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Murphy A36. Another wreck for restoration.

 
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Murphy A36. Another wreck for restoration.

Post by Till Eulenspiegel » Tue Jun 23, 2015 9:58 am

I'm awaiting delivery of this Murphy A36 double superhet radio. I'm looking forwarding to making a start on this one. As you can see it is in a pretty bad state but I reckon it can be restored back to working condition.

Till Eulenspiegel.
Attachments
A36_1.jpg
A36_2.jpg

 
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Re: Murphy A36. Another wreck for restoration.

Post by Briancuff » Tue Jun 23, 2015 10:10 am

At least it's got a fast access hatch at the side, Till!

 
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Re: Murphy A36. Another wreck for restoration.

Post by Till Eulenspiegel » Tue Jun 23, 2015 10:32 am

From the Radiomuseum: http://www.radiomuseum.org/r/murphy_a36.html

On medium and long waves the IF is only 119Kc/s. On short waves the first IF is 1000Kc/s which should be high enough to keep images at bay, although on other sets made later on the typical IF is 1.6Kc/s. Well away from medium waveband stations.
In 1938 Murphy introduced the A52. This set addresses the low IF problems of the A36. On MW and LW the IF is the now standard 465Kc/s and for short waves the first IF is 3.1Mc/s. Excellent performance on short waves guaranteed.
http://www.radiomuseum.org/r/murphy_a52_a_52.html

Till Eulenspiegel.

 
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Re: Murphy A36. Another wreck for restoration.

Post by Cathovisor » Tue Jun 23, 2015 11:16 am

The manner in which the A36 and A52 work are rather different.

The A36 and the A40C only use a 'nominal' 1MHz 1st IF: the short-wave converter is a wideband device that merely spreads the chosen short wave band across the medium waveband via a bandpass filter. There is precious little selectivity offered by it, unlike that in the A52. Tuning is effected by using the normal medium wave tuner, the 0 - 9 markings on the alphabetical drum corresponding to 100KHz divisions so the only real selectivity comes from the MW/LW IF which, at 119KHz, isn't that great. The point of the A36/A40C system was to make short wave tuning easier. This method also means that on the A40C, the ATC is operational on short waves as well.

http://www.murphy-radio.co.uk/diagrams/A36.jpg

 
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Re: Murphy A36. Another wreck for restoration.

Post by Cathovisor » Wed Jun 24, 2015 3:12 pm

Another trap for the unwary in the A36: the audio is reflexed through the SW RF amp.

 
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Re: Murphy A36. Another wreck for restoration.

Post by Till Eulenspiegel » Wed Jun 24, 2015 3:33 pm

That's right but only on Long and Medium wavebands. The first task is to stabilise the cabinet. It goes without saying a new side panel will have to be made.
As for the electronics? Any ones guess what they'll be like.

Till Eulenspiegel.

 
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Re: Murphy A36. Another wreck for restoration.

Post by crackle » Wed Jun 24, 2015 8:05 pm

That looks like a real challenge, but it should be a nice radio when its done.
Mike

 
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Re: Murphy A36. Another wreck for restoration.

Post by Till Eulenspiegel » Wed Jun 24, 2015 8:39 pm

Hi Mike,
I'm informed from good authority that the A36 can indeed give a good account of itself.
This must be one of the first post Frank Murphy era models. Many will recall the story. When Mr Murphy was away on a fact finding tour of the United States members of the companies' board of directors relieved him of the directorship of his own company.

Till Eulenspiegel.

 
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Re: Murphy A36. Another wreck for restoration.

Post by Cathovisor » Wed Jun 24, 2015 8:56 pm

Cathovisor wrote:Another trap for the unwary in the A36: the audio is reflexed through the SW RF amp.
Till Eulenspiegel wrote:That's right but only on Long and Medium wavebands.
Not true - the audio reflexing is operative on all wavebands.

 
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Re: Murphy A36. Another wreck for restoration.

Post by Till Eulenspiegel » Wed Jun 24, 2015 9:18 pm

I stand corrected. V5 (AC/VP2) functions as the RF amplifier on short waves and is the AF amplifier on all wavebands. So it follows the only non functioning valve on MW and LW is V6 (AC/TH1) which is the SW frequency changer only.
More info and photos here: http://www.classicwireless.co.uk/Murphy_A36.htm

Till Eulenspiegel.

 
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Re: Murphy A36. Another wreck for restoration.

Post by Till Eulenspiegel » Thu Jun 25, 2015 11:44 am

News Flash! The set was delivered this morning. Sure enough it is a wreck but the good news is everything is there, including those cabinet side panels.
This one will get my my engineering mojo going.

Till Eulenspiegel.
Attachments
A36_0165.jpg

 
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Re: Murphy A36. Another wreck for restoration.

Post by Till Eulenspiegel » Thu Jun 25, 2015 6:05 pm

The restoration may not be so difficult after all. At least the knobs came off fairly easy after a squirt of penetrating oil.

The first task will be the easy bit, reassemble the cabinet.

Till Eulenspiegel.
Attachments
A36_0166.jpg
A36_0166.jpg (99.85 KiB) Viewed 3620 times
A36_0167.jpg
A36_0167.jpg (113.78 KiB) Viewed 3620 times

 
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Re: Murphy A36. Another wreck for restoration.

Post by crackle » Thu Jun 25, 2015 7:47 pm

Do I spy a sheet of spare veneer on top of the cabinet. :)
Its good it has a full set of matching knobs. I always find the speaker grill cloth is the most challenging, if it is torn badly it needs replacing but other wise best left alone.

Mike

 
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Re: Murphy A36. Another wreck for restoration.

Post by Cathovisor » Thu Jun 25, 2015 7:58 pm

Till Eulenspiegel wrote:This must be one of the first post Frank Murphy era models. Many will recall the story. When Mr Murphy was away on a fact finding tour of the United States members of the companies' board of directors relieved him of the directorship of his own company.

Frank Murphy returned from his Stateside fact-finding mission early in November 1936 and he resigned from the company in January 1937.

The A36 was indeed released after his departure, but he would most definitely have been in charge during its development.

 
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Re: Murphy A36. Another wreck for restoration.

Post by Till Eulenspiegel » Fri Jun 26, 2015 12:46 pm

I've made some real progress today. Usual tests around the base of the AC2/PEN output valve revealed positive volts on the control grid.
Changed the coupling capacitor and that action should solve a lot of problems because the detector diode cathode is referenced to the cathode of the output valve. There is a tricky noise suppression circuit in this set. Fortunately it can be switched out.
The volume control is faulty so for the time being it has been bypassed. I noticed that the heater of the AC/VP2 IF amplifier was not lit up.
A near equivalent to this valve is the Mullard VP4B so one has been plugged in and now already MW and LW stations are coming in.
Stability is bad, the metalising of the AC/TP frequency changer is not making good contact so something will have to be done about that.
No results yet on short waves. No anode volts on the hexode section of the AC/TH1 SW frequency changer. OK on the screen grid and triode section anode.

Till Eulenspiegel.

 
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Re: Murphy A36. Another wreck for restoration.

Post by Till Eulenspiegel » Wed Jul 01, 2015 3:01 pm

The cabinet has been reassembled. That damage to the left side of the front panel is made good, you can't see the joins. The left side panel has been re-veneered and the old veneer used to repair other areas of the cabinet, notably around the edges.
Before any serious work is to done on the chassis, I'll have to find the full service manual.

Till Eulenspiegel.
Attachments
A36_0177.jpg
A36_0178.jpg

 
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Re: Murphy A36. Another wreck for restoration.

Post by crackle » Wed Jul 01, 2015 3:38 pm

That is very good.
What glue do you use to fix the veneer, I have bought some walnut veneer to redo the sides of a GEC radio. I will be gluing it onto Bakelite where the original printed wood effect has come off.
Mike

 
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Re: Murphy A36. Another wreck for restoration.

Post by turretslug » Wed Jul 01, 2015 4:13 pm

Great stuff, Till, I look forward to this set looking and working as good, or better, than new.

 
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Re: Murphy A36. Another wreck for restoration.

Post by Till Eulenspiegel » Wed Jul 01, 2015 5:00 pm

I use PVA glue and an electric iron to lay the veneers on. That damaged left front panel was repaired by applying layers of veneers until the surface is level.

Till Eulenspiegel.


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