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Old 15th Sep 2021, 3:40 pm   #1
EF80TVVALVE
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Default 1938 Murphy A56V

Hi all

It's about time I made a thread on this set which I acquired some months ago. As of yet I've done nothing with it and I'm not too sure how far I will go in terms of restoration, the cabinet is certainly on the list as the varnish is in poor condition along with the top where some veneer is lifting.

The rear card cover is missing, something I hope to make a replica of once I have time but the set looks very nice and mostly untouched bar a couple of missing AC5PEN valves. The screen mask isn't the original, I do have it but it has been in the bottom of the set for many years and has deformed and hardened. I may try the softening method using oil of wintergreen but I think really it is too far gone. The CRT is the original CRM91.

There are a few period repairs but it is very much original which is making me consider leaving it as is. Although leaving it unrestored makes it nothing more than an ornament I do feel torn making repairs on such an early set. If I were to restore then it will have to be a very sympathetic restoration, restuffing caps etc.
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Old 15th Sep 2021, 3:55 pm   #2
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Default Re: 1938 Murphy A56V

Hi EF80TVVALVE,
That's a lovely set, one of my favourites.

Your set is in great condition. So often pre-war sets have rusty chassis. The important fact is that the large safety glass is intact as is the original speaker cloth. The veneer repair should be fairly simple (not my area of expertise though). I think this missing knob can be found on a Murphy radio of the period.
I would always want to restore a set to working order, just because that is the way I roll I'm definitely for re-stuffing as well as fitting vintage resistors where required. Anyway it's up to you of course and you can leave that decision for later and just enjoy it as it is for now.
BTW, have you ever seen the one at the museum working? It produces very good picture, as good as any early post-war set.

Cheers
Andy
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Old 15th Sep 2021, 3:59 pm   #3
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Default Re: 1938 Murphy A56V

I would echo Andy's thoughts too.

Peter.
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Old 15th Sep 2021, 4:37 pm   #4
EF80TVVALVE
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Default Re: 1938 Murphy A56V

Thanks Andy for your advice and Peter for seconding Andys thoughts too.

I haven't seen the one at the museum working in person but from researching I have seen photos, they certainly look to perform very well and it's also a very nicely designed set from a serviceability view. I am currently in touch with a few restorers regarding the cabinet, I'd rather leave that to the pro's as I'd want any new finish to be sympathetic to the original. I do have a replacement front knob but one of the three to the side, along with its potentiometer stem extender, is missing too.

Once the cabinet is sorted I will consider where to go next but restoration would involve restuffing and finding correct period replacements for any other part. I know it won't get much use if restored anyhow other than an occasional run, one of the reasons why I'm still undecided, then gambling if the CRT is okay as CRM91's must be very very scarce.
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Old 15th Sep 2021, 5:04 pm   #5
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Default Re: 1938 Murphy A56V

I was the last person to have a go at the A56V at the museum which is currently working very well , here are a couple of Photos to encourage you
It might be worth your while to pay Dulwich a visit and we will get it out for you.
Regards Peter
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Old 15th Sep 2021, 6:14 pm   #6
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Default Re: 1938 Murphy A56V

Hi Peter, that looks lovely! I do visit London on occasion so I'll look at the possibility of viewing the set when I next plan a trip down. I'm sure if I seen it working in person I'd soon be wanting to get this one working
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Old 20th Sep 2021, 5:05 am   #7
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Default Re: 1938 Murphy A56V

Quote:
Originally Posted by EF80TVVALVE View Post
Hi all
There are a few period repairs but it is very much original which is making me consider leaving it as is. Although leaving it unrestored makes it nothing more than an ornament I do feel torn making repairs on such an early set. If I were to restore then it will have to be a very sympathetic restoration, restuffing caps etc.
From the photograph the period repairs match the post-war 1946 renovations (at the resumption of televison broadcasting after the war) that was done on my A56V and all other photos of other A56V/A58Vs I have seen. So it is very likely that they were done by Murphy or a Murphy dealer.

Your television looks to be in very good condition without any bits obviously missing, except for a missing rectifier valve on the Power Supply Unit. It is entirely up to you whether you decide to restore it, but if you do, some of the initial points below may be of help.

1. The Murphy A56V was specified to use two Mazda UU4 rectifiers. But when replacing the missing rectifier valve don't try to find a UU4, and instead replace with an UU5 (I obviously can't see what the other rectifier is but it is most likely a UU5 too). By 1946 Mazda sales literature listed the UU4 as discontinued, with the UU5 as the replacement. The UU5 was manufactured up until at least the late 50s and it is much easier to obtain.

2. The EHT wire (the yellow looking wire going from the PSU into a little tube on the CRT mount) is pretty thinly insulated for an EHT wire (and presumably hence the reason for the tube giving extra insulation where it goes close to the earthed chassis). Even though I prize originality, I replaced this with a modern high voltage lead, as it is always better to be safe than sorry with the lethal EHT.

3. The resistors used in the EHT bleeder chain (that removes the lethal EHT voltage after switching off) are very ordinary carbon types. They almost undoubtably will have gone open circuit (or at the very least extremely high). The television will operate without a working bleeder chain, but, it will be very dangerous to work on. Before turning the set on, you must ensure the bleeder chain is working for you own safety. When replacing, you should use resistors rated for 10K volts or above. I may be telling gradma how to suck eggs here, but, I think it is always best to raise this.

4. None (bar one) of the valves used in the television are very hard to obtain, the Mazda SP41's which form most of the valves were manufactured up until the mid 1970s, and easy to obtain. The one exception to this is the Mazda AC6/PEN (the line timebase output valve). This was specially introduced in 1938 for television timebase circuits, but obsolete by 1940 having been superseded by the Mazda PEN46. This means it is a rare valve, which doesn't turn up very often. So this is the first valve I would check for emission/performance just in case you need to find a replacement.

I spent three years restoring my A56V to fully working operation because mine was a wreck.

The thread detailing my restoration is here (https://www.vintage-radio.net/forum/...d.php?t=152108) if you've not already seen it.

I have put up some videos of the restored television on Youtube. The first (https://youtu.be/8XaaeC7idIQ) is using an original CRM92 CRT, and picture is a bit dim.

This video (https://youtu.be/QmU8_tkQ_z4) and this one (Dr Who for a change https://youtu.be/I2A7mzmsGx8) are using a rebuilt CRM92, and it shows the picture quality than can be obtained.
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Old 20th Sep 2021, 9:25 am   #8
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Default Re: 1938 Murphy A56V

Catkins, The picture quality with your new CRT is really excellent. I'm really jealous of the overall sharpness of focus.

Peter
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Old 20th Sep 2021, 9:50 am   #9
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Default Re: 1938 Murphy A56V

Quote:
Originally Posted by peter_scott View Post
I'm really jealous...
I'll say!

Didn't these pre-war tubes suffer from ion burn?

Steve
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Old 20th Sep 2021, 10:12 am   #10
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Default Re: 1938 Murphy A56V

The original tube fitted in the A56V was the Mazda CRM91 almost a 'wide angle' CRT with a 64 degree scanning angle. It looks squat when compared with the CRM92 and is noticeably shorter.
Most of these have been replaced with the post war CRM92 with modified mounting brackets.

A long while back I purchased an EKCO TS46. At the time I could not work out why the tube neck disappeared into the scan coils! The original Mazda label had it's data written in pencil. It was in fact a CRM91 fitted in 1953. That tube is is a real cracking tube now in a Murphy A58V owned by another Forum member. A good CRM92 was fitted in the EKCO from a scrap Baird portable.

The CRM91 in the A56V at the museum at some time passed been replaced by a CRM92 but the tube face was touching the implosion protection glass! This has since been modified. John.
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Old 20th Sep 2021, 10:55 am   #11
EF80TVVALVE
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Default Re: 1938 Murphy A56V

Thanks all for the replies.

Catkins, thanks for the advice and information, it's good to hear from others of things they experienced with their own restorations as it gives me something to look out for. I did read a previous thread that mentioned the EHT bleeder chain resistors so should restoration go ahead this will be a priority to ensure its repaired prior to switch on. I think the remaining rectifier is a UU5 from memory, I can't be certain until I check again!

The thing that does concern me with the set is the condition of the CRT, it looks free from damage but whether it is actually any good is an unknown. The set doesn't look to have had an awful amount of use so its in with a chance.

It also crossed my mind how close to the Wartime switch off that this set would have been sold, I can imagine spending a fortune on such a luxury to only have under a year of usage must have annoyed the first owners!
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Old 21st Sep 2021, 1:14 am   #12
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Default Re: 1938 Murphy A56V

Hi Catkins,
That's a nice clip of "The War Games", a story that drags a bit in places - but then joy of joys at the end, tardises everywhere, Philip Madoc and Harold Meaker

Cheers
Andy

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Old 21st Sep 2021, 3:08 am   #13
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Default Re: 1938 Murphy A56V

Quote:
Originally Posted by beery View Post
Hi Catkins,
That's a nice clip of "The War Games", a story that drags a bit in places - but then joy of joys at the end, tardises everywhere, Philip Madoc and Harold Meaker

Cheers
Andy
Another Dr Who fan

Yes it does drag a bit being 10 episodes, but, I believe it was a short notice replacement for some stories that fell through, and quickly written by Terrance Dicks and Malcolm Hulke. But I like it, and as you said the end episode with tardises, Philip Madoc and Harold Meaker is really good.

As we're in danger of going off topic, it's good to be able to say this story is notable (in television technology terms) as being the last Dr Who serial to be recorded in black and white, and exclusively transmitted on the 405 line system on BBC 1. The next serial of course being transmitted in 1970 with Jon Pertwee in 625 line colour.
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Old 21st Feb 2022, 10:19 pm   #14
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Default Re: 1938 Murphy A56V

Hi all,

I'm planning on making a start on the power supply of the A56V shortly, having been occupied by other projects I've only just begun to turn my attention to it again.

Firstly, I want to solve the problem of the EHT bleed resistors. As previously discussed they will need replacing as they are all high, the only problem is that I can't really find anything new that looks even faintly familiar to the originals fitted. I've added a somewhat poor photo of the types used so I'd like to hear different opinions on the way to go with this one, I'd like to keep it looking as original as possible and will be restuffing all caps, but this may be the only part where safely must overrule originality, luckily they aren't easily seen.
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Old 22nd Feb 2022, 10:04 am   #15
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Default Re: 1938 Murphy A56V

Hi EF80 TV Valve,
have a look at what I did with my HMV 905, see post #86

https://www.vintage-radio.net/forum/...=hmv905&page=5

Cheers
Andy
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Old 22nd Feb 2022, 2:46 pm   #16
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Default Re: 1938 Murphy A56V

Great stuff there Andy, I'll see if I can find a supplier of identical types that you used, I would imagine I'd have better luck finding 4.7meg rather than 5meg but I'll do some scouring online and see what comes up.
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Old 22nd Feb 2022, 8:26 pm   #17
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Default Re: 1938 Murphy A56V

Hi Bren, that style of carbon resistor tended to drift very high. If you can get a batch of old ones you may be able to select some that are close enough and repaint. That said they will then continue to drift high again. You should be able to get some modern high voltage types that are pretty small and hide them somewhere.

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Old 23rd Feb 2022, 10:46 am   #18
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Default Re: 1938 Murphy A56V

Hi Ed,
That was my initial thought but I had the same concerns and from a safety view I suppose it is best to have this section of the circuit working as reliably as possible. I have decided to follow Andy's idea and find some new manufacture that can be altered at the lead ends and painted to look closer to the originals. Whilst they won't have the hexagonal shape as the originals they can be made to look very similar and painted to match.
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Old 24th Feb 2022, 10:23 am   #19
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Default Re: 1938 Murphy A56V

Gosh, the speaker in this is a big as the tube itself!
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Old 18th Apr 2022, 9:31 pm   #20
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Default Re: 1938 Murphy A56V

Hi all,

Things are still moving with this set, albeit very slowly. First things first is to ensure that the EHT bleed will be working correctly before anything else. As was previously discussed I was having difficulty in finding replacement resistors that looked close enough to the originals. After Andy Beer's excellent suggestion in one of his previous threads I decided to take the same route and sourced some HV 5meg resistors and carry out the same modifications in order to create a more authentic look. There are 5 in total but at the moment the paint is still drying out on the others.

I've added a photo of the results as can be seen, I painted them in a dark matt green which is close to the originals but the picture makes them look much darker. I hope other members approve. I'll take some photos of the originals which they'll be replacing and although I can't make them in the pentagonal shape of the originals they do look quite authentic which was the aim.

The power unit is still in the cabinet, I'll be removing this shortly so I can continue work on it and make other repairs before starting on the main chassis.
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