Nixie Тube Calculator Restoration! — Искра-121

Join us in restoring this beautiful Soviet-made 1977 Iskra-121 calculator (Искра 121) with a Nixie tube display!

Download the technical manual for the Iskra 121 (in Russian):

Download schematics for the Искра 111и power supply (very similar to the Iskra 121 PSU):

Support us on Patreon with a $2 contribution!

Featured tools:

Production tools:

Music:
Creative Commons — Attribution 3.0 Unported— CC BY 3.0

Thanks for watching!

#workshopnation #calculatorrestoration
#nixie

[Zardox-The-Heretic-Slayer]

I imagine that you're getting a big enough voltage drop due to the bulb limiters/meter current shunt to stop the supply working properly, try measuring the voltage on the mains side when you turn the powersupply on and see if it drops.
also; it's worth noting that using NOS transistors etc isn't always a good idea due to the tin whisker phenomena that plagues these devices so it's best to try and find equivalent new transistors.
positive ground was very common back in that era, I still have flashbacks to when I was a kid, taking the back off a TV and getting a giant shock from the metal chassis.

great video

[tonyhussey]

Incredible how electronics have changed only in the past 50 years... Fascinating. Those Nixie tubes have a beautiful glow

[martinest]

Absolutely amazing ! Great video, great editing and production. Beautiful content

[skeeveskeeve]

Thanks for making these outstanding videos - this channel is under-appreciated.

[h.cavidarabac]

Those pink cables and circuit boards looks delicious!

[freezetile]

The rotary switch on the front is most likely a decimal point selector, often seen on 70's desktop calculators from the Eastern and Western Bloc.
"B" would be the floating point mode, while the other settings would fix the decimal point at that position on the screen (e.g. the "5" setting would leave 5 digits after the decimal point).

[MegaSuperCritic]

There is certainly a beauty to these devices. Such a fascinating period of technology, the aesthetic of the time and environment is so identifiable. Awesome channel!

[dennistucker]

This calculator looks a lot like the first electronic calculator I ever saw. I was amazed by the sight of it in operation.

[JamesPearson]

Thoroughly enjoyed your video, thank you. I really appreciate the time you take to walk us through your troubleshooting along with your honesty and curiosity. I build my own analogue synthesizer modules and I learned how to create a dual power supply. When I saw you puzzled about the +ve leg of the capacitor on the ground I wished I could tell you that it was a because you'd found the actual ground between the +ve and -ve supplies. Most likely it's a full wave rectifier and the transformer secondary will have a centre tap, which becomes the relative ground.

I'm inspired by your efforts and perseverance with this project and hope you manage to revisit it to complete the repair. For sure there's bound to be plenty of complex work ahead, but I hope not too much!

[valiant]

Loving the channel and the videos you're putting out! The Soviet electronics might be a bit crude but thats what makes them fascinating & beautiful!

[janesmith]

These videos are so incredibly satisfying to watch

[alexserdukov]

Your shopping trip for transistors looks very similar to the Shurick's one from "Ivan Vasylsyevich" movie 😀

[VintageProjectDE]

That's a great piece of history!
I like how you show the process and don't skip the ups and downs. And that market is awesome! :)

A few observations from my own learning curve:
Positive ground and negative voltages aren't uncommon in old devices. It rather appears they were the standard into the 1980s.

If you encounter metal can transistors like the TO-3 package you showed it is safe to assume that none of the contacts should be grounded (to chassis). The insulating layer you showed most likely is some form of mica and ensures that the case, probably the collector, doesn't touch the metal of the case while allowing for heat transfer. Depending on the current it has to carry it may be required to add heat transfer paste between the layers without shorting the contacts.

Voltages: Whenever tubes are involved voltages are going to be high. I think I've seen +110V and -110V here. They can even go beyond that in other devices.
Protection against accidental contact hasn't been a thing back then. It was just assumed that service people were aware of it and prepared accordingly. Thus anything metal may have voltage on it.
And that's also why I decided to get myself an isolation transformer. Probably saved me from a surprise a couple times.

Mains input: This one has a decent transformer on the input side that separates the rest of the circuit from mains. It is a good idea to also check winding resistance before powering up an unknown device.
If the meter shows open circuit ("O.L."): The winding may be broken or disconnected.
If it shows below, say 100 Ohms: There may be a short in the winding. YMMV, though. The resistance depends on design, expected currents, and core material used for the transforner. Over time you can gather experience for reasonable values.

[BiohackerHubUK]

Wow and you’re also Russian-Eng bilingual, dang. Proper genius

[ckovalev]

Great work, Thomas! Waiting for part II :)

[MrChanghma]

I'm a huge fan of this kind of stuff❤❤❤, you are a born genius.. God job... Doing awesome sir

[tze-ven]

I remember when I was in the college, I was baffled by the lab instruction manual in my electronics class. It always start with "1. Turn ON the power". I was thinking to my self, isn't it clear that we need to turn it on to be able to see the result? It wasn't till my mate troubleshot for hours looking for an answer as to why his reading was incorrect. When the tutor finally came to help, he immediately noticed that one part of circuits has its power in OFF position.

[TomKappeln]

Who could resist Nixietubes or VFD's ???
Outstanding videos !

[LetsPlayKeldeo]

Amazing work ! I hope to see more like this in the future !

[Ioccy]

This power supply uses a "hard start" oscillator which won't start if you gradually increase the voltage. Your dim bulbs are preventing it from starting oscillating.