V C F
The Digital Group
The Amazing ASR-33
The Teletype Corporation of Skokie,
Illinois manufactured ASR-33 (and several variants) Teletypes beginning in
the early 1960's as a light duty machine. The ASR-33 was an
electromechanical device, heavy on mechanical. Other than the many
electrical contacts, the only electronic parts were in the power supply.
To see one operate under the hood is to see a ballet of whirling cams and
shifting levers that can only be described as awe inspiring. Keep your
fingers out of there!
|Nowadays, it isn't too
hard to find someone who has never seen one of these. That wasn't
true 30 years ago. These things were everywhere! If you watched the
evening news, you would see and hear them or a similar model
clanking away in the background as part of the AP Wire Service.
Western Union used them to send messages all over the world, sort of
pre-email, email. They were the terminal of choice for minicomputer
owners. They also gained huge favor amongst computer hobbyist since
at the time, they offered nearly the only practical way possible to
generate hardcopy output from a micro. Timeshare users also used the
ASR (Automatic Send and Receive) Teletypes to connect though a modem
to a mainframe computer. My first experience with one of these was
on a timeshare service at my high school in the mid '70s.
The ASR-33 operated at 110 baud, or ten characters per second,
and we were happy to get it! Options included built-in dialing with
an internal modem, and configurations for RS-232 and current loop
The ASR 33 also included a paper tape reader and punch. Very
useful for the '70s hobbyist as a means to store and retrieve
programs. Floppy disk storage was far beyond the budget of most
personal computer owners at the time, and hard disks were only a
distant dream. The paper tape media was a durable and reliable means
of small program storage, but a longer program like BASIC would take
about fifteen minutes to load. This got old very fast, and hobbyist
were soon looking for better ways to work. When video terminals,
cassette storage and dot matrix printers were developed, the long
life of the teletype machine was drawing to a close.
|My ASR 33
I picked up my 33 from a salvage company just hours before it was
to be destroyed for scrap. It was in fair condition overall, but
needed a new print head and had a few scratches in the plastic. I
used fine grit sandpaper and wet sanded to buff the
plastic and remove the nasty yellow tinge. It was also missing a few
springs and the front label plate upon which the word
"Teletype" is printed.
It took quite some time to track down the needed parts for
repairs. The most difficult
part to find was the print head. The rubber pad that is supposed to
protect the print head from the print hammer had turned to mush, and
had worn down the lower half of about a half dozen characters. (See
photos below.) The repair was quite simple, after finding the new
After replacing the print head, I replaced
the gooey pad with a small rubber cabinet foot found at Radio Shack.
All the old goop had to be completely cleaned from the hammer before
sticking on the new rubber foot, as I did not want it to fall off in action and ruin
the new print head. I used Goof-Off (Home Depot) and an old
toothbrush to do this, as it does not leave a greasy residue--very
important thing here.
At VCF 9.0
|As for finding a
new print head... Good luck. This can be very challenging. Search ebay,
surplus outlets, Greenkeys,
garage sales, etc. You may have to buy another Teletype just to get the
If you have, or if you find an ASR-33... THE FIRST THING TO DO IS CHECK
THE PRINT HEAD AND HAMMER!! Did I say that loud enough? Do not operate it
for even one keypress before doing this!! If you have already replaced you
print head, it is still a good idea to inspect it regularly--I learned
this the hard way.
When I took my Teletype to VCF 9.0 in 2006,
it had been in storage for a while, and I did not check the condition of
the rubber pad. It fell off at the show and ruined another print head.
Erik Klein of vintage-computer.com
fame, was gracious enough to offer me a new one from a busted up Teletype
he owned--he gave me the whole Teletype just so I could get the print
head! What a pal! Thanks again Erik!
Pad turned to goo (photo center)
Hammer goo on the fingers
New printhead with rubber foot on hammer
Service manuals can be found at: www.pdp8.net/pdp8cgi/query_docs/query.pl?Search=teletype&stype=Partial+Wo
Also at Bitsavers: http://www.bitsavers.org/pdf/teletype/
Most excellent History of The Teletype Corporation: http://www.kekatos.com/teletype/