The IC-10 was an audio integrated-circuit power amplifier, created under a marketing agreement with Plessey, who were to produce the devices for Radionics. The first batch was scheduled for delivery on 1 June 1968 and the advertising for the IC-10 duly appeared as a double-page spread in all the usual magazines. Deliveries of packaging material and instruction leaflets began on time, and all was set for a June launch.

June arrived - but no ICs: there had been production problems at Plessey. No - they didn't know how long these would take to sort out. No, Sinclair couldn't have even a small delivery immediately - not for an unspecified time.

Since it takes about three months to change advertising, Sinclair decided not to modify the plans, for surely the devices would be available by the time the adverts changed? Eventually, it became apparent that the delay was going to be prolonged, but orders - and cash - were flowing in from customers. The delay was lengthy and it was likely that the customers' payments would have to be refunded, at considerable expense to the company.

Luckily, Chris Curry - later of Acorn fame - was working on the design of a miniature FM radio which contained a small device - the IC-4 - which was wheeled out as a stop-gap alternative to the IC-10. Each customer who had ordered an IC-10 received an IC-4 as a free gift with an apology for the delay and a request to be patient, since the IC-10 was well worth waiting for. Its true worth was, however, definitely a matter of opinion, as Alfred Marks recalls:

It was Clive who first made an integrated circuit available to the public - the IC-10. Then an integrated circuit was a miracle, but the IC-10 wouldn’t peak at 3 watts really, and flopped. It was probable, although only rumour, that the IC-10 was a product which Plessey were not too happy to have in their stable, anyway.
(Sinclair & the Sunrise Technology, p.27)

The IC-10 eventually emerged at the end of 1968 and remained in Sinclair's range until the middle of 1970.