
IBM mainframe tube module part II: Powering up and using a 1950s key debouncer - robin_reala
http://www.righto.com/2018/01/ibm-mainframe-tube-module-part-ii.html
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kragen
My first computer was a Heathkit H89 that my dad assembled about 1980. It had
a keyboard microcontroller (I don't remember, maybe an 8048), but it also had
hardware debounce: the keyswitches snapped together a solid copper electrode,
on one side, and four copper "fingers" on the other. The idea (as he explained
to me) was that the fingers would bounce out-of-sync with one another
(although they looked pretty identical, maybe there was a subtle difference I
couldn't see) and there wouldn't be any time when all four of them were out of
contact at once.

~~~
dws
Several friends and I went in on a bulk buy of H19 kits. Every one of us
discovered that we'd missed soldering the connections for the space bar.

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kragen
...is that you, Dave? I had no idea you had H19s!

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ChuckMcM
And all of that to keep from bouncing switches, which we do in software now in
a keyboard controller.

It occurs to me that we have the 6502 -> monster 6502 -> 'tube' 6502? Then we
could have 705 -> transistor 705 -> FPGA version? Sort of like playing Mozart
in different styles.

But I really liked the giant programmer console for the machine. Not sure why
but that sort of design ethos calls to me some how.

~~~
Animats
The IBM 705 came in a bigger version, the IBM 709, and there was a
transistorized version, the IBM 7090. The IBM 7090/7094 powered much of the US
space program of the 1960s and 1970s, and some of those machines were used
into the 1980s.

Those big control panels were mostly for maintenance use. UNIVAC separated the
operator and maintenance panels on their transistorized machines, and in
normal operation, nobody was near the maintenance panel. IBM kept a lot of
lights, buttons, and knobs facing the operators well into the System/370 era.
By that time you could debug the OS inside a VM, so all those manual controls
were unused, but it took IBM a long time to get rid of them.

~~~
ChuckMcM
So true, because no doubt somewhere there was an engineer inside IBM that
liked the blinking lights :-). One summer when I was working for IBM in high
school I got to work at the 'operators console' for a System 370. Pretty much
everything you did happened on a light pen enabled 3270 terminal, except the
IMPL (initial microprogram load) button was still a real switch, and the 'load
meters' which were pretty neat analog meters that read out system load were
useful for tuning the batch queue that was filling in batch jobs when ever the
meters showed less than 50% utilization. When it got over 95% the operator was
supposed to pause one or more batch jobs. At the time, IBM felt there was no
way the computer could know which batch jobs were "important" and which could
be pushed off.

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DrScump
The most striking difference to me as an operator was that the Series 370
console was more than just the terminal/screen. You had switches and lights
right out of a sci-fi movie, right down to rotary dials to set the address of
the boot device.

With its successor, the 303x, the console was a glorified terminal. (My
favorite command there was _quiesce_ [0], where you could bring activity to an
orderly freeze without ruining programs in process. I half-expected to hear it
sing "Daisy, Daisy" in slowing decrescendo.)

[0]
[https://www.ibm.com/support/knowledgecenter/en/SSLTBW_2.3.0/...](https://www.ibm.com/support/knowledgecenter/en/SSLTBW_2.3.0/com.ibm.zos.v2r3.ieag100/quiesce.htm)

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DrScump
I've done some image searches (to no avail) hoping to find images showing the
distinctive built-in screen and keyboard.

The screen displayed characters using a "font" that I've never seen elsewhere,
more resembling characters a human would handprint than a modern fixed font. I
was hoping to find images of that. I did at least find a partial image[0] of a
S/370 console with the light arrays that triggered my sci-fi comparison above.

[0] [https://popesixteen.files.wordpress.com/2012/04/picture-
syst...](https://popesixteen.files.wordpress.com/2012/04/picture-
system-3701.png)

~~~
pdw
Is this it? It looks pretty nice.
[https://en.wikipedia.org/wiki/IBM_System/370_Model_168#/medi...](https://en.wikipedia.org/wiki/IBM_System/370_Model_168#/media/File:HypertextEditingSystemConsoleBrownUniv1969.jpg)

~~~
DrScump
No, in these S/370 models, the keyboard was built into the desk and the
monitor was embedded in the console/control panel.

That's from memory, which in my case has no parity bits and is vulnerable to a
variety of exploits.

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SAI_Peregrinus
It's interesting how supposedly identical tube models look rather different.
Part of that is the getter depositing metal onto the top of the tube, and part
of that is probably that some tubes with the same number could come in
slightly different packages: different plate colors/sizes, different glass
size, etc. So while it looks like the Trigger 1 and CF1/2 tubes have been
swapped around they're probably correct. It's a bit like having parts in both
TO-92 and TO-18 packages, for the same part.

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jacquesm
The metal deposition inside the tubes is to get rid of the last of the Oxygen.
A bunch of Barium powder and an igniter would be placed in a small cup like
construction inside the tube during manufacturing called a 'getter', firing
the getter would vaporize the Barium which would then attach to the remaining
Oxygen molecules and subsequently deposit on the inside of the glass, the
largest and coolest surface.

~~~
SAI_Peregrinus
Good note. I mentioned the getter but didn't explain it, I should probably
have done so.

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peter303
One of my first TVs had vacuum tubes. When it failed, you took he tubes out
and tested them at a drug store or radio shack for a failure. You could also
take it to a repair store or call a rech to come. Very few vacuum tube tvs
were easily portable.

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icantdrive55
I find Vacuum tubes beautiful on so many levels.

Whenever I repair a old device, I cringe when I put the cover back on. I
always say to myself, I'm going to encase the old radio, or vibrograph (watch
timing machine) in clear plastic, but I'm always just too lazy.

