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ASR-33

I am no longer active in this hobby for the foreseeable future. 
I will no longer maintain or update the website, but I will leave it accessible to the web for as long as possible (years).

 

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Imsai 8080
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ASR-33
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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!
 

DSCF1349a.jpg (405186 bytes)
My ASR-33
 

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 operation. 

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 print head. 

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.
 

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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 print head!

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!
 

2008-05-14 Teletype 006.jpg (1488317 bytes)
Pad turned to goo (photo center)

2008-05-14 Teletype 012.jpg (1617914 bytes)
Hammer goo on the fingers

2008-05-14 Teletype 005.jpg (1465332 bytes)
New printhead with rubber foot on hammer

 

Teletype Links

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/
 

 


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Copyright 2008 Bryan's Old Computers
Last modified:
October 16, 2009