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Old 6th May 2019, 10:57 pm   #1
vintage_8bit
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Default Murphy A4

Just after any comments before I start restoration. Please see attached images. Serial No 27350.

The output valve base has been changed to enable an APP4A 7pin to be fitted. The output transformer has an o/c primary so I will be checking the wiring here, although judging by the case its been in the damp. I hope I can find a suitable, in keeping replacement with a 700 ohms primary.

Its been "got at" in other places but nothing serious that I can see.

I have checked for continuity on the speaker coils, IF cans, mains transformers & chokes, all appear ok.

Incidentally, how do the cans come off the coils. Looks like they are just a tight fit? (Tried again, Just removed the 3 largest but not from the IF's)


The oldest radio I have worked on is 1946 so this will be a little different.
I will of course be going through the usual capacitors & I like to re-stuff any electrolytics. The capacitor box will be interesting, I've not had one of those apart yet.

So just after any advice on any problems i'm likly to encounter.

Colin
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Old 7th May 2019, 8:51 am   #2
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Default Re: Murphy A4

The cans on mine just pull off,these are a pretty rare set and mine awaits sympathetic restoration as soon as time permits me.

I notice that the metal Sprauge caps look non original,mine has rectifier diode in as no doubt the valve that is still there is low emission.
Thankfully I have the correct valve to fit.
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Old 7th May 2019, 10:18 am   #3
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Default Re: Murphy A4

At least it's all there and doesn't look like a 'rust bucket' ...... but the cabinet will require some careful and sensitive treatment. Keep us up-to-speed ......
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Old 7th May 2019, 10:42 am   #4
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Default Re: Murphy A4

An interesting set. If you get stuck for the transformer a rewind is possible. I'm not sure of the turns ratio you need, original valve was an AC/Pen I believe and I don't know the required anode impedance of that.
The "capacitor" box contains most of the sets components! It got lots of resistors in too. Very complicated.
Have you got the Broadcaster sheet for this set? it is available from the service data top right.
All is explained therein.

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Old 7th May 2019, 1:19 pm   #5
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Default Re: Murphy A4

Thanks for you replies.

I can apply a bit more effort to the IF cans, now I know they just pull off.

Yes the cabinet, although solid and free from woodworm will need some careful work due to the veneer lifting & missing in places.

Ill check out the rest of the set probably before I deal with the O/P transformer. I have no idea what a rewind would cost, but I’m sure the set would be worth it when all other problems are fixed.

I do have a service sheet for the set thank you. I also got a DVD full, when I joined at Harpenden earlier this year.

Another problem I can see will be the wave change switch, you may be able to see that the 3rd contact from the left has had a repair, which seems to work but it doesn’t look pretty.

I will keep you informed…..
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Old 7th May 2019, 1:44 pm   #6
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Default Re: Murphy A4

Quote:
I'll check out the rest of the set probably before I deal with the O/P transformer. I have no idea what a rewind would cost, but I’m sure the set would be worth it when all other problems are fixed.
The person to contact is aptly named forum member 'Murphy Mad' - Mike Barker, former long serving BVWS Chairman who is an expert on Murphy sets. Mike professionally rewinds coils and transformers for all types of radio and TV sets and I'm sure he'll be happy to advise and give you a quote.

Every success with the restoration. It's certainly a set worthy of full restoration rather than 'doing it up, mending it, or 'getting it going'.

Frank Murphy's advertising slogan back in the day was 'A First Class Job' - not a bad maxim to follow!
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Old 7th May 2019, 9:11 pm   #7
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Default Re: Murphy A4

Thanks for the contact David. I have sent a PM.

With my previous restorations I have tried to keep things as original looking as possible, within my resources. I expect this radio to be more of a challenge but that's where the satisfaction comes from when finished. Colin
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Old 24th May 2019, 10:31 pm   #8
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Default Re: Murphy A4

Update. I am now dismantling the capacitor/resistor block. See image below. Should I remove the 2nd paxolin board after removing the resistors next, or should the whole assembly be heated up to remove as one. I have already tried heating the unit up past the melting point of the pitch. The 2nd paxolin board and terminals rock but won't come out. I'm not prepared to use any force as trying to preserve paxolin and terminals. Any comments gratefully received. Colin.
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Old 24th May 2019, 11:34 pm   #9
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Default Re: Murphy A4

Hi Colin,

You do not need to remove the resistors to get the second paxolin panel out.

You need to heat the whole box up in an oven with the cap block in a tray to catch the mixture of pitch and wax that will seep out.

Put it in for about 45 mins at about 120 to 150 degrees C

The whole thing will then be sitting in a pool of the guts and you should be able to screw the block down to a bit of wood or the bench and pull the guts out with a couple of pairs of pliers by pulling on the solder tabs. They are mounted on a backing board so don't worry about using a bit of force to get it shifted.

I see from your picture that the four small bend over tabs are already straightened.

Give it slow heat and plenty of time.

Don't worry about the resistors. they will already be at least 50% high and should be replaced anyway.


Mike...
The A4 is a lovely set and works really well for what it is.
Mike...
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Old 25th May 2019, 8:58 am   #10
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Thank you for the advice Mike. Hopefully try that today. I will change all the resistors.
If anyone has a good photo of an original looking chassis underside I would be very interested to see it.
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Old 28th May 2019, 7:52 pm   #11
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Default Re: Murphy A4

Update.
That was messy! The paxolin was still difficult to remove, it was catching on solder blobbed on to the case when built, to prevent the lower board from lifting. All cleaned and ready to start re-build now though, see attached.

In the second photo you can where wires have been joined by parting insulation and using a wrap round / hook joint. Is this original, I suspect it is?
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Old 28th May 2019, 8:02 pm   #12
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Default Re: Murphy A4

When I can get mine on the busy bench I will get you a photo. I have all this hassle to look forward to!
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Old 6th Jul 2019, 8:57 pm   #13
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Default Re: Murphy A4

Hi again. Just an update. I have now rebuilt the capacitor / resister box. See photo.

I had a missing terminal on the large square tag board meant to be holding tone control C16 (Trader 544). Two sprague caps had been fitted instead, as noted by HamishBoxer from earlier photo in thread. I have now made up a terminal. See photo.

I have sent off the output transformer for rewind.

My next task is making a better repair of the wave change switch, any ideas here welcomed. See photo. Looks like just brass strip, hardened? to get some spring.
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Old 3rd Aug 2019, 9:51 pm   #14
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So I have now fitted my newly re-wound output transformer, thank you Mike. I have fitted the proper 5 pin valve base for V4, AC-PEN. So the output stage looks as it should, although I had to use a modern cap for C16 (Trader) origional was missing so unable to re-stuff.

My question today concerns electrlytic C18 (Trader). The one fitted looked original to me, its certainly been there a long time. Its a dual 16uF (See photo) that has been paraled up. Trader and Broadcaster say 8uF so I'm assuming this is wrong?
I intend to re-stuff both electrolytics so just wondering what value I should use. I would't want to stress the rectifier. Colin

P.S. I noticed on my set R10,11 & 12 (Trader) are wired correctly but positions swapped to trader and broadcaster sheets.
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Old 3rd Aug 2019, 10:58 pm   #15
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Default Re: Murphy A4

The original was an 8uF wet electrolytic that probably died years ago. I would be inclined to go for the original design value (although not for sake of the rectifier as that is 2 chokes away) as it is possible a larger value might make the hum worse due to the hum bucking design features.
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Old 4th Aug 2019, 9:19 am   #16
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Default Re: Murphy A4

The material for the switch blade is likely phosphor-bronze shim. The contact point looks to be rivetted in but could be carefully soldered to the new blade.

The bodge is interesting!
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Old 4th Aug 2019, 7:33 pm   #17
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Default Re: Murphy A4

Looking at your posts has motivated me to get my A4 out of storage and have another go at it. I re-stuffed the box of condensers and resistors many years ago and, as I remember, it was working reasonably well but I gave up trying to get the volume control to work as it should. A re-visit may provide fresh inspiration now as I am over the frustration.
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Old 4th Aug 2019, 11:00 pm   #18
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Default Re: Murphy A4

Thanks for your replies.

PJL. I will stick to 8uFf then, insides already removed to re-stuff, see photo.

I may have to seek out some phosphor-bronze shim, the contact though is not original and a bit too big. The wave change is next on the list after sorting the two remaining electrolytics.

Geoff. Good luck with the volume control problem. I wasn't so keen at first when I saw the resistor/condenser box. That design does tidy up the chassis though. I like the idea, now the work is done.

Colin
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Old 5th Aug 2019, 10:52 am   #19
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Default Re: Murphy A4

I did a Murphy A46 a few years ago and found that the low value padder capacitors on the LW oscillator coil were bad. They were of a type that looked as if they had been dipped in cement during manufacture. If you have problems with reception when you try your set it maybe worth checking to see whether the same type were fitted.
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Old 6th Aug 2019, 11:05 pm   #20
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Thanks for the tip Paul. Just had a quick look. I couldn't see any caps of that type.
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