I started electronics and computer school in the military in 1969. The first main frame I worked on had vacuum tubes in the power supply. We used to sit on it to keep warm.
Nice. The oldest functional computing devices I've been able to use was some antique HP mini from the early 70s and a PDP11/34A that did frame test. I think the build date on that was 1976.
There were other devices that dated back farther that were simple computing machines, but no general purpose units.
The modem we used between the CPU and the HF radio was the size of a household refrigerator. The operating program was loaded by perforated paper tape.
I had positioners that worked on paper tape, but mine was all record size 5MB single-platter hard drives. Fun times.
Fun Fact: What was left of Digital Equipment Corporation advertised (in the early 90s) that they could convert your PDP11 to a PC based solution. We had them out, said "Here's our (specialty modified) PDP, can you help us?" The offer vanished from the website and they no longer did that type of service. Not saying our frankenstein machine did that, but it's highly suspicious. It had a bad CPU card, so it wouldn't work anyway as it just stuck a PC adapter on the bus. When we transferred the machines to another location the engineering staff there tried another solution after being told "Hey, the CPU is bad, won't work." They found out, especially after I visited, got an earful about how engineer spent money on the system, and just stared at me when I said "Yeah, CPU2 is bad."
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