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Old 13th Nov 2017, 1:47 pm   #1
Sparky T
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Default Cossor 464 AC - Some newbie questions.

Hi, my wife presented me with my first project last Friday, the above mentioned Cossor 464 AC.

She spotted it at an auction and got it for £8 after it failed to sell.

The case has several bad cracks and had an internal patch made from a small sheet of perspex. That, along with the car body filler that was holding it in, has now been removed.

The mains wiring to the chassis in not original and will be changing it, so first question:

I would prefer to use three core flex with the chassis earthed, is this sensible or stupid?

Next question:

Prior to replacing all the waxies (I've been reading sticky threads) I'd like to check a) heater and b) HT supplies.

Can I do this by removing a) the rectifier and b) replacing the rectifier and removing all (4) other valves?

There will, I'm sure, be many more questions to follow.

Thanks, Andy.
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Old 13th Nov 2017, 2:08 pm   #2
Station X
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Default Re: Cossor 464 AC - Some newbie questions.

Hello and welcome to the forums.

Fitting a three core mains flex is a sensible thing to do.

You can check the LT (heater) supplies with all valves out. Measure at the valve holders. Voltage will be AC.
You can check the HT with just the rectifier valve fitted. Measure across C32, C33 and C34 (Manufacturer's Service Sheet). Voltage will be DC.

I strongly suggest you only replace one waxie at a time, starting with C30, the audio coupling capacitor.
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Old 13th Nov 2017, 3:45 pm   #3
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Default Re: Cossor 464 AC - Some newbie questions.

Only replace the tubular waxed paper capacitors - one - at - a - time Please!

C30 must go, its the coupling before the audio output valve. Leakage here can wreck the output transformer, output valve and even the mains transformer and rectifier.
The flat silver mica ones seldom fail and replacing them upsets the alignment due to tolerances.

Say NO to CCC!

Don't run it too long with just the rectifier valve in, the HT will be much higher than normal and some of the capacitors may not like it.

Last edited by Boater Sam; 13th Nov 2017 at 3:46 pm. Reason: Crossed with Graham, altered.
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Old 13th Nov 2017, 4:44 pm   #4
Radio Tech
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Default Re: Cossor 464 AC - Some newbie questions.

Hi Andy

Welcome to our wonderful forum, here you will find lots of help, expertise and good friends, don't be afraid to ask, and yes, I can only reiterate about replacing the tubular wax looking capacitors, these are notorious for leaking electrically, and also I would suggest replacement of the main smoothing electrolytic capacitor, these very often will show signs of leaking both electrically and physically. When you work through the circuit diagram, highlight each component you replace, that way you will not forget where you got to. Good luck.

Best wishes

Ken
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Old 13th Nov 2017, 6:39 pm   #5
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Default Re: Cossor 464 AC - Some newbie questions.

I hope you enjoy working on the wireless set.

The 6.5v dial lamp, assuming you have a good lamp in the set, will also give you an indication that you have heater volts.

Replace the wax coated capacitors one at a time, start with C30.
I notice that on the RadioMuseum sites circuit this coupling capacitor is marked C30 but on trader sheet 775 (Cossor 464) the same capacitor is marked C22.

Try the set after you have changed each capacitor, that way you make sure you have likely got it right. When you change the decoupling capacitors you may also notice an improvement in the sets performance as you progress one by one.

Wavechange switching and the volume control will probably need cleaning.

If you have a mobile telephone with a camera it is useful to take a few photos of the chassis wiring and components, then if you do get something wrong you can look up how it was before.

John
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Old 13th Nov 2017, 6:52 pm   #6
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Default Re: Cossor 464 AC - Some newbie questions.

The 464 is a heavy little beast

Unusual to have a damaged case its pretty thick Bakelite.

Issues that makes these tricky to restore satisfactorily are.

Tuning scale often very flaky and there are several versions some of which are worse than others.
Knobs the originals are often lost or broken.
Tuning window there should be a plastic/celluloid/perspex moulded window over the tuning scale but its virtually always shrunk or missing.
Tatty looking backs although they are rarely completely missing.

If you have original knobs and a good tuning scale that's a pretty good start

Restored these give a pretty good account of themselves

Cheers

Mike T
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Old 13th Nov 2017, 7:41 pm   #7
kalee20
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Default Re: Cossor 464 AC - Some newbie questions.

Definitely as Station X and Boater Sam say.

Regarding the main smoothing electrolytic, it may fail, as Radio Tech says, but if it looks OK with no cracked rubber seal it probably is OK. Really, if it has not been used for some years, to be sure, you should put low voltage across it, and gradually wind it up. But that may be difficult, so connect your voltmeter, put the rectifier valve in, cross your fingers, and switch on. After the rectifier has warmed up, the voltage should start to rise. When it hits 100V, switch off, allow it to fall (I'm sure this radio has a chain of resistors which will discharge the capacitor). Do this a dozen times over a period of an hour (to allow any heat to dissipate), then allow it to rise to 200V, repeat a dozen times, then finally let it rise to 250V. if it hits that without problems, you'll probably be OK. When you get to power-up properly, with other valves in, just keep an eye on the temperature for the first hour or so.

Looking forward to progress!
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Old 13th Nov 2017, 10:40 pm   #8
Ed_Dinning
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Default Re: Cossor 464 AC - Some newbie questions.

Hi Andy, make a lamp limiter and that will wake up the electrolytics a little more gently.
You can PM me if you are having problems.

Ed
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Old 14th Nov 2017, 2:13 pm   #9
Sparky T
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Default Re: Cossor 464 AC - Some newbie questions.

OK, first update:

Heater circuit is fine, as is the scale lamp.

I didn't read the post about the lamp limiter until after I'd tried the HT. Fortunately there don't appear to be any problems in that area either. No bangs, pops or funny smells.

I tried it with the RF valves installed and all glowed reassuringly. I was a bit surprised as they appear to be the original Cossor items.

The tuning scale is in pretty good nick after a gently clean with a damp cotton bud (several actually). If the attachments showing the case have worked I'll post a scan of the scale later.

You should be able to see the damage and the quality of the previous repair and if you look closely you can see the insulating tape 'protecting' a join in the neutral wire.

I'm off now to source some capacitors.

Thanks for all the advice so far.

Andy
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Old 14th Nov 2017, 10:51 pm   #10
Sparky T
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Default Re: Cossor 464 AC - Some newbie questions.

Here's a scan of the Tuning Scale:
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Old 15th Nov 2017, 1:10 pm   #11
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Default Re: Cossor 464 AC - Some newbie questions.

Quote:
Originally Posted by Sparky T View Post
I tried it with the RF valves installed and all glowed reassuringly. I was a bit surprised as they appear to be the original Cossor items.
Andy
Other than mechanical damage, heater failure (obvious except on small battery valves) and cathode wearout (which takes a loooooong time on a lightly stressed small signal valve) there's little to go wrong with valves. They are vacuum packed after all.

Many 80 year old valves are still perfectly good for a year or many yet.

It's the small parts like resistors and capacitors (condensers) which degrade both with use and time that cause most non obvious problems.
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Old 15th Nov 2017, 1:34 pm   #12
Boater Sam
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Default Re: Cossor 464 AC - Some newbie questions.

That cabinet will repair but will take a lot of work. If you can get all that 'orrible filler off, superglue will make a near invisible repair.
If you need to fill any areas, grind some bakelite off the inside lugs where it doesn't show and mix with superglue - quickly!
Be careful with the knobs, they are not the best and break easily.
The aerial coil is not as robust as it looks, the wires down the inside can get stretched and broken if the solder tags get twisted or overheated, difficult to work out where they go to and from.
Insulate the tags on the top of the mains transformer whilst you are working on the chassis, its too easy to touch them.

Last edited by Boater Sam; 15th Nov 2017 at 1:36 pm. Reason: spellings
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