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Old 19th Jun 2019, 5:15 pm   #1
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Join Date: Jul 2010
Location: Royal Berkshire, UK.
Posts: 379
Default Cossor 501AC 'Melody Maker'

Known in our house as ‘The Snowman’ set, owing to the title of Raymond Briggs festive film from my childhood, where such a set makes a brief appearance. The film, introduced by David Bowie, twenty seconds in, and there in the attic, left of David, a Cossor Melody Maker.

Having always liked the idea of such a set & long before I was into radios, how did I ever buy one, not knowing which make or model to seek? eBay! Whilst looking for a British set to revive, at the bottom of the screen some pictures of other sets under the ‘you may also be interested in these’ banner. Sure enough, I recognised the set immediately, this also gave me a make and model number to go by.

Many years later, after seeing these sets sell for more than I was willing to part with, or typically, too far away to collect and not wanting to risk postage, one was finally listed and was only a short drive away, another bonus being, the sole bidder.

The set belonged to the sellers’ mother; she had it from new and was used up until the mid-60’s, where it was then placed in a cupboard, only seeing the light of day again in 2017. The seller didn’t recall any previous repairs, but as he said, he was only a small boy back then but remembers the set being put to good use in the kitchen.

Quite possibly the fluffiest chassis ever to grace the bench, it had indeed been ‘preserved’ by cooking oils, plus a good layer of fluff. The only non-original part, the dial lamp, which being rated at 12 volts, was incorrect for the set, but would have lasted many years more!

First things first, remove the rear cover & check all the coils (including the ‘speaker) plus transformers for continuity, then onto the switches, resistors and capacitors. The mains lead was original, but dangerous & leaving debris all over the bench. Removing the mains lead from the set revealed the lead was dead-short, as the internal rubber insulation had failed in a number of places. Checking the chassis over proved the set was a worthwhile repair, thankfully, the cabinet was cosmetically complete too.

Whilst the HT capacitor was reforming, which came back remarkably well over a period of a few days, the cabinet was given a buff outside, with a jolly good going over inside, and the four knobs needed a stiff brush to remove grime from the knurled bits. The bezel, which is out of shape and was very loose, amazingly the remaining spire clips were either amongst the fluff, or attached to the speaker magnet. Once the cabinet had been cleaned, the bezel was secured with the original spire clips plus a spot or two of Araldite, to ensure security.

The speaker cloth was a mess, not only did it have some holes, but had over the years ‘absorbed’ the kitchen atmosphere. Cleaning just made things worse. The only answer was to re-cover. Looking around, ended up at Dunelm where they had some cushions knocked down to £4, sure enough, the speaker cloth of my Melody Maker came from a cushion.

With the cosmetics coming together, I ventured into cleaning the dial glass. Having the voices of other people’s experiences with such things, the outer side of the glass had to be cleaned with Cif, as it was caked in grease; the inner part had a light film. Trialling an area of the dial glass which goes un-noticed when assembled revealed ‘optical instrument cleaner’ from RS removed the film, but not the silk-screen! Phew … the correct lamp now fitted too. The whole chassis at this point was then given a good dusting off, but I left the light oily film, which has protected the internal metalwork very well over the years.

Time for a temporary mains lead, the original output valve grid-coupler removed & a modern replacement ‘tacked’ into place, slowly with the Variac-volts the set crackled into life, hmmm. Powered down, then used some switch cleaner on the potentiometers, the waveband switch, valve holders & gave the valve pins a good clean until shiny, the reward for this was glorious sound on all wavebands, well, glorious in that we had sound at all, albeit, quiet and distorted.

Checking around against the datasheet I have, showed a number of supply lines were down, owing to resistors going high, the 25uF output valve capacitor being leaky plus the rest of the waxies acting more like resistors. Being original waxies, I decided to re-stuff them, madness I suppose, must be the solder fumes!

By the time I had replaced the out-of-spec resistors (all 4 of them) and re-stuffed the waxies, the new mains lead had arrived, which closely matched the original. Not happy with the security arrangement of the original mains lead, I made good use of the available hole next to the mains lead entry point, and secure the new lead with a P-Clip.

Other modifications include:- silver tape down the sides & along the bottom of the dial glass, to ‘bounce’ the light around a bit more, capacitor across the power switch to remove the ‘pop’ through the ‘speaker when switching off and spots of Araldite to better-secure the bezel.

All in all, a pretty easy-going repair, lots of elbow room, no live chassis to worry about and the alignment is so good, it’s not worth trying to re-adjust.
The set has been used regularly since the work and performs pretty well, all the better when used with a long bit of wire. The restoration came together rather quickly in the end.

Some photos to following, painting many more words.

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Slowly turning the 'to-do', into 'ta-dah'
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