Radio Shack EC-100 (Version 1)

Date of introduction:  September 1972 Display technology:  LED-modules
New price:  $129.95 Display size:  8
Size:  5.8" x 3.5" x 1.5"
 147 x 88 x 38 mm3
Weight:  6.7 ounces, 191 grams Serial No:  A 11346
Batteries:  4*AA Date of manufacture:  mth 09 year 1972
AC-Adapter:   Origin of manufacture:  USA
Precision:  8 Integrated circuits:  TMS0103, 2*SN75491, 2*SN75492
Memories:   Displays:  DIS40, DIS95
Program steps:   Courtesy of:  Ken H. Meine

This boxy calculator does at first glance not look like a Texas Instruments product. Nevertheless could we proof its origins, the printed circuit board (PCB) located in a Radio Shack EC-100 (Version 2) is 100% identical with the PCB of the Longines Symphonette Electronic Calculator. And the label on the back side of the Electronic Calculator states: Custom manufactured for Longines Symphonette by Texas Instruments, Dallas, Texas. 

With Monsanto introducing the first commercial LED (Light Emitting Diode) display in 1970 and Texas Instruments announcing on September 17, 1971 the "calculator-on-a-chip", Bowmar/Ali Inc. of Acton, Massachusetts, USA launched the famous Bowmar 901B "True-Pocket-Size" calculator based on the TMS0103 with a suggested retail price (SRP) of $240.00.

It took less than one year before Texas Instruments announced the TI-2500 Datamath calculator in April 1972 with a SRP of only $149.95, its delivery in June 1972 to first customers in the Neiman-Marcus and Sanger-Harris department stores in Dallas, TX and its formally introduction on September 21, 1972. The SRP of the TI-2500 was reduced to $119.95 by the date of its introduction

Texas Instruments did not only provide to calculator manufacturers complete "kits" consisting of the TMS0100 single-chip calculator circuit, SN75491 and SN75492 display drivers, TIL360 Multi-Digit calculator LED displays and Klixon keyboards, they offered contract design and manufacturing of complete calculators, too. The first three products manufactured for retailers were:

Longines Symphonette EC
Montgomery Ward P800
Radio Shack EC-100

Please notice [K] engraving on the upper left corner of the Klixon keyboard! Rather confusing, this is actually the [ON] switch and Texas Instruments glued later a small metal piece with an appropriate label on the keyboard. Don't miss the Radio Shack EC-100 (Version 2).

Fellow collector Cleo McCall reported his EC-100 with Serial Number A 5490 having the [+=] and [-=] keys inserted in the wrong orientation.

Known serial numbers: A 5490, A 11346, A 16983

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If you have additions to the above article please email:

Joerg Woerner, December 5, 2001. No reprints without written permission.