[GreenKeys] TWX ASR33 and Bell 101 modem - answers to my previous questions

[Jeff G]

So I emailed the list a week or so ago that I got a TWX ASR 33, and I asked
some questions. While this info is all anecdotal technically, I did a bunch
of research and found the answers:

I asked if a Bell 101c dataset could technically talk to a (slightly more
modern) modem and communicate. Answer: Yes, although it may have to be an
older modem. I found this cool vid here that actually shows a Model 28
using a Bell 101 dataset to connect to another modem:
https://www.youtube.com/watch?v=yco4w3_DaMI

I'm really hoping I can get mine to do the same! There's a lot of
explanation in the vid, so fast forward about half way if you want to see
the hands-on stuff, but really for the most part he does a great job
explaining everything. I might have to see if he has any resto videos of
getting the dataset going.

Forgive me if this is already common knowledge to most, but for those
wondering about what it takes to convert a TWX 33 into a "computer" 33 -
the answer is: Not much! After poking and prodding I found mine has the
UCC-3 call control, and a manual tape reader (on/off only). While many feel
that you need to replace the TWX guts with a UCC-6, you don't really have
to, at least using this one as an example. The SMD boards between a UCC-6
and my UCC-3 are only different by a couple resistors really. The UCC-6 SMD
board allows for either 0.020 amp or 0.060 amp use, whereas the UCC-3 board
is initially set up for the dataset, but really just swapping out 2
resistors, and you're now identical to what's in a UCC-6 SMD board, and the
schematics give you the proper values of resistors to use for either
current range.

I found this document which really has all the right info all in one place
here, especially the schematics and resistor values for the SMD boards:
http://vtda.org/docs/computing/Teletype/WDP0033_WiringDiagramMode33PrivateLineSets.pdf

Also the UCC-3, at first glance, is missing the tape reader power pack. I
found it's just relocated in the base above the Bell dataset due to the
dial.

So I'm hoping that once I sort out the 58 miles of wiring, I can just wire
in a switch or two, or maybe a couple relays to switch between the dataset,
and a standard 20ma computer loop. There are a LOT of wires between the
dataset and TTY, but most of them are for all the buttons and lights on the
call control it seems. I'm still doing a little reading and schematic
viewing; been something fun on a rainy day while I wait for some parts and
things to come in. I'm also a little more confident in finally fixing the
gummed up keyboard on my 32, and maybe trying to get the HAL ST-6 to
actually talk RTTY on the actual radio (ITTY works great!).

(I won't mention the 43 or the 19 yet *smirk*)

Jeff KC3GJX
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