Cossor Empire Melody Maker Model 234

 I understand that this was a kit radio available as a complete set of parts, but since its first assembly it's been overhauled.. perhaps in the early 1950s because of the plastic covered wiring? I imagine that little monetary value was given to the set and it was just updated to provide someone with a working receiver otherwise wiring would have been replaced with something from the correct period. The pentode RF valve has been replaced as well as the LF output valve.. the former, which looks pristine, carries a military arrowhead.

 

 Below a view under the lid of the case. A pair of similar looking coil cans marked FC1109 and FC1110.

There's a Cossor interstage transformer, several controls and a few other parts.

Most of the original wiring is rubber covered and in poor condition.

 

 The left side has aerial and earth connectors and adjacent a selectivity control. At the bottom is a small rounded knob which is the long/short wave switch (actually what today we understand to be long and medium waves). The knob, which can be pushed in or out, connects to a metal lever screwed to a pair of toggle switches mounted in the base of the coil assemblies. Each switch merely shorts out the additional coil fitted for long wave reception.

 

On the right of the cabinet is a pair of terminals for loudspeaker or headphones. These will carry HT and will be designed for high impedance output. Early speakers and headphones were usually high impedance.

 
  This is a solid dielectric 0.0005uF variable condenser used for adjusting the aerial. This control allows the user to trade off overall output versus selectivity, a vital adjustment if one lived close to a powerful transmitter. Two aerial connectors are used.. one connecting to the selectivity control and the second bypassing it.

 

Here's a home made grid bias battery made from what appear to be two 4.5 volt bell or torch batteries. The sockets from an old bias battery have been re-used.

 

 Behind the front panel are these three controls. Top, the on/off pull switch; left a solid dielectric reaction control and right a volume control which merely allows for a reduction in the filament voltage of the RF amplifier.

 

 The receiver has two RF tuned circuits. Because of the difficulty of precisely matching the coils as well as accommodating different values of stray capacity, the user is presented with two independent tuning controls. These must be kept roughly in step whilst searching for a broadcast but, once one is found the pair, together with the reaction control, need to be fine tuned for best volume and clarity.

 

 The tuning condensers have oddly shaped vanes. This is to provide a linear tuning scale. The shape conforms to a logarithmic design.

 

 Here's a picture of the coil under the can marked FC1109. Slightly puzzling was a side connection on the can which was wired to an adjacent fixed condenser. To save a minor complication in wiring one of the screw terminals holding the can in place has been used for a coil connection.

 

 A picture of the fuse fitted in the HT/LT negative lead. This is a standard screw in type of bulb and is marked Empire 2.0V.

 

 Below... you can see a glass component looking like a modern fuse which is actually a fixed resistor. The pip shows that its in a vaccuum. It seems to be a half megohm grid leak for the LF amplifier. It's in series with the grid connection and such is the extremely low value of grid current the signal voltage drop across the resistor is negligible.

 
 

 

 Here's the manufacturer's label. I examined the valves and found the RF amplifier is a Cossor 220VSG pentode with a B4 base and marked with a military arrowhead (so will be WW2 surplus from the 1940s or 50s), a Cossor 220P (a triode with a B4 base with a vertical style electrode assembly and carrying a paper label with "2.2mA/V 100%") and a PM2 (a triode with B4 base marked "Mullard Radio Valve", "BVA" and a large "2".. plus "Protected by patent" with two large letters underneath.."ZA" and on the opposite side the letters "PM2" and the early Mullard Aerial-Earth logo). This PM2 has an early horizontal electrode assembly.

A previous owner has put the PM2 in the LF output stage and the 220P in the LF amplifier position.

Below is the circuit diagram

 

 

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