Failure, Cossor RIP, Oh Dear!

[Boater Sam]

Not beaten often but today has been a waste of time. And a few components.

Cossor 494, Melody Maker, 1947, £15 when new.

Good Bakelite case and back. Complete with a few repairs obvious but not bad. 1 wrong knob. Cloth dirty but whole. Transformers have all the windings intact and no shorts to ground.

'Orrible clear plastic thin mains flex, knot strain relief, 13a fuse of course! Can't do with that so chassis out onto the bench, 3 lengths of screwed rod fitted as chassis legs so that I can turn it over and work underneath, a length of 3 core, strain relief made and bolted, 1 Amp fuse, earth to chassis, shop speaker plugged in.
Remove the undamaged tuning scale glass, had to cut 2 of the rubber corner mounts, all 4 had turned into coal.
Tuning cord (2 bits of string) busted so I sat and enjoyed restringing it. Plenty of fluff and spiders so a blast on the air cleaned it up.
7C5, Output valve cathode decoupler leaking, grid coupler failed on the megger so replaced those.
Wiring OK, nothing obviously terrible so on the lamp limiter, huge hum, restuff the electrolytic can, hum gone. But nothing on the speaker, no crackles when changing waveband. Finger on the volume control wiper, nothing.
Finger on the output valve g1, a good hum so measure the 7C6 DDtriode anode, very high, nothing across the cathode, ha, no filament, that will be it then!
Search stock find another with rusty pins ( why do locktal pins rust worse than any others? ) stick it in, full power, and we have signals, weakly, on all 3 wavebands. Excellent progress, that's a hour so far, not bad.

Audio is up to general power level with finger at grid of 7C6, volume and tone controls work as expected. Lack of volume seems to be due to RF side before detector, time to check all valve voltages.
Agh! turning the chassis over with power on brought a massive blast of radio 4. Now, I've had this before. I know what it is but have that sinking feeling.

Its the cores in the IF transformer that have fallen off the adjusting brass bits.

Remove the IF transformers completly as they are the ones with the can turned under to bodies and can't be opened in situ.
A shake proves that both have loose cores. Carefully de-wax the adjusters and opening them lets all 4 cores fall out!
All the core tops were broken up due to too much wax being poured in when it was built and the twiddler has had a go to "tune it up".
Gluing them back on is very fiddly but possible, so mix a bit of epoxy and become frustrated trying to hold them in line with tape.
I decided to have a look at the transformers whilst the glue started to set and could have wept. All the very fine wire ends soldered to the vertical wires are rotten and green, 2 broke off just touching them.
The windings are in pot cores and are rotten through and through, its surprising it ever made a sound. Damp over the years and the flux when they were soldered has ruined them.

Now, I like a challenge but even if I spend hours re-winding them, reassembling, gluing cores on and struggling to get them in line again I still only have a 70 year old Melody Maker ( I have 7 anyway ) which is no way rare or desirable which will need re-aligning possibly breaking the cores off again in the process. Chances are that the oscillator coils will be bad too.
Time to call it quits, use the bits as spares and preserve my sanity.

Time for dinner, a glass of wine and call it quits. An unusual failure.

Sam.

[Robint 47]

Surprised at you Sam giving in so easily' seen some of your previous replies.

For a Cossor I would try and find an old pair of IF coils and try them with a little tweak maybe but for an old Cossor(I think they are one of the greatest) anything is worth a go.

Robin.

[paulsherwin]

I also don't share the common reverence for Cossor sets.

It's never nice to see an old radio scrapped or butchered, but sometimes they're beyond help. This sounds like a good candidate for replacement of the functional parts of the chassis with a Bluetooth module and FM chip, plus a standard op-amp audio amplifier, though you could retain the valve amp. The heater supply could provide power.

Radios 'restored' in this way and in good cosmetic condition sell for big bucks on eBay.

[Karen O]

Might it be possible to hide modern replacements inside the IFT cans?

On second thoughts, IFTs suitable for valves will likely be as large as the ones that are already there...

It's sad when key parts like these scupper a repair.

[Boater Sam]

These cans are small to start with, about 30mm square and 65mm high.
There is only so much patience and time I can apply these days.

Interesting idea to upgrade it but I know nothing about bluetooth etc., is it simple? Can an FM front end be fitted and use the tuner?
Sam.

[Steve_P]

Get to a radio rally and look in the trays of old parts. It's amazing what you find.

Cheers,

Steve P.

[Boater Sam]

That's what would worry me! Difficult to tell if they are OK when standing in a hall.
No, its the end, enough is enough. I'll find someone maybe that wants a "Valve sound guitar amp" !
But the pot cores may just enable me to finish the Pennine radio that has been bugging me with its lack of Long Wave. There is a thread of mine about it somewhere. I've got 4 pairs now!
Sam.

[paulsherwin]

Originally Posted by Boater Sam

These cans are small to start with, about 30mm square and 65mm high.
There is only so much patience and time I can apply these days.

Interesting idea to upgrade it but I know nothing about bluetooth etc., is it simple? Can an FM front end be fitted and use the tuner?
Sam.

If you want to pursue this route, look for cheap Chinese modules on eBay. You're unlikely to be able to tune any radio module with the existing tuning scale arrangements, but they often come with a remote control, or you may be able to set up a few microswitches to operate the buttons. An interesting project anyway.

There are modules available with an FM tuner and SD card MP3 player (and remote) for about £3. With a 16GB SD card full of music this would make a great jukebox - much better than the skip anyway

[McMurdo]

Before you do anything drastic I'd put it to one side for a few weeks and see if your determination to succeed comes back. The first time I rewound a corroded transformer (admittedly an oscillator coil) I attacked it as though I was certain it wouldn't even work. But it did, and it gave me the impetus to 'rescue' other radios that were ostensibly too far gone. One is skeptical at the time but a good rest works wonders.

[Refugee]

I have got an old chassis that I saved from the bin a few years ago that has a couple of IFTs on it. They will be totally untested though.

[PaulR]

Could you try capacitative coupling?

[kalee20]

Can you post a photo of the construction?

I've had cores come off slugs in a Pye IFT, I glued them on, lining-up with the slug in a lathe chuck and the adjuster in tailstock chuck. I also rewound a couple of coils. It's a pain, but my conscience wouldn't let me do otherwise!

[crusher19860138]

I've been in a similar situation many times before,i usually put the set away for a few months,getting on with other projects,then come back to it with renewed enthusiasm.

[Lloyd 1985]

I built a radio based on a Cossor circuit, from one of their melody makers, as I had the coils and waveband switch from one, but the IF coils were an odd match, one from a Bush, possibly DAC90 or similar, and a round can one from a Philips! Worked a treat. Maybe if you have some odd IF transformers hanging about you could bung em in to try it!

Regards,
Lloyd

[Boater Sam]

It is very heartening to receive such encouragement from so many, thank you all.
Our summer cruising starts next weekend so it will have to wait till autumn but I may have a go at constructing a Frankenstein radio from the scraps of others lying around.
Yesterday was a really bad day all round. It started badly and got worse when I found my favorite old Adcola iron had expired, suppose finding a new element and tip is a forlorn hope.
Then this IF transformers horror, and then to cap it all a monster Marshall AVT 275 amp turned up for repair. Horrible thing full of integrated circuits and one token ECC83 valve for some daft reason. But if I can't/don't want to fix it the guy will turn it into a coffee table!
Sam.

[Boater Sam]

I have an Ekco U245 chassis that's beyond redemption so I shall try it with those. I'll have to take the damping resistor off the first TX secondary, just hope the cores don't fall off, they are the same construction.

[Keith]

I wouldn't blame you for calling it quits, Sam. Hardly the most attractive radio. I would put it a close second to the Ever Ready Sky Queen in the ugly duckling stakes! (I'll just sit back wait for the flack...)

[Boater Sam]

No flak from me Keith, I agree. The woody ones don't look so bad.
This being a 494 at least the cream trim is not a separate item that shrinks and falls off like the 500 version, its just paint!
Its a fair chassis though apart from the bottom coupled aerial coil arrangement.
Sam.

[G8UWM-MildMartin]

I like them!
I think the chassis from any of the 494, 500, 501 and 520, AC and U versions, would fit the cabinet.

[Herald1360]

Originally Posted by Boater Sam

Yesterday was a really bad day all round. It started badly and got worse when I found my favorite old Adcola iron had expired, suppose finding a new element and tip is a forlorn hope.

Maybe not..... I've got a NOS(?) 25 watt one in original packing somewhere. (In middle of house move at the moment, so it could be either in sister 1's partner's shed near Leominster, sister 2's spare bedroom near Ross on Wye or a storage unit near Bromyard).

See closed parts offered post of 3rd Nov 2014 11:47 pm for details.