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Old 19th Apr 2022, 8:22 am   #21
peter_scott
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Default Re: 1938 Murphy A56V

Definite approval here!

Peter
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Old 19th Apr 2022, 11:17 am   #22
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Default Re: 1938 Murphy A56V

Very nice resistors, just the job.

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Old 19th Apr 2022, 11:57 am   #23
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Default Re: 1938 Murphy A56V

Dark green is probably OK, but watch out for black paint which can be carbon-loaded!

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Old 20th Apr 2022, 7:03 pm   #24
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Default Re: 1938 Murphy A56V

I've removed the power supply from the cabinet and taken a few photos. I'll begin fitting the replacement bleed resistors and giving it a light dusting. I don't want to do much over-cleaning with it but it is absolutely caked in dust, cobwebs and hay! I need to replace the missing Mazda UU4 if anybody has one laying around, if not then I'll replace both for UU5's, but I'd like to keep it as original as I possibly can.

It is evident that the wiring inside the umbilical cable has perished and will need replacing. I initially thought that this was covered in rubber insulation but it turns out to be black fabric tape so it should be easy enough to replicate.

If anyone can supply a photo of the back cover of one of these sets then I'd appreciate it. This is missing and I'd like to make a replica so no fingers or paws find there way around the back once it's restored.
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Old 20th Apr 2022, 10:05 pm   #25
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Default Re: 1938 Murphy A56V

I have now fitted the replacement bleed resistors, they do look the part now they're fitted to the PSU. My attention next will turn to the umbilical cable and re-stuffing the 0.1uF capacitor on the EHT. Regarding the electrolytics on this PSU, what are others thoughts on these? They look to be in good physical order, will they likely reform and work okay or shall I consider re-stuffing these too? I'd hate for them to fail shortly after restoration and they are now over 80 years old but equally originality is important where possible.
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Old 21st Apr 2022, 11:10 pm   #26
beery
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Default Re: 1938 Murphy A56V

Those resistors look great!

I don't think I would trust any prewar electrolytics.
I do re-form 50s electrolytics using my own current limited re-former, which can gently do its magic overnight, but I've never had much luck with 40s electrolytics.
This is not so much to do with the condition of the rubber seal, but more to do with the fact that if left discharged, the electrolyte gradually corrodes the aluminium foil inside. After the capacitor has been without charge for a very long time, the corrosion causes irreversible damage. Then the leakage current can be enough for the electrolyte to boil and this of course will destroy the rectifier valves.
I say why take the risk, but re-stuff the electrolytics whilst the are nice and clean, rather than once they have piddled everywhere.

Cheers
Andy

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Old 22nd Apr 2022, 11:00 am   #27
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Default Re: 1938 Murphy A56V

Thanks for your thoughts Andy, they seem to echo mine too. They will l certainly look better restuffed as they are than when they fail and the bases have burst warts and innards spread all over them. It's quite funny, when I first started learning the repair of these sets just over 10 years ago, electrolytics were generally regarded to be okay during restoration until testing and not a replace on sight part. It seems we are now coming to an age where these also need to be replaced just as any other waxie as I have found on the last few early 50s sets I've been working on (unless I've just had bad luck more recently).
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Old 22nd Apr 2022, 1:32 pm   #28
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Default Re: 1938 Murphy A56V

Ah yes, the passage of time.
When I started collecting TVs over 30 years ago you could simply plug a 60's set straight in and you would get an almost perfect picture, though often with poor frame linearity. You probably wouldn't get away with it now. Just thinking about my first vintage set (a BRC 981 chassis) makes me feel very old.

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Old 23rd Apr 2022, 8:05 pm   #29
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Default Re: 1938 Murphy A56V

Hi all,

I'm about to embark on the next stage which will be to replace/restuff this EHT cap. Just before I begin does anyone have any opinions as to whether this is likely to contain PCB oil? It isn't Visconol branded and even then whether visconols do actually contain PCB or not is still up for debate. I have read that TCC were using PCB oil in some of their capacitors but that's as far as I got really.

I suppose the method of this is to just go about it very carefully and methodically. I have considered making a replica, any parts I take out will be saved with the set anyway, but it would be awfully difficult to replicate to a good standard.

Cheers
Bren
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Old 30th Jan 2023, 1:21 pm   #30
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Default Re: 1938 Murphy A56V

Thread reopened at OP's request.

Cheers

Mike T
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Old 30th Jan 2023, 1:46 pm   #31
EF80TVVALVE
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Default Re: 1938 Murphy A56V

Thanks for re-opening the thread Mike! It's been some time since I last looked at the A56V, to be honest it's not something I'm rushed to get working as I currently have a hoard of other projects I'm working through at the minute.

That EHT capacitor as shown on my last post has been hanging around waiting for me to re-stuff and I finally decided to make time and do it this weekend. It was a messy job so I didn't get a chance for any photos, I'm not too certain that this one did contain any PCBs. Unlike Visconol capacitors this had a soft yellow wax inside and it wasn't oil filled. Anyhow, it was all scooped out, cleaned up and a brand new 0.1uF 10kV capacitor fitted inside. I now have the power supply unit back in one piece after almost a year although it still needs more work.

The next task is to replace that very cruddy umbilical cord that provides power to the various circuits of the set. It is crumbling badly both outside and inside so before any power is given it needs replacing. Luckily I have some rubber tubing left over from some restoration work on my Pianola that is just the right size and colour so I'll be using this and threading the new wires through.

I'm quite tempted to give the set a tickle with the mains once I have this next job done and see if I get any life from it. Most everything else is still original other than the EHT bleed chain and the EHT capacitor so I'll be checking over the circuit for any obvious shorts or faults before I convince myself to do this as I don't want to cause any damage to any components.

I'm looking forward to seeing how the CRT behaves in this one. It's got that typical Mazda lack of getter, the heater lights up fine with a 2v supply so I know it's not completely gone to air but I expect it to be a bit flat or gassy.

More photos of the power unit:
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Old 30th Jan 2023, 4:05 pm   #32
Andy - G8MNM
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Default Re: 1938 Murphy A56V

Hi Bren,

Great job you are doing.

Please be very careful with that mains EHT! I know you will be.

Are you able to make a cover over the EHT rectifier valve top cap?

I have a HMV 2805 to restore/repair. It is the only TV that scares the S**t out of me at the thought of dealing with the lethal EHT!

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Old 30th Jan 2023, 4:21 pm   #33
EF80TVVALVE
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Default Re: 1938 Murphy A56V

Thanks Andy! I'm going to be very careful with it indeed, it does leave me slightly uncomfortable thinking about the mains derived EHT but equally I've never been stung by a regular flyback set either, as long as you are giving the set 100% of your attention when working on it then all should be fine. I work on some items at work that are generating 1500vDC from the mains so I'm quite used to similar dangers.

I have to admit when I've been stung by anything in the past it's because I've not been paying complete attention and it certainly teaches you a lesson. It's just important that before you do anything you're considering what you are actually doing and the possible dangers. I'm sure your 2805 will respond well, I remember your thread on the set and it looks like it will be a good one. Just ensure the EHT bleeder chain is working correctly and resistors still in spec, these are the only safety devices on these sets and they don't age well at all, hence why they were the first job on my A56V.

All the best
Bren

EDIT: yes the EHT cap could do with a top cap cover, I'll be looking into things such as this further down the line but I don't expect anybody to be poking their fingers in the set either. With that said it's important that I make a replica back panel for it ASAP. If anybody can help with some photos and measurements then that would be appreciated so I can make something close to the original.
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Old 6th Feb 2023, 10:09 am   #34
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Default Re: 1938 Murphy A56V

Interesting set, I wonder why they made the decision to angle the CRT?
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Old 6th Feb 2023, 10:38 am   #35
EF80TVVALVE
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Default Re: 1938 Murphy A56V

I'm not too sure but even sat on the sofa at home you're losing the very bottom of the picture under the glass plate, bit of an odd design really. Maybe sofas are lower than they used to be or did they expect you to be sitting in a very high arm chair
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Old 6th Feb 2023, 11:48 am   #36
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Default Re: 1938 Murphy A56V

Maybe they were going to launch a range of Murphy bar stools FM did go on to sell furniture!

Presumably it did allow them to lose some CRT depth and save money on the cabinet?
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Old 6th Feb 2023, 4:49 pm   #37
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Default Re: 1938 Murphy A56V

Quote:
Originally Posted by EF80TVVALVE View Post



EDIT: With that said it's important that I make a replica back panel for it ASAP. If anybody can help with some photos and measurements then that would be appreciated so I can make something close to the original.
Hi,
If nobody else should help, I would do this.
The best way the get a good reproduction is, to lay the original on a big scanner,
adding the measurements, and print it on the right cardboard.
With some special stamping irons, it will be possible to cut the holes into the new panel.
This might be the biggest investment.

P.S. Where did you bought the 10000 VDC cap?

Regards,
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Old 6th Feb 2023, 9:09 pm   #38
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Default Re: 1938 Murphy A56V

Attachments show the two backs from my Murphy A58V. I think the larger back also fits the A56V. The height of the two backs is 24inches.
From memory the larger back is 14" wide and other is 11 1/4" wide.
PM me if want more precise details.

DFWB.
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Old 6th Feb 2023, 9:14 pm   #39
EF80TVVALVE
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Default Re: 1938 Murphy A56V

Wd40addict, yes I think you may be right there, hard to say exactly why they did this but there must have been a reason and yours sounds the most likely I should think. Funnily enough a bar stool would give you just about the perfect viewing angle really!

German Dalek, I hope somebody can come forward and help with the back, it's shame it's missing but in a mains derived set it is an important safety shield too and that needs to remain. I have never seen the back to one so I have no idea what they look like. The 10000v capacitor I bought online, if you search 0.1uF 10000v capacitor into your search engine it should come up with a few results. I think I bought it from an American supplier but it was a short while back now and I can't remember clearly who it was from!

Edit: looks like our posts crossed David, thanks for sending some photos and approximate measurements. I'll measure up the size of the A56V and see if it matches. Just seeing what one looks like should be enough to go off I think. It doesn't have to be an exact copy but something close would be good.
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Old 7th Feb 2023, 5:55 am   #40
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Default Re: 1938 Murphy A56V

Quote:
Originally Posted by EF80TVVALVE View Post
I hope somebody can come forward and help with the back, it's shame it's missing but in a mains derived set it is an important safety shield too and that needs to remain. I have never seen the back to one so I have no idea what they look like.
I have attached some photos of the back of my A56V. One has some rulers added to hopefully give a better indication of sizes and positioning.

The size of the back is width 14 inches (35.5 cm) and length 6 1/8th inches (74 cm).

PM me if you want higher resolution photos that can be attached here.

Catkins
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