Many years ago, I bought a lot of miscellaneous logic ICs at a flea market or hamfest. These ICs were RCA HC/HCT devices, many marked as engineering samples, and some marked with either an RCA internal number or a house number. Some of them had little sticky labels on top. I've never been able to find a cross-reference for them, so today I typed up the numbers I've got: https://github.com/chapmajs/rca_cross_reference This is a typical sheet of the ICs: http://i.imgur.com/Fk59VNL.jpg Funny to see regular 74HC/HCT series logic in white ceramic packages! If anyone has more information, or a full cross-reference, please let me know. You can send a pull request on GitHub, or just email me off-list and I'll add them if you're not a GitHub user. There is probably some pattern to the numbering system. In typing this up, I noticed that the starting prefix (TA or P) doesn't seem to have any meaning w.r.t. the device function. The first two numbers of the code are 11 for HC or 13 for HCT. Thanks, Jonathan