A brief run with EOL lamp of course should not kill a choke. But remember these are are almost 50 years old. Insulation lacquer  on the wire is getting oxidized over time, so it loses both electrical and mechanical strength. A little abuse by a constant preheat and series of high voltage pulses as starter clicks may be enough... Old transformers and chokes DO fail sometimes.

Once a single short circuit between a couple of turns happens in the winding it quickly propagates to the neighbors due to high local current and overheating, until the whole choke is almost completely shorted, as you see in the end result...

   

As far as I understand, another factor that could destroy a magnetic choke ballast is an excessive line voltage which can cause the ballast to run at overcurrent. The overcurrent causes the ballast to heat up, which eventually causes the insulation on the windings to break down and eventually causes the windings to possibly short out with each other or the core.

It certainly isn't caused by excessive line voltage. On a good day the voltage is around 118 or so in the back room where it is; but it is normally closer to 110.