Vidor Model CN243 "All Wave Bandpass" Receiver

 Quite a compact set from 1934 for AC/DC mains, meaning it has no mains transformer and the possibility of a live chassis if the plug is wired wrongly. When it came from the factory any exposed metalwork would have been insulated from the user but after over 80 years this precaution has been breached. The knobs are secured by metal grub screws and all these are visible. Although they may have had a wax filler this has long gone and has not been replaced. I notice that the loudspeaker is held in place by four screws with decorative heads which I imagine could well carry a connection to the mains unless the speaker metalwork is isolated from ground.

 

 When I removed the wooden rear cover I found this. The old smoothing condensers have been replaced. The tall wirewound component on the right is a dropper so that the valve heaters can be driven directly from the mains supply.

 

 Alas, the label is badly damaged. This is because the set has been home to mice.

 

 Here's the evidence... the remains of their favourite food.

 

 
 A three-gang tuning condenser. This means that the tuning coils must be very accurately matched so the alignment across the wavebands is maintained.

 

 The dial is going to need careful handling because it seems to be thick card mounted on a metal backplate. It shows three wavebands which I think is pretty unusual for a TRF receiver. The later superhet receivers which followed the TRF design were much easier to align and a short waveband was no trouble to align because the local oscillator could be adjusted to keep in track with dial markings. Once cleaned I'll be able to work out the exact date of manufacture of this example because the wavelengths of the stations listed on the dial were in a state of flux during the first half of the 1930s.

 

 The set is now fitted with the following valves.. RF amplifier Mazda VP1321, Detector Mullard SP13C, Audio Output Mullard CL33 and HT rectifier Cossor V8. The rectifier is on a B5 base and the CL33 is an IO whilst the other two are B7. I suspect the rectifier valve was originally a 1D5. All the valves are fitted with higher than usual heater voltages and are designed to be run at the specific current of 200mA defined by the wirewound dropper resistor you can see in previous pictures,

 

 There are several clues to the model number of this radio. The label stuck to the inside of the case, the bottom edge of the dial and this label fastened to the rear of the chassis.

I don't have the service manual for this model as it seems to be too rare but I have something similar which you can see if you click the label.

 

 Now, some views under the chassis..

 

 The three-position wavechange switch.

 

 RF amplifier tuning coils.

 

 Aerial tuning coils..

 
 

 

 
 

 Pictures of the dial which was very grubby because it's made from a coarse finished cardboard.

 
 

 I wasn't going to test this set electrically at present but I wanted to make it look presentable which meant cleaning it up and replacing the torn speaker cloth. After removing the chassis I cut the speaker wires because these are rubber covered and very brittle so will need replacing before the set can be used. I then detached the loudspeaker and pulled off the old cloth.

 

 I have some spray-on adhesive which I find is perfect for refitting cloth, then I refitted the decorative screws and the original gasket and the loudspeaker.
 
 
 The dial glass was opaque so I cleaned it and used brasso followed by polish. This removed blemishes and most of the yellowing.
 

 The set is much improved, at least in looks.
 

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