That's pretty awesome finding a bunch of bi-pin instant start F40s. if I'm not mistaken, these vintage 2 lamp instant start fixtures intentionally used medium bi-pin sockets with the line hot connected to one socket, line neutral to the other socket, and ballast input leads wired to that same socket, and instant start lamps, which are basically a standard F40 with internally shunted end caps, to act as a switch to disconnect power to the primary coil of the ballast when either lamp is removed, to protect a worker against receiving a high voltage shock and possibly falling off a ladder when changing a lamp. More modern magnetic ballast instant start fixtures use single pin lamps and are wired the same way as the older bi-pin instant start fixtures. The stationary socket actually has two contacts next to each other, the lamp pin bridges the contacts and completes the circuit to the ballast when both lamps are securely in place. The problem with these bi-pin instant start fixtures is that installing standard rapid start F40s will immediately blow the filament on one end destroying the lamp because the full ballast input current would be applied across it unless someone had shunted the socket. On the other hand, a F40T12/ IS lamp would cause a dead short across the heating winding of a rapid start ballast. It's these reasons modern instant start fixtures use single pin lamps, with a few exceptions, most notably the F32T8 lamp which typically is run on electronic instant start with shunted sockets or standard sockets with a jumper across the socket, although these lamps are sometimes run on rapid start or programmed start when frequent switching or dimming is required.
You are completely correct other than when you put a modern Preheat/rapid start lamp in the fixtures both cathodes actually survive. I even tried one shunted and one regular lamp to put the full ballast current on one cathode and it still survived, although glowing considerably brighter
@@BROKEN.WRENCH.GARAGE thank you for sharing your experience and knowledge about these old and obscure fixtures and lamps. I would have only guessed that the cathode wouldn't hold the ballast line voltage/current when inserted into a bi-pin instant start fixture. I enjoy learning new things from other lighting collectors on RU-vid. Since you mentioned the end was glowing considerably brighter, I wonder if that had the effect of slightly lowering the required starting voltage , acting like sort of a hybrid instant start/rapid start tube, if you will. I also wonder if using a modern rapid start F40 in a bi-pin instant start F40 fixture without shunting the sockets would result in an even shorter lamp life, than if all four sockets had been shunted so that no ballast input current could flow through the cathodes and make them glow brightly. I wonder when approximately the time period bi-pin instant start F40 fixtures fell out of fashion in favor of the somewhat more common F48T12 single pin lamps and sockets. Maybe like late 1950s???? I do know that the F40T12/CW/IS lamps were still available for replacement purposes until at least into the mid 1990s, they are listed in my 1993 GE lamp and ballast catalog, but none of my newer catalogs list them. My newest GE catalog is from 2016 and it has F48T12 lamps listed, essentially the modern day equivalent to the F40T12 /IS, since they both, along with the 60 inch F40T17 /IS are compatible with the same ballast. If you still have any F40T12 /IS lamps laying around and a slimline ballast for F48T12, I think it would be cool of you to do some demonstrations of them alongside a standard F40T12 lamp, in a future video. Your other many subscribers will probably appreciate it as well .
@@BROKEN.WRENCH.GARAGE sure that would be awesome, since this upload was the first time ever seeing a F40 /IS in a photo or video. I have however, seen a couple of different F48T12 slimline lamps in other youtube videos, and one lighting collector had a pair of ultra rare F24T12 slimline lamps operating in a strip light, magnetic ballast from about 2009, some of the very last magnetic fluorescent ballasts manufacturered before being banned due to federal minimum evergy efficiency standards (thank you, Government for taking one more freedom of choice away from me in the name of "saving me $$$ on my electric bill and protecting the climate " 😂🤬) and he had to remove the bi-pin sockets and install single pin sockets because he couldn't find any purpose built F24T12 fixtures. I've also seen a F40T17/CW/IS lamp on an upload from about 10 years ago, running off a F32T8 electronic instant start ballast wired for 2x overdrive. If you decide to upload a video of a F40 /IS lamp in the future, I along with your other subscribers would probably like to see a standard F40 operating next to it with the end glowing brighter as a demonstration on how an F40/IS lamp is really just a rapid start F40 with shunted end caps making them electrically equivalent to a slimline F48 and hence the slightly shorter rated life than a slimline F48 as listed in my 1993 GE catalog, because all slimline lamps have more robust cathodes to tolerate the higher striking voltage better than rapid start /preheat)
