Teletype Repairs – Our ASR 33

A new motor capacitor is improvised for service in this 1965 Teletype model ASR 33

They’re slow, They’re noisy!

Teletypes were used as the interface console for a most 1960’s minicomputers such as the DEC PDP 8 and Honeywell DDP-316 . They were also used in television news rooms, post offices, libraries, and schools to deliver printed news or to connect to a computer remotely through a phone line. In fact, they operated like a telephone in that both sent data via a “current loop” connection.

Although people still used telephones during the 1970’s, as the decade wore on “glass teletypes” (CRT terminals) began to replace the Teletype for minicomputer and mainframe computer use. Was that it for the Teletype? Terminals were a more flexible, read data faster and were a quieter computer console. But the Teletype, especially the model ASR 33, was not dead yet. Many of the Teletypes that made it into the surplus market found a new life and use with microcomputer hobbyists. In the mid 1970’s the Teletype was still the least-expensive alternative. Speed was less of a factor.

As often described in magazines like Kilobaud and Byte the teletypewriter was slow and noisy, but it was also easy to use. Early micro manufacturers (MITS Altair, IMSAI 8080, etc.) built their computers with teletypes in mind as evidenced by the fact that they had I/O port circuitry that could by default interact with the Teletype’s 20 milliamp current loop. Further, manufacturers had not yet started making printers and displays for the home use budget.

The Teletype was actually 4 devices in one – a keyboard for console input, a printer for console display, a line printer, and a tape reader for input and papertape punch for output. This is what made these so useful – they also served as an I/O station and printer. It was the perfect all-in-one device for early micro users. IBM Punchcards very popular for minicomputers but not micros, cassettes were not yet prevalent and disk drives and hard drives too expensive.

Learn More about Teletypes

The Teletype Model ASR 33. This is our “bench Teletype”, the one we use for demos and testing computers that use a Teletype for I/O.

This Teletype is going to be paired with our Digital PDP 11/05 computer, come visit for a demo. The ASR 33 is still considered an important component in the support of vintage computing.