|This set was probably made in 1937 and had been home for a family of mice. These had run off and left their food supply in the lower part of the cabinet. During their stay they had unfortunately sampled the delights of the insulation from the cable to the loudspeaker. When the covering over several inches of lead had been digested, or taken away for bedding material, the cable was left in a very vulnerable condition, because this being a mains energised type, had included some nasty voltages. The last time the set had been turned on there must have been a display of pyrotechnics which caused the denizens to abandon their lodgings in a bit of a hurry (hence the supply of rather stale and uneaten breadcrusts). The most serious resulting damage was that the speaker energising coil was open circuit rendering the unit useless.|
The chassis was completely covered in dust, and although the set has been stored in a damp environment, because of this, there was no rust and the dial mechanism, although devoid of lubrication, was undamaged. The valves are unusual, being the Ct8 type with side contacts rather than the usual pins. The AZ1 rectifier has been replaced and is 100%; the ECH3 showed emission readings of 55% and 80% for its triode and multigrid sections respectively; EF3 95% and the EBL1 60%. Over the years several components had obviously been replaced and all the resistors measured up well but many of the capacitors were leaky and had to be replaced. One of the coils was broken off its mounting and the tuning capacitor, which is mounted at an odd angle to the chassis was very loose because its mounting rubbers had perished. The flywheel was graunching on the chassis because of this but once the various bits had been replaced and the surface of the flywheel cleaned up (because its back acts as a reflector for the back of the dial) the mechanism worked well. I fitted a pre-war "Tannoy" 8 inch speaker and a high wattage resistor to emulate the smoothing action of the old energising coil. Heatshrink sleeving repaired the damaged speaker leads and a modern mains lead and 13Amp plug completed the major work.
Testing revealed some more problems. The EBL1 was badly microphonic preventing the volume from being turned up beyond a whisper. This condition is probably brought about by the mechanical connection to the control grid inside the glass envelope being loose. The expedient solution was to fit a 6V6 after fitting an international octal socket.
The IF coils had aged, and as there was no method of adjustment provided, I had to fit small capacitors to bring them back to their original 462kHz.
I drilled a small hole in the case of the volume control and squirted in some switch cleaner to sort out crackly operation.
After adding a new 100uF smoothing capacitor the residual high level of background hum dropped to an insignificant murmer. Originally the smoothing choke built into in the speaker would have been adequate to deal with this but the new arrangement of a simple resistor needed help.
After refurbishing the cabinet, which had suffered from damp, by rubbing with emery cloth soaked in linseed oil, the set not only looked good but gave extremely good results with only a short length of wire poked in the back.
|The contacts of a small microswitch, operated automatically by the cassette mechanism, had become tarnished and prevented power reaching the deck. Once switch cleaner had cleared this problem the drive belt was found to have perished. There are several potential types of failure here; first the belt can become stretched and shiny and will slip; secondly the belt can develop small cracks along its length and eventually break; thirdly a dreaded disease can affect it turning the rubber into a soft black putty-like material which eventually can just drip away. The first two problems one can expect but the third is most peculiar. I've heard that it can result from too much ozone in the air but I'm open to ideas. Idler tyres can also go this way and it can take ages removing the tar-like residue from adjoining bits of mecahnism before a new belt can be fitted.|
This 1953-54 set has 5 valves and nine wavebands. The UCH42, UF41 and UY41 all tested OK but the UBC41 and the UL41 were poor. A previous repair had been carried out and to my surprise the audio coupling capacitor was leak-free. The set had three observed faults: the mains on/off switch had a lazy action; the medium wave oscillator coil slug was missing resulting in very poor medium wave reception and the IF and RF circuits needed realigning due to component aging. In addition one of the two 1Amp mains fuses was open circuit.
The mains switch was integral with the tone control potentiometer and the mechanism had become worn. After dismantling and bending the operating lever and lubricating, it worked perfectly. A new tuning slug sorted out medium wave calibration and a complete re-alignment made the receiver very lively. The valves with poor emission still work sufficiently well to warrant their re-use. I fitted a new mains connector and lead and wrote out a warning about the live chassis and not to use the set without all its knobs in place etc.