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Cossor 348 radio, another fine mess I got into.

 
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Joined: Sun Apr 13, 2014 2:47 pm
Location: Middlewich, On the canals, & Philippines

Cossor 348 radio, another fine mess I got into.

Post by Boater Sam » Sat Apr 16, 2016 7:49 pm

Bought as a challenge, has a dirty but intact speaker fabric, good celluloid tuning scale and cover glass in its frame, all the right knobs, undamaged back, but it looks horrible, dark and scratched with bald patches.
After a good look around and separating a few rotted rubber wires there seemed little that had been messed with other than the electrolytic block is missing from under the chassis having been replaced by a pair of 32uf Hunts "Tom Thumb" caps which are OK.
I would like to find a picture of the original so I can recreate the box if anyone could oblige please.
Fabulous mains/waveband switch, a real work of art.
Checking valve filaments showed the output 41MP to have an intermittent filament, not the solder on the pins, but with a rap I got continuity. How long for is in question.
Mains and output transformers checked out OK as did the energised speaker. Some small cone damage, spotted it with glue to stop it getting worse, it is centred OK. No shorts on LT or HT
Rewired the dial lamps wiring (both worked!) with a bit of old mucky white pvc and the 3 speaker wires with cotton covered wire to replace the rubber horrors, sleeved the top cap lead to V1 , decided that the mains lead was serviceable, and gave it the beans.
Nothing but crackles when the tuner was moved, could see lots of blue sparks in the air gaps of the oscillator section so washed it out with IPA and a brush. When it had dried was rewarded with sound on all 3 wavebands. The volume control was noisy but on opening it discovered that the wiper presses a continuous metal strip onto the track rather than making direct contact. A quick scrub with a pencil on the track brought about an improvement.
No top notes so removed the tone corrector from across the output transformer primary. A 1000v componant, not leaky at all!
Short wave not brilliant but the set is working as a superhet on short wave, local oscillator is running. MW & LW work well if the reaction control is adjusted, its a TRF on these bands.
All voltages seem about correct, checked on the 4 waxy 0.1uf caps and they all seem to be acceptable, most of the caps are bakelite mica blocks and all are fine. Even the high value resistors are within 20% of the marked values. Terrible job to lift one end for checks as it is put together like a birds nest with those infuriating wire wrapped and soldered connections all over the show. But its 82 years old so they got it right even if it is difficult to work on. Minimum disturbance and meddling, its got to retain its originality, warts and all. Just blow off the fluff and dust, no polishing of chassis or mass component changes.

So leave it running while I looked at the cabinet which is horrible. Someone has refinished it with treacle brown varnish on top of the original light polish so the whole lot has to come off, much paint stripper turned it into a sticky black goo but it stripped eventually. I will sand lightly and treat it with worm killer anyway though there is none at all, and finish with 4 coats of Danish oil. A little bit of veneer is required on the front bottom edge, otherwise it is very good.

More and some finished pix to come.........................

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