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Old 15th Dec 2018, 4:19 pm   #41
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Default Re: 1938 Murphy A56V television restoration

A number of A56V's must have been sold new after WW2. The one at the museum has 'November 1939' on the ME speaker and it is the original. They must have used up the last of the components and built a few receivers after the close down.

A Murphy dealer with a warehouse in Holborn London offered to store the remaining stocks of television receivers for Murphy Radio. Due to war work they desperately needed the space they were taking up.

During early 1946, in time for the reopening of the service it appears that Murphy dealers were allocated one receiver from the V80 series but by the wording it appears they had to pick it up personally from the Holborn warehouse that had miraculously survived the air raids. [Murphy Service News]

Yes Mike an incredibly ugly sister but neat and tidy for pre war. My 1947 V114 looks very similar. Regards, John.
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Old 15th Dec 2018, 10:11 pm   #42
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Default Re: 1938 Murphy A56V television restoration

Quote:
Originally Posted by mark pirate View Post
I think there is only a handful of V136C's known to exist, there was also different front legs used on the cabinets. The V134C is the same set minus the two valve pre-amp.
This unfortunate V136 is still awaiting attention.

https://www.vintage-radio.net/forum/...d.php?t=145895

DFWB.
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Old 16th Dec 2018, 9:28 am   #43
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Default Re: 1938 Murphy A56V television restoration

Quote:
This unfortunate V136 is still awaiting attention.
Hi David, my set is also patiently awaiting attention.
It was so close to being completed when frame collapse stopped play
It just remained to get the hacked about receiver chassis returned to the original Murphy circuit.

I really should get back to it, although I fear the weird frame output TX/scan coils have gone O/C.

Mark
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Old 16th Dec 2018, 10:47 am   #44
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Default Re: 1938 Murphy A56V television restoration

Yes a very odd receiver David. I think it is Murphy's only TRF television. The height of madness!
Can you imagine 2 X 6P28s to scan a 9" tube then go to all that trouble to design a single valve frame output stage.

Those high impedance scanning coils combined with the oscillator transformer must have been a costly experience.

The A56V and the post war V114 are very reliable once sorted. My V114 has run for over 15 hours without the slightest hitch. All great interest to us but must have been hated in their day. John.
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Old 17th Dec 2018, 7:42 am   #45
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Default Re: 1938 Murphy A56V television restoration

Hi everyone,

I'll start on the restoration at the beginning. That was the power-supply unit. There were two reasons why I started on the power-supply unit first. Firstly, I wanted to know ASAP the status of the mains transformer and the EHT transformer, especially if they needed rewinding. Second, the power-supply unit is self-contained, and so it was easier to tackle than the main chassis, and should hopefully give me a feel for what I might expect later in the main chassis (if you expect to hit problems, its better to first hit them on the power-supply unit, and so you're forewarned when moving to the more complex main chassis).

I first did a comparison of the power-supply unit against the service manual, this is obviously important as often you can't rely on the service manual being always correct. This highlighted the usual post-war 1946 modifications relating to electrolytic replacement. The originals had all been replaced with 1946 eqivalents, except for the Dublier 0.1 mfd EHT capacitor, these are generally known to be reliable and not to need replacement. All in all nothing there was very surprising there.

I then did an internet search to bring up as many photographs of other A56V/A58V power-supply units as possible. This brought up photographs of two other A58V power-supply units. A comparison of those showed the 1946 modifications were identical across the 3 units, including the replacement of a 100 uf capacitor with two 50 uf capacitors with identical mounting. This strongly suggested all modifications were done by Murphy or Murphy dealers.

Photo 1 shows the underside of the power-supply unit, with the two 50uf capacitors mounted on the chassis (wrapped in brown card).

Comparing the modifications against the service manual, brought up one difference. Originally, the set was specified to use two UU4 rectifiers in parallel, with 2 8uf reservoir capacitors in parallel, and two 16uf smoothing capacitors in parallel. In this set this had been changed to two UU5 rectifiers and a consequent doubling of the reservoir and smoothing capacitors (to take account of the greater UU5 load capacity). I have no doubt this was part of the 1946 Murphy modifications as UU4 valves by 1946 were listed as discontinued (UU5 was listed as a replacement).

There was one additional unexplained difference between this unit and the service manual. On the mains transformer the 4V filament winding for valves and the 2V CRT filament winding are taken out to tags on a board. These were reversed in respect to the service manual. There is absolutely no reason for anyone to have changed this, and so it is probably original. This is possibly due to this being an early set (according to the serial number, in the first 100 made). A nasty gotcha if you were relying on the service manual to be correct.

The question that arose here was, do I restore to the original 1938 specification, or restore to the 1946 modification.

Personally this was a "no brainer". I have no information on how the original 1938 power-supply unit looked, and any attempt is likely to be a pastiche, due to lack of information. On other hand the 1946 modification is a valid part of the history of the set, and a restoration to that is historically valid, and in my mind much better than a 1938 pastiche.

Having decided to do that, the first task was to completely strip the chassis and repaint. Photograph two shows the chassis mostly restripped down. Next was restuffing the existing capacitors with modern components. As expected the Dublier 0.1 uf EHT capacitor proved on a megger to be OK, and it was kept as is.

The next task was the mains transformers and the EHT transformers. These were extremely rusty, but on testing they showed the expected results for the various windings, and none showed any shorts to the laminates/core or to other windings. I was extremely surprised by this, and I thought it was too good to be true given their very rusty state. My opinion was they'd short out on first use due to green-spot that wasn't showing up on my multimeter tests.

I obviously sought the advice of Mike Barker, as he is obviously very experienced in transformers. Should I simply send them to him for rewinding now, or wait and see?. His advice was to bake them between 60-80 degrees celsius for a couple of days to drive out any moisture. Presumably then to wait and see what happened. I did just that. Unfortunately my oven doesn't go down to 60-80 degrees. I spent a while wondering how to bake them at that temperature, and then thought about slow cookers. They're designed to bake something at a low temperature for many hours, ideal. I bought a slow cooker, measured the temperature it got up to (60-80 degrees), and then baked them for 8 hours at a time, over a week. The 8 hour limit was because I wanted to keep a constant eye on the baking, and I had discovered the temperature control wasn't perfect by using a thermometer . After 8 hours it crept up higher than 80 degrees.

Having done that, they were still very rusty. I don't like rust or the continuing corrosion that it implies due to penetrating rust and loss of protection (either painting or plating). Besides that the wiring and wiring insulation from the windings etc. was badly corroded and needed attention (by definition if the wiring fron the windings is badly corroded what does it say about the transformers themselves, which is why I personally thought the transformers were destroyed by damp despite what the readings said).

I stripped the mains and EHT transformers down, and removed all the rust from the various metal assemblies and laminates and repainted or treated with lacquer to prevent further corrosion.

Photograph 3 shows some of the rust treated and polished metal assemblies from the mains transformer.

The EHT transformer had some of the worst corrosion. It has a paxolin panel mounted on it which holds the EHT rectifier and the EHT bleeder resistors. All of the bleeder resistors were open circuit, there was a high level of corrosion everywhere, and the paxolin board was badly cracked.

The earthy side of the EHT winding was badly corroded and green. This was fine wire and on the removal of the paxolin board for repair, it disintegrated.

Photograph 4 shows the EHT transformer with the paxolin board and the bleeder resistors. The EHT winding wire is at the bottom right of the lowest bleeder resistor.

Photograph 5 shows the EHT transformer after the removal of the paxolin board. The disintegrated EHT wire is barely visible, in green, on the right hand side.

I have run out of time. To be continued.
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Old 18th Dec 2018, 5:42 am   #46
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Default Re: 1938 Murphy A56V television restoration

PSU restoration Part 2

That corroded EHT winding wire proved to be a major problem. I tried soldering a wire to it, but of course, being corroded the solder wouldn't stick (but it was worth a try). I tried cleaning the wire, and the inevitable happened, it snapped off clean to where it emerged from the transformer

At this point there seemed very little option but to send it to Mike Barker for rewinding. But then something unexpected came to the rescue.

Wax. The EHT transformer windings are heavily impregnated with wax, and there was a layer of wax on top of the transformer. Melting away the wax revealed about 3mm of uncorroded EHT winding wire. I managed to successfully attach a wire to that.

I stripped the EHT transformer down, de-rusted the metal assemblies and repainted. I stripped the EHT circuit (rectifier and bleeders) off the paxolin board, cleaned and glued it (where the hair-line cracks were) to strengthen it. I then rebuilt the EHT circuit with new components., as they were all open-circuit.

Finally I stripped down, de-rusted and repainted the chokes. Then I put it all back together with mostly new wire (the systoflex covering was mostly OK and didn't need replacing).

Photo 1 shows a photo of the unrestored mains transformer, because I didn't have room in the previous post.

Photo 2 shows some of the treated metal assemblies on the EHT transformer.

Photo 3 shows the stripped down, and restored paxolin board,

Photo 4 shows the rebuilt EHT circuit on the paxolin board.

Photo 5 shows the underside of the finished PSU.
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Old 19th Dec 2018, 5:03 am   #47
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Default Re: 1938 Murphy A56V television restoration

A couple of people have asked for the photos taken during the restoration. As I took hundreds, I'm happy to oblige showing the restoration each stage from start to finish. Obviously I can only show a few due to the 5 photograph limit, and so I'll choose what I think are the more interesting ones at each stage. But if you think I'm going too slowly, please mention it,

With the PSU finished I moved onto the main chassis. The next couple of months was spent stripping it down of components that needed restoring. Due to the generally rusted condition of the set, this was a slow process. A lot of the stuff wouldn't budge, and I don't like going to drastic measures unnecessarily, so a lot of soaking was necessary.

What needed to be removed? Obviously the electrolytics and the waxies. None of these on testing showed to be any good.

But, there was most of the top of the chassis, the transformers (audio, frame and line), the deflection coils, the mount (on top of the chassis) on which the CRT sits, the mount (on the bottom of the chassis) which holds the focus coil, and the CRT clamp. The wirewound trimmers needed to be removed because they were open circuit.

These all needed work on them.

Photo 1 shows a view of the bottom of the chassis, when I got the television. I realised I'd not shown a picture of that.

Photo 2 shows the removed "bottom CRT mount". This has a clamp, and it also has three brass knobs on threaded bolts, with springs, these adjust the focus coil (unseen as it on the other side). Both of these were rusted solid, and would subsequently need a lot of soaking to free up (if you're wondering how brass can rust, it obviously doesn't, it was the bolts that were rusted so they wouldn't move).

Photo 3 shows a close view of the frame transformer and deflection coils just before removal. This not only shows their generally rusted state, but, it also shows the state of the wiring. If you look closely at the wiring on the frame transformer, you should notice it is covered in white spots. At first I assumed this was mould, but mould is easy to brush off, and this wasn't. It is hard and won't easily break off. So where did it come from? Breaking the cotton covering and all becomes clear. Beneath the cotton covering was probably a layer of white rubber, this rubber has perished and it has left white dust which pours out on breaking. The white spots is presumably where it has sweated through the cotton in the damp conditions, leaving a dried hard white deposit.

The frame transformer will need to be completely stripped down due to its rusted state (along with the unshown audio output transformer in a similar state).

Photo 4 shows the removed deflection coils. If you look at this previously posted photo (https://www.vintage-radio.net/forum/...0&d=1544678770), you should be able to see the deflection coils are attached to the chassis via two sprung steel strips. Due to the fact the adjustment had rusted solid, at some previous date the sprung steel had been badly bent when the CRT had been inserted (due to being out of adjustment, and immovable). This has resulted in one of the steel strips breaking due to undue pressure.

The deflection coils will need to be stripped down to fix this, and the generally rusted state.

Photo 5 shows the removal of one of the wire-wound trimmers. The screws being rusted and soft, despite soaking, rounded off, requiring them to be drilled out. The photo also shows the generally grimy state of the under-chassis tag boards.
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Old 20th Dec 2018, 6:05 am   #48
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Default Re: 1938 Murphy A56V television restoration

This should be the last lot of photos showing close-ups of the pre-restoration state.

Photo 1 is the other side of the "bottom CRT mount" showing the focus coil. The visible brown pipe contained the EHT lead, evidently for extra insulation against the earthed metal work.

Photo 2 is a close-up of the RF and Frequency Changer stages. In my first post I gave an overview of the set's state when I got it, and mentioned due to corrosion a number of mica capacitors had already fallen off, and some where on their way, just hanging on with corroded legs or just one leg.

If you zoom this photo in, you may be able to see the two wires on the top-left valve socket (V1 the RF amplifier) where two mica capacitors were, but have fallen off (they're immediately above and to the right of the brown/yellow resistor).

The bottom half of the photo shows the Frequency Changer circuit, the coil on top of the rusty bracket is the oscillator coil, and the bracket contains the tuning/trimming mechanism, which moves a brass rod in and out of the oscillator coil. You should also notice there are tags on top of the oscillator coil (there's 8 in total, but you can see about half). A large part of the Frequency Changer circuit is built on top of this coil, around the circumference. This is obviously to reduce signal path length, as this will be operating at 40.75 MHz. The coil and components are also almost immediately over the Frequency Changer valve socket, obviously again to reduce signal path length.

Perhaps due to the presence of the metal bracket, and the tight packing of the components, this circuit has suffered from a fair degree of damp, and corrosion as a result. You should be able to see that the brown mica capacitor leg is corroded, and in fact broke while I was examining the circuit, If you zoom the picture you also may be to see a blue capacitor which is hanging on by one leg only (next to the Green and Orange resistors). There is also a corroded bare wire next to them (compare that wire to the wire on the mica capacitor sitting in the valve socket, that is almost the only mica capacitor that survived unscathed in that circuit). That is not all I found corroded within the circuit, but the ones visible on that photograph.

Photo 3 is a more zoomed out photo showing the top of the chassis and the dismantling at that point. I have included this photo primarily because in the bottom left hand corner, it shows the coil immediately beneath the oscillator coil, which isn't shown in the previous photograph. That is the sound rejection coil in the cathode of the first video IF amplifier. Again Murphy has built up a (less complex) circuit on top of the coil, and it again suffers from the same problems mentioned previously.

You should be able to see a round white mica capacitor, this has been visibly affected by damp (I should point out at this time I was visually inspecting the set for damaged components and removing them for repair or replacement, electrical tests on other non-visually damaged components will come later as needed).

Photo 4 is a photo of that removed component dismantled showing the effects of corrosion.

The last photo shows the repaired white mica capacitor. A modern component has been inserted and the empty shell filled with putty. It also shows one of the brown Dublier mica capacitors in the Frequency Changer circuit, which could be repaired as there was a nub of wire left to solder a new connection. The blue capacitor is shown before repair, but this was successfully repaired by soldering a new leg onto it.
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Last edited by Catkins; 20th Dec 2018 at 6:10 am. Reason: forgot to mention what the brown pipe was for
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Old 21st Dec 2018, 11:35 am   #49
Peter.N.
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Default Re: 1938 Murphy A56V television restoration

Very nostalgic that, body end and spot resistors and components you can sometimes actually repair. You have done an excellent job there.

I wonder how much it would cost to make components like that now.

Peter
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Old 21st Dec 2018, 2:13 pm   #50
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Default Re: 1938 Murphy A56V television restoration

I have been following this thread with interest as over the last few months my project has been to sort out the Wireless Museum's A56V , it has been a bit of a struggle as we have had to remove a few " Gerryfications " but thanks to the very kind donation from David Newman , we now have the correct mains transformer and the power supply circuits put back to what they originally were .
The final problem to fix turned out to be a missing 32uF capacitor across the HT supply to the Line and Frame stages ( c69 and c71) two 16uF's in paralled ( and missing) but please enjoy the Photos and soon you will be able to see it working at Dulwich
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Old 21st Dec 2018, 2:29 pm   #51
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Default Re: 1938 Murphy A56V television restoration

A very good and bright picture!

Peter
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Old 22nd Dec 2018, 12:32 am   #52
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Default Re: 1938 Murphy A56V television restoration

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The final problem to fix turned out to be a missing 32uF capacitor across the HT supply to the Line and Frame stages ( c69 and c71) two 16uF's in paralled ( and missing) but please enjoy the Photos and soon you will be able to see it working at Dulwich
Odd that c69/c71 were missing, as they're very visible! Being bolted to the CRT mount.

In the attached photo, it is the top electrolytic capacitor, these were replaced in the 1946 refurbishment, but the original was a double capacitor too.

I assume the original had been removed, and nothing put back in it's place?

I image the lack of it would have caused hum and generally instability in the timebases.

Phillip
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Old 22nd Dec 2018, 12:37 am   #53
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Default Re: 1938 Murphy A56V television restoration

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A very good and bright picture!
I agree it looks a very bright picture. Is this the original CRM91 tube?
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Old 22nd Dec 2018, 1:30 am   #54
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Default Re: 1938 Murphy A56V television restoration

Quote:
Originally Posted by Peter.N. View Post
Very nostalgic that, body end and spot resistors and components you can sometimes actually repair. You have done an excellent job there.

I wonder how much it would cost to make components like that now.
Thanks for your comment. I try to repair as much as I can in these sets to keep as much originality and look as possible. It is nice that so many of these components can be stripped down and repaired - that is even after 80 years and corrosion they're still repairable.

Today after many years of cost cutting, it is simply not possible to strip components down, even if you try, they usually fall apart. I doubt much of today's electronics will be repairable in 20 years, let alone 80.

Of course in conjunction with the lack of repairability of single components, is the pull out the unit, and put in a new one, style of servicing. You're not even supposed to try and repair single components.

This is not a new phenomenon. I was repairing a 1970s VT100 computer terminal, and there was fault in the power-supply. The "service manual" simply said replace the entire board. No much use, but, it was easy enough to track the fault down to the exact component.

I fully expect, if we ever end up in an end of civilization dystopia, everything made in the last 40 years will end up in the scrapheap, and we'll be getting all the designed to be repairable stuff out of museums. A sad critique on our throwaway culture.
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Old 22nd Dec 2018, 1:50 am   #55
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Default Re: 1938 Murphy A56V television restoration

Quote:
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Odd that c69/c71 were missing, as they're very visible! Being bolted to the CRT mount.

In the attached photo, it is the top electrolytic capacitor, these were replaced in the 1946 refurbishment, but the original was a double capacitor too.
Out of curiosity, did you have the bottom electrolytic? (originally containing C28/C29/C67/C68), or was that missing too?

Last edited by Catkins; 22nd Dec 2018 at 1:52 am. Reason: Add "originally" for clarity
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Old 22nd Dec 2018, 12:34 pm   #56
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Default Re: 1938 Murphy A56V television restoration

Hi Phillip

The museum set has a CRM92
The double cap - C69/71 had been removed many years ago
the power supply had been " modified" many years ago and that cap must have been under the power supply chassis and removed when I removed the "rats nest" and not replaced months ago ( and forgotten about ) I finally spotted it in the circuit and went looking for it and found it missing - it caused a lack of HT on the line and one could only get partial line scan .
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Old 23rd Dec 2018, 1:36 am   #57
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Default Re: 1938 Murphy A56V television restoration

Thanks Peter, it now makes perfect sense.

Phillip
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Old 25th Dec 2018, 4:22 pm   #58
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Default Re: 1938 Murphy A56V television restoration

one old Queen on one old television set
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Old 25th Dec 2018, 4:42 pm   #59
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Default Re: 1938 Murphy A56V television restoration

Looks fantastic. This a very interesting thread as old Murphy's must be rare.
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Old 26th Dec 2018, 11:56 am   #60
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Default Re: 1938 Murphy A56V television restoration

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One old Queen on one old television set
Wrong make and model Peter. It should have been a KB Royal Star. John.
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