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Old 13th Sep 2019, 12:43 pm   #1
Superscope
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Default Cossor Melody Master 523.A

I have been putting this repair off, for several Years now, but now I really need to grab the Bull by the Horns and try to actually get this Set Working!

This was my Grandfathers Radio and as far as I know, he had it from New.
I remember it from decades back.

I did at least get round to restoring the Cabinet a while back, where a large parts of the Plywood
& Veneer were starting to separate. It is on show in the Lounge, but it would be better working!

So can anybody tell me anything about this Model?
It has FM which was a surprise, and I guess it Dates from around 1954.

Where is the best place to start?
I am not overly familiar with Valve Equipment.

Last time it was tried, many years ago, it did not power up, but it was used up until the 1990's.

Any help or advice gratefully received.

Ian
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Old 13th Sep 2019, 12:55 pm   #2
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Default Re: Cossor Melody Master 523.A

I would start by getting the service information if you don't already have it.

Get your self a cheap multimeter

Then I would go here and fill you boots!

https://www.vintage-radio.com/repair...ion/index.html

Paul has done some excellent guides.

This is an AC only model so a pretty good set to start on

The centre knobs are not original.

The originals break very easily so are often missing.

And welcome to the forum

Cheers

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Old 13th Sep 2019, 6:38 pm   #3
Malcolm G6ANZ
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Default Re: Cossor Melody Master 523.A

The chassis looks to be the same as the 524 which has a Bakelite case. I did a restore on mine recently. All I did was to replace the essential caps and any out of tolerance resistors. The main problem was the lack of sensitivity on FM, this was resolved by a new ECC85 in the VHF front end.
The inner knobs were missing so I managed to get a pair of ordinary ones to fit, not the correct style but they work and don't look out of place.
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Old 14th Sep 2019, 7:04 pm   #4
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Default Re: Cossor Melody Master 523.A

Hello,

I have restored a 523A and a couple of 524 recently.

They're great sets, very easy indeed to work on, sound great, and work well in a no-nonsense kind of way. An excellent radio for day-to-day listening, which is exactly what one of mine gets used for.

I have some pics on my work PC which I'll try to post on Monday. Let me know if I forget.

Nick.
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Old 14th Sep 2019, 7:15 pm   #5
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Default Re: Cossor Melody Master 523.A

Found a few pics on this PC of one of the 524s. Almost the same as your 523A with a few minor differences (apart from the Bakelite cabinet).

Firstly, I fitted a 3-core mains lead, a rubbert grommet to protect it where it passes thru the chassis, and a cord grip, as well as a 1A fuse in the mains plug. I also fitted a thermal fuse to the mains transformer, in place of the voltage selector, under its top shroud...
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Old 14th Sep 2019, 7:31 pm   #6
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Default Re: Cossor Melody Master 523.A

Then I replaced a handful of waxed paper caps + some smaller electrolytics including the one in the discriminator (apologies to Techman!). The big dual can re-formed perfectly so was left in place, as were the sub-1nF caps, of course.
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Old 14th Sep 2019, 7:32 pm   #7
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Default Re: Cossor Melody Master 523.A

Continued...
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Old 14th Sep 2019, 7:38 pm   #8
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Default Re: Cossor Melody Master 523.A

The Plessey(?) speaker in one of mine had a rubbing voicecoil which did not respond to the usual tricks. I fitted a 6" round LS on a MDF sub-baffle in its place.

I also lubricated the mechanics (including the cam follower) of the wavechange mechanism with a few drops of light oil, if only to take some of the stress off the frail knobs.

The contacts of the wavechange switches were cleaned by applying a drop of Servisol Super 10 to each contact with a small paintbrush, then working the switch back and forth a few times.

The Baklite cabinets were treated with Polishing Paste No. 5, and the wooden cabinet with foaming cleanser then Rustins Scratch Cover.

Results are excellent. Good sensitivity and sound quality, heaps of volume, no tuning drift, and so on.

The knobs are a weak point. I have more radios than I have complete sets of knobs for, by quite some margin.

I also had problems with one of the mains transformers being prone to buzzing lams.

Nick.
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Old 15th Sep 2019, 10:31 am   #9
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Default Re: Cossor Melody Master 523.A

Cobaltblue,

Thanks for the information.

I have the Service Information already.

Multimeter? Time to break out the AVO 8's. Time to give them an outing!

The Centre Knobs not being Original was quite a surprise!
I had assumed these were original, but on closer inspection, I noticed the Wave Change Knob only has M and L engraved on it! So not likely to have come out the Factory like that.

These must have been changed Decades ago, probably as far back as the 70's or 80's. I know my Father didn't change anything, and he inherited the set in 1989.


The Link was excellent, that was just the information I was looking for.



Ian
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Old 15th Sep 2019, 10:48 am   #10
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Default Re: Cossor Melody Master 523.A

Hi Ian

Yes the knobs fitted look like those from a pre-war Philco.

The knobs should look like these on the Radiomuseum site.

https://www.radiomuseum.org/r/cossor_523.html

As Nick says far more sets that knobs!

I think we can all agree a very nice Restro by Nick.

The earliest version of this style knob were solid and reasonably robust so the bean counters got involved and made the knobs hollow and a different material, the wave change gets still ( very common on this series of chassis) and the wave change knob splits.

Both get changed to maintain symmetry

Apologies if my original post seemed a bit condescending it was done in a hurry on my mobile and I faied to spot you were an established member

Cheers

Mike T
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Old 15th Sep 2019, 10:53 am   #11
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Default Re: Cossor Melody Master 523.A

Thanks for the Photo's Nick,

I have started on the old Girl.

Read through the Link Cobaltblue posted.
Most of it is common Sense, but sometimes, it still needs to be written in front of you!
A lot of useful tips.

First job, after getting the Chassis out, was a gentle but thorough clean from all the Dust
Dirt and Grime.
Took the Valves out one at a time, checked them and cleaned the Pins.

No Power applied yet, but first Fault found. Power Switch O/C on one Pole.
Maybe that is why it ended up in the Loft?
That's been fixed now.

Valves checked (for correctness, not functionality at this stage).
65ME Present and correct
6AQ8 Present and correct
6BY7 Present and correct
6BQ5 replaced with EL84 which I believe is the correct equivalent.
6AK8 replaced with EABC 80 which I believe is the correct equivalent.
6AJ8 replaced with ECH 81 which I believe is the correct equivalent.

Whilst I had the Power Switch out, I though I would test that little Hunts Capacitor
soldered on it. I think this is supposed to be 10nF.
Measured this at 16nF which is quite a way off.

I guess I'm going to find most of them out by some margin by now.


Ian
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Old 15th Sep 2019, 11:10 am   #12
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Default Re: Cossor Melody Master 523.A

Ian,

Don't forget that the capacitors in (approx) the 1nF to 1uF range will by now be electrically leaky at their working voltage, even if they test roughly OK on a low-voltage capacitance meter.

The fact that you read 16nF suggests that the cap is leaking (i.e. allowing a tiny DC current to flow) and thus fooling your capacitance meter, not that it's miraculously increased its capacitance over the years

This is why I (and a lot of other people here) would automatically change all of them when restoring a 1950s radio, as it will no doubt improve performance and reliability considerably. The brown/black Hunts ones are notorious, but these sets contain many other suspects too. All but a couple are easy to get at.

Unless you're very experienced, the golden rule is to change just one capacitor at a time, then try the radio to make sure it works at least as well as it did before. That way, if you make an error, it will be easy to spot and correct it.

You may well not wish to make the safety modifications which I did; I have young children at home so like to err on the side of caution. But I would urge you to make sure it's powered from an RCD-protected mains socket (or use an adaptor like those sold for garden machinery), and make sure there's a 3A fuse (certainly not 13A) in the plug.

Good luck with it,

Nick.

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Old 17th Sep 2019, 1:11 pm   #13
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Default Re: Cossor Melody Master 523.A

From memory there is a wax decoupling capacitor within the FM front end box which goes leaky and is easily missed.

If they have survived, the later hollow knobs can be greatly strengthened by cleaning out the hollow carefully then filling it with the slow setting Araldite. I have done this on a knob which was very cracked and weak and it has lasted for several years in regular use.

As others have said these are great sets with good sound and no tuning drift.
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