The Z-50 amplifier was added to the Project 60 range in June 1970. The Z-30 was rated at 30 watts, so Sinclair decided to advertise the Z-50 as rated at 50 watts. However, the device expired at between 37-40 watts, so their designer suggested 30 watts as a rating; the final compromise was 40 watts. Perhaps not surprisingly, the Z-50 was not a particularly reliable device.

The amplifier needed more power than the Z-30, so yet another power supply unit - the PZ8 - was introduced to the Project 60 range in order to meet the requirement.