[GreenKeys] Reader-run relay installation

[Don Robert House]

Doug,

You appear to be doing a fantastic job.  Congratulations on your
careful and painstaking restoration.  The motors in the 33 under
normal conditions of intermittent use did not get hot even though
the word HOT was stenciled on them.

One puzzle I never did figure out after working on hundreds of
33ASRs was a metal clip that was installed on some of the
sprocket feed machines.  The purpose of the clip was to cover
all of the ventilation slots in the rear of the cover behind the motor.
This seemed to be counterproductive at best.

The only possibility I can come up with is that the 33 machine
would not handle forms with carbon paper and no more than
a second copy which was with what we called NCR paper...
you know "carbonless copies."  With heat the second copy
would turn dark and the text would not be readable so maybe
someone thought the fan was blowing too much heat on the
two-copy paper???!

I know for sure that the machines we installed, we always
removed that clip.

Keep up the great work you are doing and thank you so much
for sharing.

All my best,
Don
K9TTY
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On 2 May 2014, at 9:10 AM, Jones, Douglas W wrote:

I've completed the installation of a reader-run relay in the CCU
of the Model 33 we're rebuilding.  Photos of the completed job
and links to the documentation are here:

-- http://www.cs.uiowa.edu/~jones/pdp8/UI-8/log.shtml#2014-05-01

Given the incredibly poor quality of the photo in the preserved
copy of DEC's instructions for installing the relay, I hope
these photos help others, and also, I note that our cable routing
was at least reasonable.

I debated lacing my wires instead of using zip ties, but DEC
always used zip ties in their work.  I also debated running the
wires on the right side along or even laced to the original TTY
wiring harness, but the length of the salvaged wire from the
relay to plug 4 was too short for that, so I did my best to follow
(approximately) DEC's original wire path.

Yes, I know how to lace cable.  And in other recent rebuilding,
I had to use that skill.  The motor on the Tally 424 "high speed"
paper tape reader had bad wires (crumbled rubber insulation) so
I had to replace them.  This involved replacing the lacing on
the motor windings.  The photo here shows that job in progress,
the new lacing job started and the old one still not fully removed.

-- http://www.cs.uiowa.edu/~jones/pdp8/UI-8/log.shtml#2014-04-25

The lacing pattern on the motor windings is not just a double
spiral (that's what I thought it was on first inspection.  It's
more complex, and the complexity is all out of sight, and tricky
to recreate.  The rebuilt motor runs well, almost silently and
warm but not hot.

		Doug Jones
		jones at cs.uiowa.edu
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