After completing the Postgraduate Diploma course I went to work for Mullards (a subsidiary of Philips) at Millbrook in Southampton, where the development and production of semiconductor components were concentrated. Germanium bipolar transistors were manufactured for use in products such as portable radios. Compared with thermionic valve radios, transistor radios were small and lightweight, and they also had the nice feature that they produced sound as soon as they were switched on!

The manufacture of discrete silicon bipolar transistors had just started at Millbrook, and I investigated some of their possible applications. Because they could be operated with maximum internal temperatures of about 150°C, compared with only about 70°C for germanium transistors, they could operate at higher ambient temperatures and/or with higher power dissipations. To illustrate that, I made a medium wave radio using silicon transistors that operated in an enclosure at an ambient temperature of 100°C, and demonstrated it at the London Radio Show in 1959.

That radio was deliberately made with the same superheterodyne circuit arrangement as radios that already used germanium transistors from Mullards, so that it would be familiar to radio manufacturers. The first transistor was operated as a self-oscillating RF (radio frequency) mixer, and the second one as an IF (intermediate frequency) amplifier, which was followed by a diode detector and then the audio stage. The mixer stage was difficult to design (without a computer) because it amplified as a small-signal common-emitter amplifier and also had transformer coupling from the collector circuit to the emitter circuit to generate a large-signal (non-linear) oscillation. It was not easy to choose the turns ratio for the transformer. Eric Zepler would have said “that can be calculated”. When I had calculated it, and had operated the circuit successfully, I asked a man who had worked on the design of germanium transistor radios with similar circuits how the corresponding turns ratio had been calculated. “Calculated?” he said, “we could not calculate it – we used trial and error”.

Having said that, I must emphasise that there were some first-class engineers in the room where I worked at Mullards. On my right-hand side was Barrie Gilbert, a promising young man who in later life was to become one of the leading designers of analogue integrated circuits in the USA. On my left-hand side was Henri Kemhadjian, who was to follow me to Southampton University in 1964, where I became a Lecturer in Electronics in October 1959.