Texas Instruments SR-56 LED Programmable Calculator, adapter cannot be found, but any charger/adapter, that is 115 volts and 60 hertz, should work.
NATIONAL MUSEUM OF AMERICAN HISTORY (SMITHSONIAN) - their description in of the one in the museum follows below:
Texas Instruments SR-56 Handheld Electronic Calculator
Description:This scientific calculator is a modification of the Texas Instruments SR-50A and a less expensive device than the contemporary SR-52. A handheld electronic calculator, it has a black plastic case with an array of forty small rectangular plastic keys. In addition to ten digit keys, a decimal point key, a change sign key, a total key, four arithmetic function keys, a clear entry key, and clear key, the calculator has twenty-one further keys. Many keys (including some of the number keys) take on a second function if the "2nd" key is pushed. This second function is indicated on the keyboard above the key. Texas Instruments advertised this as a programmable calculator.Text above the keys reads: TEXAS INSTRUMENTS SR-56. Behind the keyboard is a switch that may be set at R (radians) or D (degrees). Next to it is an on/off switch. Behind the keyboard is an LED display that shows ten-digit positive and negative numbers and two-digit positive and negative exponents.The calculator has a jack for a recharger/adapter along the back edge. A sticker on the back gives instructions. It reads in part: TEXAS INSTRUMENTS (/) SR-56. It also gives the serial number SR-56 2400279. It also reads: Assembled in USA. Above the sticker is a battery compartment. A mark below the sticker reads: LTA1677.Unscrewing three screws on the back reveals the workings of the calculator. It has six chips, three relatively large. One of the large ones is marked: TMC0538NL (/) P 7650. This is a TMC0538 chip, manufactured in 1976. Another is marked: TMC0501NL (/) EP 7706. This is a TMC0501 chip, manufactured in 1977. The third is marked: TMC0537NL (/) AP 7644.The calculator comes in a black plastic, cloth-lined, zippered case with loop.
