Ed wrote: >On opening it up I found that the circuitry includes a 74LS73 dual >JK FF, and a 74LS140 - very obscure - apparently a dual 4-input gate >of some sort. AFAIK, the '140 was only supplied in the "S" series (74S140). It's a dual 4-input NAND 50 ohm line driver. Best regards, Charles