[GreenKeys] Tally 424 paper-tape reader works!

[Jones, Douglas W]

Yesterday, some of my students and I got our PDP-8 to (sort of) work with our Tally 424 high-speed paper-tape reader.  The reader was bought second-hand by the U of Iowa in the mid 1960s.  The writeup is here:
-- https://homepage.divms.uiowa.edu/~jones/pdp8/UI-8/log.shtml#2026-07-21

And there's a little animated video here:
-- https://homepage.divms.uiowa.edu/~jones/pdp8/UI-8/2026/07/21-TallyRunning.gif

The thing runs at 60 characters per second, not rocket speed, but nice.

We do have one big bug:
-- the data is inverted, our fault.

And one nit to pick:
-- the feed direction is backward from what feels natural, Tally's fault.
It's a bidriectional reader, but it's missing its reverse feed solenoid.  We do have a spare reader to cannibalize for parts, so we'll probably put in the missing part and run it in reverse.  As it stands, the pre-printed marking on the tape that says TOP must be on the bottom when you read the tape.  Grumble.

For those who like complex mechanisms, this paper tape reader has one constant-speed motor and 3 differentials in it.  The slack-arms that control the torque on the feed and take-up reels each apply torque to their reels by braking an associated differential, and the tape advance (in either direction) is done another differential with two solenoid-controlled slip clutches.

             Doug Jones