Here's what Numitron tubes in an actual product look like

I did put it back together

I like the implication that the concept of 'off' has a patent pending.

18:51 Soldering iron melted the jacket on the large filter capacitor while the green wires was soldered onto the post.

I like how the "actual product" is only marginally more professional looking (even on the outside) than your quick hackjob

Honestly they still look largely fine to me, even when displaying 88. The misplaced decimal point is a bit janky but nothing too unbearable by the usual standards of multi-segment displays. I’d guess that one thing which particularly helped to kill these was their power consumption. In Bob Johnstone’s We Were Burning he mentions one reason why the Japanese carmakers were desperate for new illuminated-display technologies: the single incandescent bulb in their car radios was consuming more power than the entire rest of the radio system combined, and it had a much worse lifespan to boot. A display with multiple incandescent filaments for each single digit can’t have been too attractive to anyone building something which might need to run off a battery. See also the Apollo program messing around with promethium paint.

That glare seems like it would be really annoying in a well lit darkroom

4:30 Fortunately, if it’s going to be in a dark room, room light glare is less of a problem.

Board would have been laid out using black crepe tapes of various widths, which made it easy to make curved tracks by pressing down with a finger, guiding it where you want. Pads would have been stick-on symbols or possibly rub-down transfers ( Letraset) Done at either x1 to make direct artwork, or at 2x size and photographically reduced. Double sided boards were done using red and blue translucent tapes, and seperated photographically. For simple low-detail boards like this, freehand drawing with ink pens on drafting film was also sometimes used.

at about 16:00 i'm hearing bigclive, "i will be back with the schematic, one moment please..."

That burn on the big capacitor looks for all the world like someone slipped with the soldering iron at some point and caught it.

As an old radio nut, I once saw an ad that read, "don't be vague, buy Sprague!" Hope this helps.

Since this is a darkroom timer, and you like connections, when we stopped using track tapes and started using CAD for PCB design the resulting files (Gerber) would drive a photoplotter: essentially an enlarger/reducer where the head could translate in x and y. The files would select an aperture (like a trace width or component pad) from a wheel of shapes and either flash the bulb (for a pad/symbol) or draw with the bulb on (for traces) to expose the film. We had a darkroom these machines lived in and the usual monochrome chemicals. The resulting plots would then get couriered to the PCB manufacturing place where they'd be used as masks for the photoresist on the copper-clad boards or make silk screens for lettering and other layers. These days we still use Gerber files, but they get rasterised for plotting in something more like a laser printer. In defence of Numitrons, at the time these things were more "futuristic" than the alternatives, and despite the failings were "cool". You do quickly get used to their quirks and the decimal point when reading them.

RCA made another Numitron called the DTF104B which solves some of the problems these tubes exhibit. They are top viewing so reflections are much less of an issue. I don't think they made many of them, though. Probably never made it past pre-production. Edit: I put a short video of one on my channel for those who are interested in seeing it.

Ah, the Numitron: the very best of 1930s tech made 40 years late.

According to Wikipedia, the 7492 is a divide-by-12 counter. It actually has separate /2 and /6 sections, and the /6 makes perfect sense for turning the 60Hz line voltage into 10Hz. The 7490 is a /10 counter to give seconds.

I like how legible the digits are at 9:48 when the camera is out of focus. They almost look like regular 7-segment LEDs !

I'm still not sure why I watch 26min videos on things I don't really care about... But your content is so relaxing and easy to watch that I now know more about dishwashers and turn signals then I ever needed to know :P

Back in 1985 I put a new FM station on the air, complete with a studio automation system. The automation was an early microprocessor setup that used IIRC, ten Numitrons in the programming display. Each day, the commercials and other events were programmed in using this display terminal. Within weeks of taking delivery, the Numitron filaments began to burn out. That sucked, because the tubes were soldered in, and it was a bugger to get to the bottom side of the circuit board to unsolder them. What's more, soldering and unsoldering connections repeatedly on circuit boards is a destructive process. The operators learned to 'read past' the bad segments, but you can only do that for so long, before too many segments are blown. I looked into finding sockets for these tubes, but never found any. I also looked into replacing them with large 7-segment LEDs, which were beginning to become available, but that wasn't practical either, for various reasons, mostly economic. I moved on to another job, without ever resolving the issue. I often wonder what the next engineer did.

"This is a darkroom timer" Anybody else suddenly smell fixer? Just me?

I think you inadvertantly found the perfect application of numitron displays by accident. That green filter cover i will bet anything it was supplied with either 2 or 3 of them. Green for developing panchromatic materials, you can use a specific shade of green partway through developing if you need to inspect the development. They could have had red and amber covers red for orthochromatif film and amber will generally be fine for darkroom printing paper.