Electronics > Projects, Designs, and Technical Stuff

NEC LD8121 VFD Tube pinout

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sergey:
Ok, finally got it! (was rather busy month at work, but that's another story).

So, used multimeter to find filament which was rather easy (one connection i saw, other one i just bruteforced :) it's a pair of legs on separate sides of the tube with ~45 Ohms between them.

Applied 3.3v across them, and tube drew around 26mA on filament. I didn't actually see gloving of the filament, so perhaps it could be increased to 5v as per IV-27 datasheet, but 3.3v volts worked fine for my purposes at this point.

On the anodes i've applied 12v and this lighted the tube up (it was drawing about 9mA on the anodes).

The only issue so far was that 13th segment didn't light up evenly -- it was darker comparing to the rest of segments. Hence the question: is it because of not enough power on the filament/grids or it's about physics of rather oldie tube?

Attaching a photo of the lighted tube (for those who're interested). And also attaching pinout of the puppy. Sorry for the crudity of the scheme, didn't have time to build it for scale or paint it! :) (and i do hope i didn't screw up when was drawing scheme on the computer).

Halbelunge:
Hey Sergey,

you have news with the LD8121 or need more informations?
I have bought me one of these and have found some more informations for this tube.

with regards
Benjamin

artag:
This is a bit of an old thread, but I came across it looking for info on the same tube (probably from the same vendor, still with stock !)

You mention a dim 13th digit. I believe this is because you're using DC to drive the filament (you don't say, but you don't say AC either). This means that one end of the filament is 3.3V more positive than the other, resulting in lower acceleration voltage at that end of the tube.

The ideal way to run the filament is with AC, using a centre-tapped transformer so both ends are varying positive and negative with respect to the most negative grid or anode voltage. It's possible to get away with DC if you can choose the right bias, but AC is better.

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