Tuesday, September 03, 2019

digital clock



Some additional detail. A short photo essay to expand on the above FB post. [the FB link does not seem to be fully live. Try this instead]

The circuit working on my bench yesterday. Link to the video. It keeps time from the 60Hz line frequency so it is pretty accurate unless the power goes off in which case it needs to be reset. It doesn't know about daylight savings time. It does not dim at night. It's big and heavy. But still pretty cool to watch.

In the very early 70s, while a student at UofToronto, I found giant neon nixie tubes at a surplus shop in the electronics market then around Yonge and Wellesley.

I was told those tubes came from the stock market display board at the TSE (now the TSX). The display tubes for this vital board were changed regularly and these were the rejects. I think they were expensive, maybe $5 each?. I was a student so couldn't afford new ones then. In the 80s, I replaced those tubes with these real NEW ones that were still available then, about $30 each. Advertised on EBay now for US$200 each for USED ones.

Digital clocks were a very hot item then and there just weren't any BIG Digital Grandfather Clocks, so I decided to build one. Because of the used tubes, this is a reuse project!

The presentation needed to be impressive so I enlisted the help of a friend who was a better woodworker. He helped me with the cabinets made from mahogany (which you could buy then) and a huge sheet of 1/4 inch smoked plexiglass. Until yesterday this clock was almost six feet tall and very heavy and awkward. It was not very stable on a floor but it never fell over! It did not have levelers at the bottom so needed shims to be vertical on a old slanted floor.

I had moved this clock wherever I went for the past 45 years. I moved it maybe ten times. It was coming apart at the bottom and needed to be fixed.

The big space under the clock was intended to house an electronic pendulum which never got built. Nor the electronic chimes. So there was really not the need for the big space. Yesterday I shortened the cabinet and made some repairs and improvements. Now it fits on a desktop or shelf.

Built with six fancy Burroughs special 17 pin sockets, hand wired and supported with a piece of wood.

The bottom of the clock board.

Mains power supply. The nixie tubes need 180 volts. The rest of the circuit used low voltage. This made both. I cannot believe it worked for 45 years!

The board layout.

Then in 1976 Heathkit introduced a digital floor clock GC-1195 and digital shelf clock GC-1197. The first commercially available digital "grandfather" clock. Popular but not a huge success.

Their display used wedge based incandescent lamps that burned out frequently. Heathkit offered a Winchester chimes option. No pendulum.


I got busy with school and never made another clock.

Thanks for your interest

George Plhak
Lions Head, Ontario, Canada

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