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Old 31st Dec 2022, 5:10 pm   #7
Cathovisor
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Join Date: Dec 2022
Location: Peterborough, Cambridgeshire, UK.
Posts: 418
Default Re: What did I get myself into? Murphy A40C.

It's also missing the original speaker.

The knobs are, L-R:

Upper row - on/off volume, tuning, SW band preselector
Lower row - bandwidth/tone/noise suppression, waveband.

The SW preselector comes into play when you set the radio to SW: you preset the band you want to listen to using this control, then tune along that band using the main tuning control - this is achieved by feeding the output of the preselector into the main tuning circuits. It's a sort of dual-conversion set as a result but has the advantage that because of how it works, the AFC works on short-wave as well.

At first sight of the circuit the set appears very intimidating but in reality it breaks down into easy blocks; the main receiver, the SW converter (also used in the A36), the side-chain IF and the AFC/noise suppression circuit. From personal experience, the trimmers on these sets have a fixed capacity in parallel with the trimmer and the fixed part has a tendency to wander in value: they are set in a sort of cement in the bases of the coils. However, standing the bases of the coils in methylated spirits dissolves the cement completely.

As always, I would recommend Dave Grant's Murphy Radio website for more information: www.murphy-radio.co.uk

Last edited by Cathovisor; 31st Dec 2022 at 5:17 pm.
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