Grand Prix Moderne 610

4th September 2008

This set showed some signs of life, the valve heaters were lit and the tuning indicator showed that stations could be tuned in on all wavebands. There was no sound however on either channel. Looking for a common cause, the HT supplies to the amplifier panel were checked and found to be in order and the cathode voltages of the output valves were around the expected figure, indicating normal functioning. The unexpected cause of the fault turned out to be the 220K anode load resistors for the triode sections of the output valves, all four were completely open circuit. Replacements restored the sound but it was then found that the AFC did not work. The AFC system unusually uses a small double triode valve as a DC amplifier and the anode load resistor to one side of this was also found to be open circuit, replacement provided a complete cure. The reason why these five resistors had all failed was not clear, although small high-value resistors with large voltages across them are vulnerable components. [Grand Prix Moderne 610]