The A.J.S. Symphony Two Receiver - Inside Out


From the 1926 Symphony catalogue.

In 1926 A.J.S. launched a new range of receivers which were much simpler to use than the previous models. The recently developed dull emitter valves had a comparatively long life, and so didn't have to be as accessible as the older bright emitters. Everything except the loudspeaker or headphones is enclosed in the case, including the batteries. A range of interchangeable plug-in coils was available for different wavebands. The coil, and the aerial and earth connections are accessible via the left-hand cover on the front of the receiver. The right-hand cover gives access to the batteries.

The Symphony range of receivers was very modern looking for 1926. A.J.S. hoped that the new receivers would allow sales to return to their previous high levels.

The receiver, including valves, loudspeaker, and batteries sold for £17.10.0d. It was the cheapest model in the Symphony range, but still relatively expensive as it approximates to around £900 in today's money.

Circuit Diagram


The two-valve receiver is a TRF design, the first stage consisting of the aerial tuned circuit, reaction circuitry, a leaky grid detector, and an audio coupling transformer. The second stage is the audio output amplifier which drives an external high impedance loudspeaker, or headphones. Six-Sixty dull emitter valves are used, along with A.J.S. capacitors and coils.

The tuned circuit uses a standard A.J.S. centre-tapped plug-in coil (L1), which is simply connected to the aerial by C1 (Aerial 2), or directly via Aerial 1. As a result the aerial will have a loading effect on the tuned circuit, altering its frequency. The tuning capacitor C3 is a standard A.J.S. component, as is the reaction capacitor C2. The first stage is a conventional leaky grid detector, biased by C4 and R1. The centre-tapped aerial coil allows positive feedback to be applied from the anode via C2.

L2 has two uses. It acts as a radio frequency loading coil, allowing positive feedback from output to input via C2 and L1, for reaction, and also acts as a filter, to filter out the carrier wave and any RF components from the audio output.

The audio output is transformer-coupled to the audio amplifier V2 which is biased by the grid bias battery. The output is connected to a jack socket where an external high impedance loudspeaker or headphones can be connected. The jack socket also acts as the on/off switch by switching the low tension supply. C5 is connected across the output to flatten the frequency response, compensating for the inductance of the loudspeaker or headphones.

The receiver removed from the case.

The underside of the chassis.

The rear of the chassis.


The front of the chassis.

More views of the receiver:
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