[ukcol]

I have been looking at the circuit of the Armstrong "London Stereo Twelve MKII." This is an AM/FM stereo receiver chassis that uses no less than three ECC85s.

One ECC85 is used for the usual RF amplifier and mixer functions in the VHF tuner. One is used in the stereo audio pre-amplifier. Half on the last ECC85 is used in the VHF tuner providing AFC.

The remaining half of the last ECC85 is used in the AM detector. A hand drawn copy of the circuit is attached below. The triode is used as a buffer RF amplifier to feed the diode type AM detector.

I assume, in my ignorance, that this arrangement reduces distortion by providing a larger voltage swing to the input of the detector diode and that it has a better performance at high modulation depths. What does the team think?


Details of this chassis, including the circuit, are available on the Radiomuseum web site.