On the strength of the X-10, Sinclair Radionics won a contract to supply vibration test equipment to an aircraft equipment company; a high-powered amplifier which would drive a vibrator with power output up to 120 watts. Clive Sinclair was busy feeding ideas to Jim Westwood to try out. Richard Torrens was busy trying to solve some problem that had been encountered with the transistors which had been shipped to Hong Kong. Another engineer had to be found, since the Hong Kong problem needed someone's dedicated attention, and the deadline for the 120-watt amplifier contract was looming ever nearer.

So desperate was Sinclair that he nearly sent Torrens to Hong Kong - until he found Martin Wilcox, who joined the company as chief engineer in February 1965. His first job was to sort out the 120-watt amplifier contract. After Sinclair had left for Hong Kong, Wilcox decided that the prototype amplifier couldn't possibly be ready in time for the client company's engineer who was visiting in a few days. He therefore set to and designed, built and tested a conventional 20-watt amplifier to demonstrate instead. At least there was something to show; he carried on and four months later the Z-120, as the larger amplifier was called, had been developed and tested. Built to a military specification to be acceptable to the aircraft industry, these eventually sold for £75 each.