The TR-5 and TR-750 were cheap amplifiers designed and launched in 1964. Although suitable for a range of purposes, they were marketed as an add-on to the Micro-6 and Slimline radios. By using a pair of them, they could be used as stereo amplifiers. One Sinclair ad stated:

MORE MICRO-6 DEVELOPMENTS

Because of the enormous interest in the Micro-6 we at Sinclair Radionics have been devoting much of our time to the development of accessories which add to its usefulness. The first of these, the TR750 Power Amplifier was introduced last month. This remarkably low-priced, high performance design has, of course, a great many applications but in conjunction with the Micro-6 or the Slimline it can form a really powerful car, home or portable radio.

Neither amplifier appears to have stayed in the Sinclair range for very long, only being advertised during 1964 and thereafter disappearing into oblivion.