Re-installing a TouchTone keypad in an ASR-33

Ethan Dicks ethan.dicks at
Sat May 16 17:15:06 CDT 2009

Hi, All,

I know I've mentioned this long-outstanding project before, but just
this week, I've had a couple of nudges towards getting it done...
First, Will Donzelli stopped by on his Eastward Progress to deliver
some PDP-8 gear to me, and in the process of showing him around my
Farm, I pointed out this ASR-33 w/110 bps modem in the pedestal.
Second, I just found the box of telephone parts with two pre-IC-era
touchtone keypads, one of which I'm positive I removed from the TTY
years ago when I was tearing it apart (in ignorance) to attempt to
remove the modem, etc., and make it a viable console TTY for my
(first) PDP-8/L.

So... what I still lack is proper documentation to know how to install
the TouchTone pads.  I'm thinking it'll be much easier these days to
find a PDF than it ever would have to find real paper in the 1980s
when I bought the TTY at Dayton.

My question (for now) is... how I can tell which of these two keypads
is likely to be the right unit.  They are superficially identical, but
one has 7 wires, the other 11 as follows...

Both: Green, Red, Black, White, Blue/White, Black/Orange, Red/Green
One: Purple, Blue, Orange, White/Green

There is what appears to be a date-code on the bobbin transformers on
the 7-wire pad of 3-77 vs 12-80 on the 11-wire pad.  If that _is_ a
date code, I'd wager the 3-77 unit is from the ASR-33 simply because I
don't think I would have been able to pick up a 3-4-year-old ASR-33 at
Dayton for $35 or so, but I can believe that a 7-8-year-old unit could
have been that cheap.  OTOH, I can see how a data device might need a
more complicated keypad (there appear to be additional levels of
switches compared to the simpler one, thus it suggests where the extra
4 wires are going).

I'm thinking that I probably just loosened the screw terminals in the
ASR-33 and removed the keypad to either get it out of the way or
because I thought I might recycle it into something else.  Now, give
that I know there are differences other than the modem in the one TTY,
I'm probably unlikely to attempt to convert it to a 6-wire
console-capable TTY, and would like to restore the modem-equipped TTY
to its original functionality.

Does anyone on the list know of a good resource for 1970s-1980s
telephone techology that is available (i.e., not something that
Western Electric/Lucent is sitting on that's for internal use only)?
I have PDFs for the mechanical bits of an ASR-33; those have been
floating around for some time (and I have them on paper, too, that
came with my console-capable TTY).  I lack any
modem-equipped-model-specific docs.  Those would be most helpful, as I
could reinstall the TouchTone pad in a few minutes once I knew what
wires go where.

Thanks for any tips and pointers.


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