RA117E - The ‘One-Transistor’ Radio

January 2015 …

RA117E N0586 was given to me as a non-working receiver. Its previous owner generously passed it my way in the knowledge that I would almost certainly find the fault that had eluded him for a very long time. Little did he know, but I was about to identify not one fault but no less than thirteen faults … four of which had been with the receiver since it was manufactured back in December of 1965!

I decided that this would be my New Year’s treat … get the ‘One Transistor’ Radio working. It was ‘stone deaf’ and only occasionally was it possible to receive the strongest of local MW signals. The logical approach was to strip it down to its individual modules and test each one in turn after refurbishment. That way, I would be sure to come across the illusive fault.

Unlike my plain-vanilla RA117, this E-variant had already received the approved PSU resistor upgrade. Note the black metal-clad resistors bottom left and centre and the large gold coloured 9K resistor.

The remaining carbon resistors and tubular capacitors were replaced with modern types and the PSU smoothing pack was re-stuffed with a pair of 33uF/450V capacitors.

Testing the PSU and audio circuitry is easy. The audio stages were working fine but a higher than expected voltage drop across the main smoothing choke, L80, indicated that something elsewhere was not right.

PSU/Audio compartment before and after