The Numitron: An obvious idea that wasn't very bright

The numbers don't look good, Jim.

Links 'n' stuff:

Fran Blanche's video on Nimo tubes:
(there are plenty more videos to discover on her channel, too!)

Technology Connections on Mastodon:

Technology Connections on Bluesky:

Have you ever noticed that I've never done a brand deal? That's all thanks to people like you! Viewer support through Patreon keeps this channel independent and possible. If you'd like to join the amazing folks who fund my work, check out the link below. And thank you!

[TechnologyConnections]

SOME ADDITIONAL CONTEXT:
I goofed here by not making clear that these wouldn't be naked in an actual product. They'd be placed behind a transparent panel, usually tinted which would reduce the impact of some of their worst flaws (however, I've seen some contemporary products which used these tubes and they're... better but still not great). Really, my issue isn't with the concept - it lived on much longer than the Numitron! My issue is with RCA's version of it: though pioneering, it wasn't very polished.
(original pinned comment): Did you notice in some of the B-roll shots that they actually look more readable when they're slightly out-of-focus? That's the real downside of using segments thinner than a hair!

[wlpaul]

eBay sellers are going to be wondering why there's a run on Numitron tubes for the next 24 hours.

[TubeTimeUS]

Numitrons were designed to be used with a filter in front of them. this solves the issues you talked about. they were very popular in avionics displays because they can handle extreme temperatures and vibration, unlike the other technologies (including early LED displays, which were unreliable). typically they're driven at a constant current (rather than a constant voltage) and, while turned off, fed a small current which keeps the filament warm without illuminating it. this makes the filaments last a very long time.

The displays you remember from '80s gas pumps were Panaplex displays -- basically a flat 7-segment neon-filled display designed for multiplexing. they also show up in a lot of pinball machines from the era. they required high voltage, just like Nixie tubes. although they can't handle a ton of vibration, they work well in extreme temperatures (think North Dakota in the winter) unlike LCDs which simply freeze and stop working. modern gas pumps have heaters to keep their LCD displays warm.

[Obladgolated]

Numitron probably wasn't intended to be anything other than a placeholder in the display market, intended to "hold the fort" for RCA until LEDs matured enough to replace them. At the time, RCA was a leading electronics company, locked in head-to-head competition with a relatively small number of companies that were exploring the rapidly-evolving digital semiconductor market. In 1971, LEDs were very expensive (as you noted) and quite dim (which you didn't). RCA wanted to "stake a claim" to the coming 7-segment display market without waiting for higher-output LEDs to become available.

RCA was still one of the leading vacuum tube manufacturers in the world at that time. The Numitron was a way for them to leverage their existing captive vacuum tube production capacity to get into the large-format 7-segment market early at fairly low cost.

It was a case of "good enough" holding the fort until "much better" became available.

[edamael]

I like how you spent the entire video trying to convince us how bad the Numitron was, but only managed to make us fall in love with it

[SeanBZA]

Numitron backing is grey because RCA used what they had in spades, the sheet steel with aluminium coat that was used to make anodes and internal structures for thermionic tubes, and this was proven to survive the glass sealing and gettering operations. Thus they used the standard tools they had in the tube plant, the flat anode sheet, slightly formed to be a stiff backing, and punched out the holes needed to hold the filaments. Then used the technology they had to make glass beads with wire in them, and sealed those into the holes, making the filament supports, and then simply used a flat section of that steel wire that was bent over to hold a length of thoriated filament wire, also a common item in the tube shop. Length and diameter calculated for the brightness needed at the applied voltage, and then simply placed in location, the ends folded over, then spot welded together to trap the tungsten wire under slight tension. Then at the rear spot welds to a lead frame attached to a standard off the shelf 9 pin glass base, and you have the complete unit. Glass top attached, and then evacuated with the standard roughing pump, and as a bonus because of the low voltage, and no need to maintain an ultra low vacuum, the roughing pump and the heat sealing of the tube is all that is needed to operate, no need for a getter to be installed, and no need to flash it, just a RF heating during sealing to get a high vacuum, then seal.

Incidentally there were small versions made, the same size as your common 7 segment LED displays, and they were very popular, as they ran off 5V, and interfaced with logic. They worked best using CD4049/50 CMOS level shifting buffers, as those would source or sink 50mA no problem. Using a buffer/inverter per lamp, and a BCD decoder or counter per digit allowed those displays to be bright, and as bonus you could also use the blanking input on the drivers to use PWM to dim them.

Project to replace those displays with LED ones worked, just that it really did not drop display current use, it was still 5A of current at 5V, though it was good in that at least you had a display that now was available, using a tiny HP 7 segment red display. Do one conversion and you had 16 numitron displays to use to fix others, so we only converted 3 boards to the LED version. Biggest problem was the resistor value selected was too low, so the LED displays were running way too bright, so had to be dimmed. Rather than destroying the cordwood board made to fit them, I simply used 2 6A silicon diodes in the common line, to drop the voltage seen by the LED displays down from 5V to 3V8, which made them dim to exactly match the old displays. Those 2 diodes were hard to fit in the limited space left on the display board. Users liked the new crisp displays, the bright version got complaints that it was so bright it was unreadable at night with dark adapted sight, and it lit up the entire cockpit. Display dimming had to match the other display, and that board used unijunction transistors, and had a disconcerting habit of the power transistor unsoldering itself from the wire leads, it ran so hot. Base lead unsolders itself, transistor is still conducting, runs hotter and lamp blows. Select spare lamp and it also blows, unless enough time for transistor to cool below 200C junction temperature. Would have been nice to have had some of the more modern mosfets that can handle 50A, but not at the age of that design.

[jeromewhelan]

My wife and I were electronic engineers, and as a learning project we constructed a TTL 24 hour clock with this display design. We thought it was sharp, and a friend fell asleep on our bed one night watching the clock display, he claimed he was watching it!

[Perfectly_Adequate]

“Ignore all the continuity errors. It’s a running clock”

Yeah not to mention the Krakatoa’s worth of lava lamps behind you

[mikeselectricstuff]

Displays like this predated microprocessors by several years - they were typically driven by discrete logic or even mechanical switches. By the time microprocessors were a significant thing, LED displays were available.

[joeschmo]

Numitrons, Nixies, etc., are wonderfully steampunk. You could be totally gangstah with a clock like that.

[Denamic]

"Now, I'm about to be rather unkind to this piece of alleged technology, " he said after basically calling it a piece of shit

[ephemeralstardom]

this is the sassiest, most impassioned video essay regarding the subject of mediocre electric numerical displays I have ever seen. I could listen to you talk all day every day!

[WillMoff]

"Numitron, take out Bumble Bee while I fight Prime" ~ Megatron 1972

[frugalprepper]

I know the guy who did the first 7 segment LEDs for RCA. He designed them and worked out the production of them. He worked there in the 70/80s. He has an extreme case of OCD. He is retired, and I have been to his apartment, and he has 10's of thousands of little electronic parts all organized on shelves in little bags with numbers on them, and he has the all inventoried in a database, so he can find them, and he still builds all kind of electronic projects. He lives in Springfield, Ohio. I met him on the Ham radio repeater.

[Fanzindel]

The more he poops on those poor little Numitrons, the more I love them 🥹

[humanetiger]

Numitron to me looks pretty dope. Elegant thin numbers, the amber glow, the smooth transitions between on and off state of each line. Everything - almost perfect design.

[naotak]

There's something beautiful about how old technology worked. The combination of the limitations of the available electronics and engineering of the time resulted in some unbelievably wild ideas making it into every day products.

[Mark_LaCroix]

I'm almost certain that the gray color for the backing was selected deliberately so that it *would* reflect a certain amount of light coming from the filaments, "blurring" the extremely narrow segment lines thus allowing the numbers to be more legible. You can even see the effect working in the medium shots of this video. Put a tinted filter plate in front of the display (like the kind used by other 7-segment displays) and it would block outside light from reflecting off the backing, further controlling the overall effect.

[brooksrownd]

About 20 years ago I sold a few NOS Numitrons via eBay to a guy in Germany who made clocks with them. I was a bit shocked that he paid to have them shipped international even though I couldn't guarantee they worked.

[TIMMEH]

I just loved the massive displays in Airports in the 70s and 80s which had flip over flaps for letters and numbers, and took bloody ages to roll over an entire line when it changed and made a racket doing it. The electronics that drove them must have been amazing. Dot matrix designs replaced them, now small screens all over the place does their job.