I have four F40T12 rapid-start tubes that are all dead. Three of them have one open cathode and one of them has both cathodes open. Any way to get some fun out of these? I believe they all have maintained their gas fill.

I haven't seen anything on here but maybe I haven't looked hard enough

Thanks!
 

Are these mechanically broken or really EOL with large black 'socks' at the ends?

Lamps with mechanically broken cathodes can be reused on instant start ballast, ones that are truly EOL better be let RIP in recycling. Until some really collectable. May be some tesla coil experiments so electrodeless use...

The one with 2 broken cathodes is mechanically broken, the other 3 are EOL.

I have successfully powered up a few dead T12 bulb with large socks and open cathodes on a homemade high frequency fluorescent tube inverter. They can’t be used at full brightness, but they do work at about 50% brightness. But that’s a limitation of my homemade HF inverter. It works by making a really high voltage that just strikes the tubes without any preheating of the kathodes. It’s extremely mean and causes dark ends fast, not recommended to use with working tubes but it does allow using dead tubes! Which is really cool. I ran a couple F40T12’s that were dead for a whole day on this inverter and they worked fine, 50% brightness but they sure worked! And I bet I could get an insane amount of hours out of them by using this method since there’s no need for intact kathodes. The arc will jump from the support structure of the kathodes just fine! But you can’t run them at full power or what little isurface area there is remaining will just glow red and it’ll eventually crack at the ends.

I have seen other collectors would try to run them on instant start electronic fluorescent ballasts and overdrive them until they lose vacuum.

Which is of course a rather stupid thing to do...

I have successfully powered up a few dead T12 bulb with large socks and open cathodes on a homemade high frequency fluorescent tube inverter. They can’t be used at full brightness, but they do work at about 50% brightness. But that’s a limitation of my homemade HF inverter. It works by making a really high voltage that just strikes the tubes without any preheating of the kathodes. It’s extremely mean and causes dark ends fast, not recommended to use with working tubes but it does allow using dead tubes! Which is really cool. I ran a couple F40T12’s that were dead for a whole day on this inverter and they worked fine, 50% brightness but they sure worked! And I bet I could get an insane amount of hours out of them by using this method since there’s no need for intact kathodes. The arc will jump from the support structure of the kathodes just fine! But you can’t run them at full power or what little isurface area there is remaining will just glow red and it’ll eventually crack at the ends.

No this just will not work at full and even at 50% current. Arc can not be run off electrode supports for any significant time before melting them. Have you measured the current REALLY before bragging about getting 50% of brightness? One can get some tens of milliamps of glow discharge, but this is not much light and the lamp will quickly die off from sputtering, anyway...

I don’t know how bright they really are but it works power draw around 20 watts including inverter losses, so maybe 15 watts going to the tube.. And I’ve ran them like that for at least half a day, so it seems to last a while at least. The best thing to do is probably just to accept that the tube is dead and then recycle it unless it’s an extreme rarity tbh , I haven’t tested how long it’ll last, and I threw away my dead tubes because they weren’t anything special and I have plenty of new ones to enjoy in my proper lights

Try operating them the MH way . Once I had a burned out T12 tube that had one cathode broken and I wanted to run it since it was my first T12 lamp with an inner blue phosphor coating <<not any rare lamp, just a Chinese non branded bug lamp made in 2019>>. So, being inspired by MH lamps and their way of using 2 terminals to create an arc, I wired my 20w tube with an ignitor and it's ballast. It worked great and was running for more than 5 hours with no issues until I got bored of it and switched it off. So yea, you can try this method if you like, for me it worked great. 

This would probably work, but I am in the US where superimposed ignitors aren’t very accessible, and even if I did get one I would have to use a special 240V 60Hz ballast with it for it to work. But, I believe if I got a 35W pulse-start metal halide autotransformer ballast, that would probably work.

I just light them up on an electronic instant-start ballast & fry them. (and video it) .lol.
A bit of fun before throwing them away.

If only one filament is burned out, they can be ran on a LPF 2-lamp magnetic RS ballast. (will light around 50% brightness, and can last a long time .. there's some EOL F40's that've been in my garage fixtures for years like that (infact wouldn't be surprized if some of those have been there for a decade or more))

But beware that deliberately running rectifying lamps can potentially fry some RS circuits. They *should* made to be able to withstand this, but why trying to check )

@RRK:
Yep. True.
Though any magnetic 2xF40 or 2xF20 LPF RS ballast I've come across does just fine (infact it runs quit a bit cooler than normal).
...Now 1-lamp LPF RS ballasts, different story. Those will overheat & shut down with an EOL lamp.