Not many computer peripherals came housed in finely-crafted solid wood boxes. This is an acoustically-coupled modem, a Livermore Data Systems Model A, dating from around 1970. I think the wood of this unit is teak, although it might be satin walnut, both were popular finish-grade woods at the time.

Modems for computer communication over wire-lines go back to the 1950s. The technology however, goes back to the 1930s or 40s for radio-teletype (RTTY) application and specialised equipment such as the WWII digital voice encoder SIGSALY. In the 1960s, the advent of timesharing systems, and especially their commercialisation, created a market for modems that could readily be operated over the PSTN (public switched telephone network), i.e. the common telephone land-line. Getting a modem directly connected to the telephone line was an expensive proposition in the period, leading to products such as this - the acoustically-coupled modem - which didn't require involvement from the telco and didn't violate your terms-of-agreement with them for an ordinary telephone line.

The LDS Model A is a 'pure' modem, all it does is convert the two digital levels of a bit-stream to two respective audio frequencies. There is no dialing or call-handling capability, no bufferring or built-in error correction. All dialing, call setup and hangup must be performed manually. The circuitry is entirely discrete transistor, no integrated circuits. 14 transistors are used, about equivalent to the complexity of a transistor radio of the time.

The data-side interface is EIA/RS-232, the telephone side is Bell-103 compatible. It would function for data rates up to 300 BPS. The Model A supports originate-mode only.

Component date codes in this unit are 6908 to 7008, so it could be expected to have been manufactured during 1970. The serial number is 0858. Another Model A, serial number 0491, has been reported with date codes in early 1969. Reasonable extrapolation would suggest production of the Model A may have begun in 1968.


The acoustic coupler where the telephone handset sits.

With a then-common telephone handset in place.

A notch in the cabinet for the handset cord allows the lid to close with the handset in place.

A 163-type connector for power and DB-25F for RS-232 on the side. The DB-25F is wired as DCE.

Internal arrangement.

The circuit boards. Top-left: demodulator. Top-right: modulator. Bottom: power supply.

  Unit Log
Livermore Data Systems Model A
2017 Nov