Strongly resembling the layout of the TR-67, the TR-77 adds a seventh transistor while continuing to sport two diodes, one varistor, and big 3.5" speaker. Power is supplied by 3 C-cell batteries. Getting into trivia, this unit is from early production. Don't be fooled by the different numbering system Sony used for the serial numbers on this model.
Transistors: 2T76 x 2, 2T74, 2T66 x 2, 2T85 x 2 [varistor: 1T41]