[GreenKeys] Reader-run relay installation

Sat May 3 13:23:52 EDT 2014

I have seen the metal clip in some machines and not in others.  I remove it on any 33's I work on.  

I also remove the low paper mechanical arm that is on some 33's.  The internal micro switch is not wired to anything on computer models, only on TWX or Telex machines.  It makes installing the cover easier.  

Wayne
KB1FDW

-----Original Message-----
From: Don Robert House <62.5milliamps at gmail.com>
To: Jones, Douglas W <douglas-w-jones at uiowa.edu>
Cc: Green Keys <greenkeys at mailman.qth.net>
Sent: Fri, May 2, 2014 9:18 pm
Subject: Re: [GreenKeys] Reader-run relay installation

Doug,
You appear to be doing a fantastic job.  Congratulations on your
areful and painstaking restoration.  The motors in the 33 under
ormal conditions of intermittent use did not get hot even though
he word HOT was stenciled on them.
One puzzle I never did figure out after working on hundreds of
3ASRs was a metal clip that was installed on some of the
procket feed machines.  The purpose of the clip was to cover
ll of the ventilation slots in the rear of the cover behind the motor.
his seemed to be counterproductive at best.
The only possibility I can come up with is that the 33 machine
ould not handle forms with carbon paper and no more than
 second copy which was with what we called NCR paper...
ou know "carbonless copies."  With heat the second copy
ould turn dark and the text would not be readable so maybe
omeone thought the fan was blowing too much heat on the
wo-copy paper???!
I know for sure that the machines we installed, we always
emoved that clip.
Keep up the great work you are doing and thank you so much
or sharing.
All my best,
on
9TTY

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
f the Model 33 we're rebuilding.  Photos of the completed job
nd 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
opy of DEC's instructions for installing the relay, I hope
hese photos help others, and also, I note that our cable routing
as at least reasonable.
I debated lacing my wires instead of using zip ties, but DEC
lways used zip ties in their work.  I also debated running the
ires on the right side along or even laced to the original TTY
iring harness, but the length of the salvaged wire from the
elay 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,
 had to use that skill.  The motor on the Tally 424 "high speed"
aper tape reader had bad wires (crumbled rubber insulation) so
 had to replace them.  This involved replacing the lacing on
he motor windings.  The photo here shows that job in progress,
he 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
piral (that's what I thought it was on first inspection.  It's
ore complex, and the complexity is all out of sight, and tricky
o recreate.  The rebuilt motor runs well, almost silently and
arm but not hot.
		Doug Jones
	jones at cs.uiowa.edu
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______________________________________________________________
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ome: http://mailman.qth.net/mailman/listinfo/greenkeys
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