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Old 27th Jul 2021, 5:04 am   #1
mister valve
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Default Restoration of a Murphy A40C Console Radio

I recently purchased a Murphy A40C Consul Radio which had largely been unrestored except for the Electrolytic Capacitors, which had been changed. But even those with dates on, were over fifty years old (dated 1967). So those have been changed, along with all the paper capacitors ("waxies"), all of them were electrically leaky (some of them measuring D.C. resistances of just a few hundred ohms). Murphy being Murphy, there was even a "waxie" (C14) hidden away inside the first I.F. transformer can. I have left all the Mica Capacitors untouched, as they rarely give trouble. But I'm told that they can sometimes loose capacitance due to 'silver migration'. A few of the carbon composition resistors had drifted badly, these were also replaced.

Most of the components are mounted on six panels, some crammed full of 'waxies', then there is a "Condenser block" which needed re-stuffing. Fortunately due to Murphy's "cooked spaghetti" style of wiring, there was enough slack and give, to just unscrew each panel from the chassis and lift and tilt them as required. The 'Condenser block' was packed with capacitors & wax, so the tag panel was separated from the internal condensers (capacitors), and the tin box was gently warmed on the gas stove until the wax packing melted and the contents shaken out into the rubbish bin. I then cleaned and repainted the box, then fitted the new capacitors into the tag panel. With todays modern small sized components, this was very easy to do.

For some reason, the trimmer capacitors to the I.F.T's have been 'dismantled' and replaced with postage stamp type trimmers, mounted on tag strips, under the chassis. As the original trimmers inside the cans, have been destroyed, I can't return it back to the original. Apart from that, the only other non-original type parts are a '2D4A' double-diode valve which replaced one of the 'V.914' original valves. But I have acquired a 'V.914' from someone on this site, as the '2D4A' has an open circuit heater. (I have temporarily borrowed a 'DD4' from a Cossor radio in my possession until the V.914 valve arrives).

I have replaced all the perished 'Rubber Grommets', repaired the clutch switch on the back of the main tuning condenser, cleaned all switches with "Servisol", re-strung both tuning drive cords (one was broken, the other was frayed), replaced the mains lead (which was in a dangerous condition).

Now the 'purists' are going to cringe when I say I have fitted a 20mm chassis surface mount fuse holder plus fuse in the H.T. return, this is a safety measure to hopefully protect the mains transformer H.T. windings plus the two UU4 rectifiers against H.T. shorts, or excessive current being drawn under a fault condition. The fuse & holder is hidden behind the rectifier valves, & just in front of the Mains Transformer where I utilised a small hole already in the P.S.U. chassis, which I was able to put a nut and bolt through to hold the fuse holder in place. You wouldn't even notice it, if you didn't know it was there !!

Having thoroughly checked everything, it was time to test the set.... After a few crackles, it burst into life. Considering I am yet to re-align the set it works remarkably well. Even the A.T.C. circuit seems to be working properly. So far, the only disappointing feature is the rather 'thin' Bass response this set has - all the more disappointing when you consider the massive loudspeaker that it has. (I have checked the L.S. cone for condition, & free movement). As I haven't heard another one of these sets working, I can't really compare it. Maybe they didn't have a big 'boomy' Bass response. However there is no shortage of output power from those two "AC/4PEN" output valves in Push-Pull !!

My next task will be to re-align the whole set, to the manufacturers instructions (which are quite involved on this chassis).

Hopefully, I can upload some pictures of the work I've done.
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Last edited by Radio Wrangler; 27th Jul 2021 at 8:43 am. Reason: Spelling in title
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Old 27th Jul 2021, 5:19 am   #2
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Default Re: Restoration of a Murphy A40C Consul Radio

Hopefully the pictures of some of the restoration work I did on the Murphy A40C will now upload !!!!
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Old 27th Jul 2021, 5:50 am   #3
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Default Re: Restoration of a Murphy A40C Consul Radio

Some more pictures of the before and after, under chassis restoration. The fifth picture shows the new capacitors mounted on the tag board, ready to be inserted into the freshly painted 'condenser block' can (shown in the forth picture along).
The first & second pictures show the 'condenser block' can in the unrestored condition.
The third picture shows an unrestored panel still with its original waxed covered 'paper capacitors'.
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Last edited by mister valve; 27th Jul 2021 at 6:03 am.
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Old 27th Jul 2021, 8:09 am   #4
Nickthedentist
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Default Re: Restoration of a Murphy A40C Consul Radio

Nice work, I look forward to seeing a pic of the finished instrument complete with cabinet.

Nothing wrong with a bit of extra fusing. If the mains transformer were to burn out, that would leave things much more un-original!

BTW, this thread implies that the bass response should be good: https://www.vintage-radio.net/forum/...d.php?t=109873 See post 7 etc.
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Old 27th Jul 2021, 1:07 pm   #5
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Default Re: Restoration of a Murphy A40C Console Radio

First picture shows the P.S.U. chassis, the second picture shows the new addition of an H.T. Fuse (with cover), the third picture shows the receiver chassis, the forth picture shows the front of the cabinet, finally the fifth shows the dial lit up and 'Magic Eye' working. I think the magic eye is 90 degrees out, this is due to someone in the past changing the 'Magic Eye' and valve base from an "AC/ME" on a 'British 7 pin' base, to an "ME41" on a 'Mazda Octal' base. Electrically they are identical. If I can get an "AC/ME" at a reasonable price in the future, I may change the base back to the British 7 pin base and fit the valve it should have. In the mean time, I'm not too bothered about the 'wrong' Magic Eye in the set.
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Old 27th Jul 2021, 2:55 pm   #6
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Default Re: Restoration of a Murphy A40C Console Radio

Nice work and a very high quality set !

Andy
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Old 27th Jul 2021, 4:23 pm   #7
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Default Re: Restoration of a Murphy A40C Console Radio

Fantastic job, you're a braver and more competent person than me. My A40 probably needs looking at but the prospect is rather daunting!
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Old 27th Jul 2021, 7:35 pm   #8
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Default Re: Restoration of a Murphy A40C Console Radio

Quote:
Originally Posted by mister valve View Post
As I haven't heard another one of these sets working, I can't really compare it. Maybe they didn't have a big 'boomy' Bass response.
Given the size of the loudspeaker I too was surprised that there wasn't a weightier bass response in the one I repaired many years ago.

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Old 27th Jul 2021, 8:07 pm   #9
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Default Re: Restoration of a Murphy A40C Console Radio

When you first look under the receiver chassis of this set, the total 'birds nest' of wiring you are confronted with, is enough to change your mind about even touching it, let alone restoring the receiver. I remember thinking "how on earth did they ever get these things to work".... Well they did

I started off with the P.S.U. chassis, first checking the Transformer windings were not open circuit, then the two chokes for the same. I then fitted a new reservoir & smoothing capacitors clamped underneath the chassis, but retaining the old 'can' capacitors disconnected, but in their respective positions for aesthetic reasons. I also fitted C81 & C82 which are two 0.01uF caps. that go across the H.T. windings. These were missing ! I used 0.01uF @ 1kV Disc Ceramic, which are ideal for filtering out high voltage spikes, which could cause Anode / cathode flashovers in the rectifiers if they exceed the maximum ratings of the UU4 Valves.

Next I tackled the 'easy' panels first under the main chassis. Panel 6 is the easiest, as it only has two capacitors and two resistors on it. The most difficult one to do was panel 1 and I saved that 'til last. Even the 'Condenser block' wasn't as difficult as I thought it would be.

I found the best way to restore the set was to do a little and often, rather than trying to do all of it in one go.
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Old 30th Jul 2021, 12:28 pm   #10
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Default Re: Restoration of a Murphy A40C Console Radio

Thought I would just mention that those rather 'shaky' black lines drawn around one end of the yellow replacement capacitors, is to denote that it is the "outside foil".

Unfortunately, the manufacturers don't mark them like they used to; so I had to find out using an oscilloscope with its leads across the cap. and holding the body in my fingers to induce 50 c/s mains hum and checking which way round gave the lowest amplitude trace on the 'scope. Which ever the earthy side of the probe was connected - that would be the "outside foil".

This is a good idea to know, especially when there are a lot of capacitors mounted side by side on each panel. It can be the difference between increased hum, or instability, or neither of them.
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Old 30th Jul 2021, 4:20 pm   #11
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Default Re: Restoration of a Murphy A40C Console Radio

Well done ,they are not the easiest of sets to restore ,yours takes me back to when I did mine , fantastic audio and loads of bass , sadly I sold it on ,just another one that I wished I had kept, good tip with the capacitors thanks , Mick.
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Old 31st Jul 2021, 1:54 pm   #12
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Default Re: Restoration of a Murphy A40C Console Radio

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Well done ,they are not the easiest of sets to restore ,yours takes me back to when I did mine , fantastic audio and loads of bass , sadly I sold it on ,just another one that I wished I had kept, good tip with the capacitors thanks , Mick.
Funny you should mention "loads of bass", because mine seems to lack a good bass response. It has loads of treble & middle, but very 'thin' bass response. With a speaker that size, the bass should be rattling the windows and doors, I would have thought

I checked the speaker cone and the movement.... All seems well.
I have wondered if it might be the phase splitting auto transformer or output transformer that is the problem ? Can't think what else it could be ! I did replace the two output valve's cathode decoupling capacitors with 100uF 25V electrolytic's they should be 70uF, but those are not preferred values these days. I also replaced the 'well cooked' cathode bias resistors, with 120 ohm 5W resistors. The original ones were 118 ohm carbon composition which has drifted drastically in value. Even the new 5 watt resistors get warm in use.

Sound quality is very good indeed, except for the rather 'thin' bass response. Having never heard another one, I can't compare the sound.
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