Cossor 348 The next total renovation?

[boater sam]

    Another purchase for renovation Cossor 348.

Dirty; pealing black finnish; old plug but seems to be all there.
I Have the Cossor sheet somewhere.
Any pitfalls with these?

[Geordie McBoyne]

Cossor 348,   TRF or superhet?  I have somewhere a Cossor set which is a TRF on medium and long waves and a superhet on short waves.    The output from the frequency changer is converted down to something like 1Mc/s.   The hexode section of the mixer section of the 41STH serves as an RF amplifier on MW and LW.

Geordie McBoyne.

[boater sam]

Hi.
MW and LW TRF with reaction but S/het SW.
Thats the one; with volume control in the mixer cathode. shunts the signal to ground and alters the bias.

Its going to need a lot of work.

[boater sam]

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seemed little that had been messed with other than the electrolytic block is missing from under the chassis having been replaced by a pair of 32uf Hunts "Tom Thumb" caps which are OK.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.........................

[boater sam]

            Cabinet stripped and first coat of oil, looks better now!

Chassis dusted off and working well. need to do the tuning support plate, its very dirty.

Some pix to be going on with......

[Radio Fixer]

Personally I wouldn't bother with the woodworm killer if there is no evidence of occupation. Kept after the Danish in a warm dry place not much chance of any coming back.

Chassis doesn't look to bad and should clean up OK. Always find those cam operated wave change switches unreliable. Work for a while after DeOxit but a couple of years later need doing again. Come to think of so do most rotary switches except nearly all Philips. So many sets now have wipers with no plating left on the brass . Have thought about getting new switches made for the best sets by Blore Edwards but it may not be possible for some.

Have fun

Gary

[boater sam]

Didn't find any worm at all, in fact I seem to do very well with my sets, only ever bought 2 with any signs of worm. Still give them all a dose of killer though, perhaps I'm adiced to the solvent.

I would doubt that there was ever much plating on the switch contacts. the wiping action would soon wear it away. I can't decide what the bobbins are made from, it looks rubbery but is hard and very black. Ebonite?

[boater sam]

            I had to give up with the speaker fabric. After being washed it was still so discoloured that short of bleaching it to destruction I could see no way to use it again. 83 years of nicotine and coal fires sometimes cannot be reversed. Its place mat speaker fret again.

Made a box for the new capacitors to replace the Tom Thumbs which are too large a value according to the service sheet, reservoir is listed as 4uf, not 32uf! New stock on the way from the Far East. I will use 10uf reservoir and 20uf smoothing in the box, kinder on the rectifier.

Cleaned off the chassis, that's all it is getting, no Brasso on this one. Cans came up well.
Papered the dial back plate rather than paint, its easier to do and easier to replace.