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Comment by voxadam | Hacker News Reader

The Selectric is a fascinating machine. I highly recommend watching "IBM Selectric Typewriter & its digital to analogue converter"[0] by The Engineer Guy.

[0] https://www.youtube.com/watch?v=bRCNenhcvpw

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They are - I believe they’re electric rather than electronic, and theoretically can be powered by a hand crank. They also use a neat trick of a tube filled with ball bearings with a one ball gap so only one key can be pressed at a time (it fills the gap while pressed).

This made me curious. Apparently this part of the machine was called the "compensation tube". But it's much more elegant than you've said. When you press 2 keys in quick succession, the 2nd key press is "saved" temporarily by latching a spring, so that as soon as the 1st key is done, the 2nd key is struck.

It's essentially a 1 character buffer, which is apparently sufficient to give a very fluid typing feel.

https://www.youtube.com/watch?v=xuPduBVGf8g http://www.bitsavers.org/pdf/ibm/typewriter/selectric/CE_ins...

Thanks very much for the extra info.

That is correct. The Selectric (and Selectric II and III) are entirely electric. Later Selectric variations, like the Mag Card II, introduced electronics in a separate console or in a board fitting at the back of the machine, but the typewriter proper remained electromechanical, where the only electric part is the electric motor.

The compensation tube is a cool design.

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