cant say I have seen such tubes made by tungsram before! very interesting find I THINK the electrical specs of these are about the same as a 10-13W PL-C lamp or 13W T5, so im surprised they ran as a pair in series!, (although It reminds me of how I managed to get a pair of 10W 2Ds running in series!) the shorter Asian spec 13 inch 10W T8, runs at 0.23A 55V or so, and a pair of those would run nicely in series off a 20W Choke I imagine

That's an interesting find Tom. I don't recall seeing this wattage in such a length, quite a low power density!

I’ve got some modern osrams in colour 827 in this length. Seem common in the continent.

These are interesting tubes indeed. They give a nice colour, halfway between the continental 25 and our original UK Natural, a nice soft cool white colour. I can imagine the Osram 827 version have a nice brightness Pete, get them paired up on a 20w choke! @ Dez I'm surprised you managed
to work a series pair of 10w 2Ds! There appears to be no indication of country or date on these but I suspect they're possibly from Hungary c1970s.