Hi, recently I accidentally bought two 970 mm 40W T12 tubes (thinking they were the ~1200 mm tubes) and I don't have a ballast for them. Now that I have them I want to find a way to run these, but every time I try to search for a ballast all the results are for ~1200 mm tubes. According to the comments in here:
https://www.lighting-gallery.net/gallery/displayimage.php?album=1601&pos=171&pid=223955 ,
these tubes run at 0.56A and supposedly work on 35W metal halide ballasts, however the choke variant of these doesn't seem to be available here. I really want these tubes to run on magnetic gear, but if electronic is the only option, I prefer a programmed/warm/slow start. How can I find either the correct ballast, or one that approximately matches the tube specs?

Isn't the 0.56A also the rating of 1500mm (+/- something) 58W T8 lamps?
Edit: My memory failed me here, as RRK mentionned bellow, the 58W is rated 0.67A...

But if everythiing else fails, a 0.37A of "1x 18W T8" with about 0.166A "PL-S7..11W" ballasts in parallel shouldn't be that far off (they will both be a bit lower as the short 40W has a bit higher arc voltage, but not too far to create real problems, lower current is not as problematic as higher than rated current would be)...

No. 0.67A for 58/65W lamps.

For 230V world, probably a combo of single tube 18W choke and 7/9/11W choke in parallel will work with slight underdrive.

The F40T12/1m tubes indeed require a unique ballast.  It should have a voltage/current ratio of 335 Ohms when run on 220V 50Hz.  The reference spec of the tube itself is 556mA at 81V, with filament preheat current of 828mA.  The starter can be any standard type delivering a pulse of >400V and with a non-reclosure voltage >140V, so basically same ignition characteristics as the F30T8.

However, you should not be afraid to under-run these tubes.  This type was in fact intended for operation at either 40W or 25W (and the T8 equivalent was 36/23W).  For some reason manufacturers seemed not to dual mark these tubes and sold two separate ratings, even though it was technically (almost) the same tube - I suspect the only difference may have been that the 40W had cathode shields, whereas types marked 25W omitted those for a small cost saving.

This F40T12/1m when run at 25W uses another unique ballast with V/C ratio of 605 Ohms and short circuit current 450mA.  The tube then operates at 290mA 94V and 24.5W, same starter specs as above.

The ballasts for both of these ratings of 970mm tubes are still available - for instance the Vossloh LN 36l.342 is for 40W operation and the Vossloh LN 25.346 for 25W.  They can be bought at https://houben.eu/produkte/houben-lichttechnik/betriebsgeraete/fuer-leuchtstofflampen/elektromagnetische-vorschaltgeraete/standard-vorschaltgeraete-14-65-w

However, since you are in Nederland maybe I can find you some for free.  I am pretty sure we have a small stock of these left in the ballast lab at Sylvania Tienen, certainly the 25W and maybe also the 40W.  I will have a look next week.  Most of our ballasts will be scrapped in the coming months as we move to a new location, so if you are able to call by you are welcome to take whatever you want!

The F40T12/1m tubes indeed require a unique ballast.  It should have a voltage/current ratio of 335 Ohms when run on 220V 50Hz.  The reference spec of the tube itself is 556mA at 81V, with filament preheat current of 828mA.  The starter can be any standard type delivering a pulse of >400V and with a non-reclosure voltage >140V, so basically same ignition characteristics as the F30T8.

However, you should not be afraid to under-run these tubes.  This type was in fact intended for operation at either 40W or 25W (and the T8 equivalent was 36/23W).  For some reason manufacturers seemed not to dual mark these tubes and sold two separate ratings, even though it was technically (almost) the same tube - I suspect the only difference may have been that the 40W had cathode shields, whereas types marked 25W omitted those for a small cost saving.

This F40T12/1m when run at 25W uses another unique ballast with V/C ratio of 605 Ohms and short circuit current 450mA.  The tube then operates at 290mA 94V and 24.5W, same starter specs as above.

The ballasts for both of these ratings of 970mm tubes are still available - for instance the Vossloh LN 36l.342 is for 40W operation and the Vossloh LN 25.346 for 25W.  They can be bought at https://houben.eu/produkte/houben-lichttechnik/betriebsgeraete/fuer-leuchtstofflampen/elektromagnetische-vorschaltgeraete/standard-vorschaltgeraete-14-65-w

However, since you are in Nederland maybe I can find you some for free.  I am pretty sure we have a small stock of these left in the ballast lab at Sylvania Tienen, certainly the 25W and maybe also the 40W.  I will have a look next week.  Most of our ballasts will be scrapped in the coming months as we move to a new location, so if you are able to call by you are welcome to take whatever you want!

very interesting James! I have often wondered what the exact ballast specifications for the 970mm 40W T12 was, so thank you for sharing that (a fair while back I was able to find a copy of the IEC specifications for fluorescent tubes from 2002, https://www.lisungroup.com/wp-content/uploads/2020/02/IEC60081-2002-Standard-Free-Download.pdf but it only lists the 970mm 25W T12 tube)

but I am wondering James, what is your source on the 40W 970mm tube also being dual rated for 25W? I have trawled through quite a few catalogs and I have not found any mention/reference of that, the 25W 970mm T12 and 40W 970mm T12 have such different current ratings, that I find it hard to belive it would be possible to produce a tube that would operate satisfactorily on both sets of control gear, especially for example  say if you had a tube built with heavy cathodes for 0.56A operation, I imagine it would never get the full preheating current from a 25W choke, and thus it would always strike cold and sputter leading to poor life

the only tube I know of somewhat like what you describe is the Thorn 85W and 125W dual rated tube, and even then from speaking a couple collectors who have used them in the past reported poor life from them (and keep in mind on that tube the 85W side of thing is rapid-start 3.6V, starterless control gear only so they would be able to use heavier cathodes knowing they are heated by a fixed voltage source rather then a current source)


so I am very interested in hearing more about this Dual rating of 970mm tubes as this is the first time I have heard about it

@James, unfortunately I'm not able to go to Tienen as I still have school and I'm still learning to drive so I don't have a car. Unless you are willing to ship me one, I unfortunately have to pass your offer. Thank you though!

@RRK, thank you, I will try this if James's option doesn't work out somehow.

@cassss590 I found 3pcs of the 25W 970mm ballasts, and can post these if you wish.

@LBF - the info about dual rating is only present in the Sylvania datasheets.  It seems the same lamp was made for both ratings but usually with cathode shields for 40W and without in case of 25W rating.  I was also surprised by this in view of the different cathode loading and preheating.  It's not impossible that it is a mistake in the specs.  The only way to be sure now would be to check the cathode characteristics of each.

@cassss590 I found 3pcs of the 25W 970mm ballasts, and can post these if you wish.

@LBF - the info about dual rating is only present in the Sylvania datasheets.  It seems the same lamp was made for both ratings but usually with cathode shields for 40W and without in case of 25W rating.  I was also surprised by this in view of the different cathode loading and preheating.  It's not impossible that it is a mistake in the specs.  The only way to be sure now would be to check the cathode characteristics of each.

very interesting James! thats espically interesting that it comes from Sylvania, how many different types of 970mm tube are listed exactly are different sorts for different cathode voltages listed also?

I ask because this is something else in itself, if you follow the link in the original post above, and read the description and comments underneath it, you will see that I do note that 40W 970mm tubes did come in both 9V and 3.6V cathode versions, and I have explicitly seen 3.6V 970mm 40W tubes from Sylvania, so I would find it even more implausible that a low resistance cathode 970mm 40W tube would be rated for 25W use also since it would barely get any preheating at all

unless when said 40W tube was explicitly rated for 25W operation it was said to be *rapid start* operation where constant cathode heating is present, but I am not sure if I have seen a 25W tube in Rapid start specification, all the ones I have seen have been preheat/switch-start/9V cathode tubes

that being said! I do note quickly checking a modern Sylvania Catalog exerpt, a 25W RS specification tube is listed

https://www.luckinslive.com/data/3115d63e-c903-494f-af76-b2ff034517be/c1e21c7b-6143-4a69-a9d2-b9164855c107.PDF

which is very curious in its own right as no such tube exists as an IEC standard anyhow, unless the "RS" is a Typo there? I note that the 65W/80W tubes also have "RS" next to to them which cant be true since thats inherently a quickstart tube

so again all quite interesting!

@James, sorry for the late reply, I was quite busy. Are you sure the 25W ballast won't somehow damage the tubes? If so I'd be happy if you can send me the ballast(s).

Seen 1m 36W T8 lamps running on 25W T12 ballasts and they are running well. 1m 40W T12 should do fine on 25W ballast.

Seen 1m 36W T8 lamps running on 25W T12 ballasts and they are running well. 1m 40W T12 should do fine on 25W ballast.

IIRC but do correct me if I am wrong, those are on the 220V 500Hz train lighting systems with the unique capacitor start, 0.35A ballasts that they have right?

so I would not use those as a reference for what might be alright or not alright, because those a unique system with their own unique ballast and starting method, so what might work alright with those might not work so well with a normal 50Hz glower-starter setup

I can agree with that, there is practical evidence as tubes don't live long on that setup.