Cossor 494AC

[gary_crutchley]

Hi all,

As this is the first valve set that I have taken from a non-working to an operational state, I thought I would write it up even if it might be a little mundane for some of you. First off I have to admit that I got some assistance from my father with the actual electrical work, he is a retired electrician and actually started out in radio and television.

I bought this Cossor 494AC a couple of weeks ago, cosmetically it looked in great condition, although the case is dull and will require a good polish. Electrically it looked original, apart from the fact that someone had replaced the mains cord with a length of fabric covered iron flex. The speaker and smoothing capacitor are both dated May 1949.

Inside there was some dust, but not a great deal so I vacuumed it clean and set about the checks recommended on this forum and elsewhere, in advance of applying power. The scale lamp had blown and the tuning dial cord was several pieces. Fortunately, the tension spring was still attached to one of the cord fragments.

Those things aside everything else looked good. I checked the mains and output transformers and the resistances were very close to those in the trader sheet. The insulation on the wiring looked in good condition and the heaters on each of the valves were good. Similarly, the speaker resistance was correct and it responded with a satisfying noise when touched with the probes of my Avo 7 (lovingly restored and supplied to me by Phil G4SPZ) set to resistance.

Someone had disconnected the frame aerial and plugged in a length of wire connected to an aerial plug, but I decided to leave that until I could prove the chassis was going to work. The replacement mains flex was quite new, the plug was serviceable and fitted with a 2 amp fuse.

I fitted a new tuning dial cord, which was a bit fiddly but not as bad a restringing my Cossor 523A. Maintaining tension was tricky as I threaded the cord around the pulleys, but a few strategically placed pieces of tape helped a great deal. After about forty-five minutes the dial was operating smoothly.

Based on the advice on this forum we decided to replace C18 and C20 (Trader sheet 924) before going anywhere near the mains. We also re-soldered the mains lead connections as they didn’t look too great, and we wanted to remove the knot someone had tied in the flex! Finally, we replaced the scale bulb.

Once that was done we applied power to the set through a lamp limiter fitted with a 60W bulb (we would have used a lower wattage bulb, but 60W was the lowest we had). The bulb settled to a reassuringly dim red glow just a few seconds after we applied the power, so we let it run for a while.

We were greeted by a loud hum from the speakers, but the set couldn’t receive stations on any band. However, at that stage I wasn’t too concerned as we were on the lamp limiter. Two things that we did notice were that operating the volume control had no effect, and the power switch was permanently on.

As I had previously noticed that the valve base on valve 1 (the frequency changer) didn’t look too great we gave the valve a waggle and the set began to crackle to audible life. After cleaning the base and valve pins, then more waggling, we could tune the set and receive stations on all three bands and at good volume on the wire aerial.

As the volume switch wasn’t doing anything we replaced C16, not surprisingly the original wax capacitor fell apart as we de-soldered it. The new capacitor solved the volume issue, the pot now operated properly and we could adjust the volume. But still the set wouldn’t switch off, I was still only getting a click in the ‘on’ direction.

A very liberal helping of Servisol and a lot of operations resolved the issue in our favour, as I began to get a satisfying ‘off’ click. I found that the valve base on valve 1, the frequency changer was a little loose so I tightened it, but I think it does need replacing. The wave change switch also needed a fair helping of Servisol.

As the set had worked well on the lamp limiter for some time, we decided to give it a go and try it connected directly to the mains. It works on all bands, has good volume and for a set that is approaching 67 years of age, sounds great. I had it tuned to 5 Live listening to the football and later on Absolute Radio, for now it seems to work very well indeed.

I now plan to tackle the case, although to be honest it is in great condition. The cream paint on the escutcheon, which I understand suffers badly in these sets, has only a couple of tiny chips. I am sure the dark Bakelite case will polish easily.

With regards to the electrics I plan to check the valve voltages against the trader sheet, but if anyone wants to suggest other things that I should check please do so. There are other wax capacitors in the set, which would be candidates for replacement please?

Any suggestions and comments are very welcome.

Best regards,

Gary

[Boater Sam]

Melody Makers, I have several of all the models, nice sets, easy to work on and have a mains transformer.
They suffer from having the aerial coils bottom coupled, slightly insensitive.

Do Not try to clean the inside of the scale, all the printing will come off.

You can change caps if you wish but as you have done the important ones and it is working well it is not essential. The waxy decoupler caps from the HT rail are the only others that you need to think about, it may improve the performance and prevent a resistor burn out in the future, but I have never had that problem.

Assuming this is octal valves, you should be able to clean the sockets and pins OK and slightly tighten the sockets with a toothpick, it breaks before you can apply too much force.

If its B8A valves (E40 series) it is more difficult but can be done with care. Its easier than changing a valve socket especially the frequency changer, lots of wires and the wire is looped into the tags and wrapped around. If you have one or two bad valve pin sockets you may be able to pinch unused ones off the rectifier socket.

I cover the mains voltage selector on the transformer, its too easy to accidentally touch it when working on a live set.

If your on/off switch is single pole, ensure it is switching the live. The selector contacts should then be in the neutral anyway.

Should clean up well with a gentle polishing.

[gary_crutchley]

Hi Sam,

Thanks for the advice and information. I haven't attempted to clean the tuning scale, fortunately it isn't particularly dusty. I did clean the front of the glass but didn't go any where near the rear as I know the printing can be fragile.

With regards to the caps, I will see how it performs for a while and measure some voltages, no doubt I will be back for more advice.

This set has the Loctal valves with the metal bases that snap into place in the valve holder.

The on/off switch is a single pole one and is currently switching the neutral, next job is to swap that around. I will cover the tags on the mains transformer, good point. We also plan to earth the chassis.

I have added a photo of the problem valve holder on the 'wanted' thread.

Thanks again,

Gary

[gary_crutchley]

Well, it polished up very well indeed and is working very well now in our kitchen.

It is picking up stations on all bands with plenty of volume.

Please see photograph attached.

Gary

[Brian R Pateman]

Nice job!

That would grace any kitchen.

[gary_crutchley]

Thanks Brian.

Regards,

Gary

[Lloyd 1985]

Hi,

Well done getting the set up and running, and looking great! I have one of these too, I have done nothing to mine, and it does work well! The guy I bought it off had restored it before I got it. I also have a wooden cased version that was given to me by my Grandad many years ago, I remember using it once and wondering what was smelling of candle wax, turned out to be the radio! The mains transformer was sizzling away merrily while the set continued to work, and spitting wax into the bottom of the cabinet. One day I'll have to open it up and do some work on it.

Regards,
Lloyd

[gary_crutchley]

Good story Lloyd, sounds like the mains transformer might be 'slight over'!

Gary

[Boater Sam]

Go on Lloyd, fix it! I'll bet the transformer is OK, they were very robust.
It will be duff caps, especially 'That cap'.

I had a 501AC that had a pyramid of wax in the bottom under the transformer, it is still working but it had cooked the output valve due to cap leakage.

Some of these had 6V6G output valves and with the good sized speaker they have, they sound superb.

[Lloyd 1985]

I will have to soon, I dug it out of the loft of our old house in Daventry (surprised it didn't get left behind, a lot of stuff did!), and now it's sitting on the bookshelf in my parent's new house in Coningsby! I need a new workshop before I can really do any proper work, but I think this should be the first set to be restored in the new workshop. Much to my amazement, the set does still work! When it was spitting wax everywhere, it had been on all day playing 'Classic gold 1359' as it was back then!

I'm not sure what valves are in that set, they were the small ones with the glass pip on the side of the base, that breaks off if your not careful taking the valves out! It did sound quite good before it sizzled. The 494AC that I have sounds good too.

I'll try and remember to get a photo of them side by side this weekend, when I'm back in Lincs.

Regards,
Lloyd

[kalee20]

I have a 500AC, very similar chassis.

The mains transformer died on me very soon after acquiring it (damp storage?) but I rewound this.

Performance is mediocre - tracking is not very good - but the large loudspeaker and generous output valve (7C5, very similar to 6V6) results in good sound quality.

It's an easy chassis to work on, too - easily removed, compact, few trailing leads.

[mark pirate]

Performance is mediocre - tracking is not very good - but the large loudspeaker and generous output valve (7C5, very similar to 6V6) results in good sound quality.

I spent a fair bit of time recapping and fettling mine, but it has never performed
That well, your description sums up the set well!

They do look nice when the Bakelite is polished up though.

Mark

[Phil G4SPZ]

Nice write-up Gary, well done indeed.

[gary_crutchley]

Thanks Phil, much appreciated.