The A.J.S. Table Receiver from 1923 - Inside Out


The A.J.S. table model from 1923 uses the company's first T.R.F. receiver, which has many features that are commonly found in early British designs. As with most receivers of the day it has a lot of controls to adjust and easily accessible valves. The four valves are bright emitters and so the filament supply current is very high when compared with later receivers using dull emitters. As an example, a typical valve of the period, the L.S.2 has a filament voltage of 6 volts and a current of 1.5 amps, so each filament alone consumes 9watts. The valves have a relatively short life of several hundred hours, and when new sold for a few pounds. At the time this was a large sum of money when compared to the average weekly wage, and so valve radios were very much a luxury item.

Each valve filament is fed via a variable resistor which controls the emission, and so varies the gain of each stage. It also can extend valve life by running the filaments at a lower voltage. A valve switch is incorporated so that fewer stages can be used when receiving strong local transmissions, or when using headphones. This saves battery power, and also extends the life of the audio amplifier valves, by using them less frequently.

The receiver has a tapped aerial tuning coil for Medium Wave, and a second plug-in aerial tuning coil for longer wavelengths. The tuned interstage coupling transformer has to be changed for optimum reception on the longer wavelengths, and as a result it is a plug-in component. Different versions were available for different wavebands.

A view of the receiver, a typical pre-1926 A.J.S. product. The receiver shown in the photographs can be found at the Olens Radiomuseum in Belgium.

All of the components except for the valves, the interstage coupling transformer, the control knobs, and possibly the screw terminals, and variable resistors, appear to have been made in-house. Some of them carry A.J.S. patent numbers. The choke coupled audio stages were always a feature of any A.J.S. receiver that had more than two valves.

The underside of the top panel.

The aerial tuning capacitor.

The photograph on the left shows the tuning capacitor for the aerial tuned circuit. It carries the A.J.S. patent number and was the most common type of tuning capacitor used by the company.

The on/off switch on the right of the capacitor is a typical A.J.S. switch; examples of which can be found in all of the company's receivers, other than the later Symphony range.

The reaction coils are very different to the ones used in later A.J.S. receivers, and are of a much simpler form of construction.

The reaction coils.

A close-up view of one of the reaction coils.

The photograph on the left shows the moving reaction coil. It is mounted on the end of a short arm that is attached to the reaction control shaft. When the shaft rotates the two coils are brought closer together so that feedback will occur. A contact is mounted on the arm to short circuit the coil when reaction is set to minimum.
The photograph shows the audio coupling chokes that were used in all A.J.S. receivers with more than two valves.

The audio coupling chokes.

A.J.S. carbon resistors.

A close-up view of the sockets for the plug-in coils.

The upper socket for the Long Wave coil contains the plug on the right, which when inserted short circuits the plug-in coil. It acts as a Long Wave/Medium Wave switch and also allows the receiver to function when the coil is not inserted.

The lower socket is for the plug-in Neutrodyne H.F. coupling transformer. Different coils were available for different wavebands.

Above the socket is a plug-in link labelled reactance. The reaction control and built-in reaction coils are for Medium Wave only. Presumably a plug-in coil was available for Long Wave reaction.

The coarse aerial tuning switch. This early type of switch was not used in any of the later A.J.S. designs.

A final view of the internal circuitry.     

Circuit Diagram

The circuit diagram.

The receiver is a 4 valve T.R.F. design with a tuned high frequency amplifier, a detector, and a two-stage audio amplifier. It covers part of the Medium Waveband and Long Wave, or other wavebands using suitable plug-in coils. The two audio stages can be switched in, or out, as required to reduce battery consumption.

Circuit Description

High Frequency Amplifier

A simplified version of the high frequency amplifier.

The aerial tuned circuit consists of the tapped Medium Wave coil, the plug-in Long Wave coil, and aerial tuning capacitor A.T.C. The Long Wave coil socket contains a shorting plug to short circuit the coil when the receiver is used on Medium Wave, or when the Long Wave coil is not inserted in the socket. There is an external link between the aerial terminal and the 'R' terminal so that an A.J.S. Patent Rejector Circuit can be used with the receiver to remove unwanted signals.

The taps on the Medium Wave coil and the A.T.I. switch provide coarse tuning. No attempt is made to match the aerial into the tuned circuit, which must have been severely damped, or detuned by the long wire aerials in use at the time.

The output at the valve anode is tuned by C2 and the interstage coupling transformer. This plugs-in to allow other transformers to be used for different wavebands.

The valve is biased by potential divider R1 and R2 across the low tension supply. The bias voltage is decoupled by C1.

The variable resistor in series with the valve filament allows the gain of the amplifier to be adjusted. As no attempt is made to neutralise the valve's internal capacitance, it's likely that the amplifier could be unstable at certain frequencies. This would depend upon the type of aerial used and the setting of the variable resistor.


The detector is a conventional leaky grid detector, directly RC coupled from the interstage coupling transformer H.F.T. The valve is biased by the leaky grid coupling components C2 and R3, and the potential divider across the low tension supply, R1 and R2, which is decoupled by capacitor C. The positive voltage from R1 and R2 biases the valve to improve the linearity of the detector to minimise audio distortion and provide a high quality output. The remaining carrier wave at the output is filtered out by C3.

The variable resistor in series with the valve filament will alter the gain of the detector and also its characteristic. A high gain might be useful when receiving weak signals.

Medium Wave reaction is provided by the two ‘basket wound’ coils, L1 and L2. The reaction control moves the coils closer together to increase positive feedback until oscillation occurs. It also includes a pair of contacts to short circuit L2 at minimum reaction, so that no feedback will then occur.

There is a plug-in link on the panel next to the Long Wave coil. This allows an external reaction coil to be plugged-in for Long Wave operation. It will provide positive feedback to the input of the high frequency amplifier via the Long Wave aerial coil.

A simplified version of the detector.

The output is connected to the valve switch so that it can be directly connected to a pair of headphones in two valve operation, or be connected to the first audio coupling choke when the audio amplifier is in use.

Audio Amplifier

The audio amplifier without the valve switch.

The first audio amplifier is choke coupled from the detector by L1, C1 and R1. Similarly the audio output stage is choke coupled to the first audio amplifier by L2, C2, and R2.

C3 which is in parallel with the loudspeaker or headphones helps to maintain a constant anode load at all audio frequencies. This is because the high impedance loudspeakers and headphones are predominantly inductive and so their impedance is more or less directly proportional to frequency.

The variable resistor in series with each valve filament varies the gain of each stage and can also be used to reduce the current drain from the low tension accumulator.

The loudspeaker positive terminal is directly connected to the HT3+ terminal on the back panel, so that the audio output can, if necessary, be supplied from a higher voltage to provide a higher audio output.


Another view of the receiver.

A final view of the receiver.

All of the photographs were kindly supplied by Joris Van Campenhout of the Olens Radiomuseum in Belgium. We thank him for all of his help in producing this section.

We would like to add technical details of other A.J.S. receivers, if anyone can help please email the webmaster.

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