Question for IBM Selectric enthusiasts about keys

User avatar
snuci
Vintage computer guy

20 Nov 2018, 13:08

What, if any, models of IBM Selectrics came with Cherry key switches?

User avatar
snuci
Vintage computer guy

20 Nov 2018, 14:05

Okay, here's the story.

A company called CPT Corporation produced a CPT model 4200 that was a very early word processor. This system included a cassette based storage "console" that recorded keystrokes from a connected, modified IBM Selectric typewriter. Once you recorded a letter, you could play it back and the typewriter would type it out. I am still a little unsure how it works exactly but I have to dig into that a little more.

As noted in the CPT 4200 Training manual:
In appearance, the typewriter keyboard differs little from the standard office Selectric — only six keys have been added. However, hundreds of parts within the typewriter have been replaced to transform the Selectric from a mechanical to an electronic keyboard
I am guessing the keys and all internal mechanical parts have been replaced with a Cherry keyboard; essentially making the IBM Selectric a keyboard for input and a printer for typing out letters. I have a few cassettes that have letters stored. Anyway, I was just curious if there was an actual IBM Selectric model that had a Cherry keyboard or if this had been extensively modified to remove the entire mechanical keyboard mechanism. Here's what it looks like. Naturally, more pictures to follow when I can take it apart. The keys on the console are pretty cool too. This is from 1972 or so.
CPT 4200
CPT 4200
CPT 4200.jpg (225.33 KiB) Viewed 726 times

User avatar
Techno Trousers
100,000,000 actuations

20 Nov 2018, 15:11

After watching Chyros' video on the crazy complex analog internals of the Selectric symbol selection mechanism, I can't even imagine trying to do something like this.

Are you saying that all the pushrods, etc. have been removed and replaced with something else? This should be a really interesting tear down.

And can the typewriter still be used standalone?

User avatar
snuci
Vintage computer guy

20 Nov 2018, 15:20

Techno Trousers wrote: Are you saying that all the pushrods, etc. have been removed and replaced with something else? This should be a really interesting tear down. And can the typewriter still be used standalone?
I just got it last night and was confused about the Cherry keyboard. I will take pics to illustrate what this looks like but they are definitely Cherry M61 key switches in it.

codemonkeymike

20 Nov 2018, 21:47

They wouldn't need to remove the internals, the selectrics where designed to be able to have the keystrokes digitally encoded for things like teletypes and magnicard machines. You only need something like 12 sensors on the bottom of the selectric mechanism to turn every keystroke into a set of 1's and 0's. If they removed the selectric mechenism and replaced it with cherry components that would be odd, but they could use about 12 actuators to run the selectric mechenism and have it still function as a printer (like if you could cut of an inch or so of the selectic stems that are attached to the keyswitch and put the cherry mech pcb there).

User avatar
snuci
Vintage computer guy

20 Nov 2018, 22:41

codemonkeymike wrote: They wouldn't need to remove the internals.
I don't know exactly what was in them to begin with (I'll look around) but here are some quick pics while I have a little daylight light. How did they do in terms of what you were thinking?
Key Caps/ Cherry Switches
Key Caps/ Cherry Switches
IMG_4272.JPG (638.6 KiB) Viewed 638 times
Front view with keyboard folded out
Front view with keyboard folded out
IMG_4273.JPG (618.19 KiB) Viewed 638 times
Side view with keyboard folded out
Side view with keyboard folded out
IMG_4274.JPG (523.65 KiB) Viewed 638 times

User avatar
snuci
Vintage computer guy

20 Nov 2018, 22:48

Screw LEDs. Incandescent bulbs is the way to go! These are the key switches on the console portion. They light up.
CPT key switches with incandescent bulbs in the centre
CPT key switches with incandescent bulbs in the centre
IMG_4276.JPG (635.66 KiB) Viewed 633 times
CPT switches with hollow opaque key cap
CPT switches with hollow opaque key cap
IMG_4278.JPG (662.85 KiB) Viewed 633 times

Layer_Shift

25 Nov 2018, 21:27

I made something like this for a beamspring. I am actually finalizing the design as I find time but check this out.

The first link has a short video to show its actuation.

https://www.instagram.com/p/Bpvq7QpF1gf ... 6b0hlvz0k8

https://www.instagram.com/p/Bpp38IZl94B ... sk7hatxa01

Is this what you are looking for? If so I am hoping to set up another test run in the next week and validate tolerances. The ones in the above links had a few slight issues that I am working out now.

Sent from my PH-1 using Tapatalk

Post Reply

Return to “Keyboards”