The TEC-1B is an incremental upgrade to the TEC-1A.
The SHIFT key is now standard. The 8212 latches are replaced with 74LS273 IC’s, easier to buy.
The EPROM socket now accepts a 2732, double the TEC-1B 2716. With a switch either the lower or upper part ar switched into Z80 memory space. This allows the old MON1B and newer MON2 ROM to be used, so compatibility with older programs is achieved.

Publsihed in Talking Electronics issues 13 and 14. PDF of the articles here.