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Old 23rd Jun 2019, 10:43 pm   #1
sexton_mallard
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Default Murphy V2023

I came upon this set on my car boot scouting today. It is in good cosmetic condition apart from a pong of nicotine and needing a good deep clean. A quick google reveals this set was a bit of an Austin Allegro of the TV world what with LOPT failure being a common problem. On the other hand I have not seen a hybrid single standard 20 inch set before...I felt lucky for a change and bought it for a tenner. What struck me the most was how much of a space saver a 110 degree tube is... the set looks relatively compact.

On initial inspection, the tuner has the usual broken plastic collets stopping the channel buttons from latching, everything inside looks intact and unmolested. The set has a Mullard A50-120W/R CRT which bodes well from comments I have read about these sets with Mazda tubes. (The tube label was found on the bottom of the cabinet). The LOPT appears to still have a valved EHT rectifier.

The LOPT looks relatively modern with plastic or epoxy potted bobbins as opposed to pitch/bitumen/wax which bodes well. The big question is do we know what caused the LOPTs to fail in these sets in the day? Was it the operating conditions the LOPT was placed under or just poor QA of the LOPT manufacture? Where I am coming from is I want to ensure the operating conditions are ideal for when I power this set up (very carefully).
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Last edited by sexton_mallard; 23rd Jun 2019 at 10:50 pm. Reason: Fix typos
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Old 23rd Jun 2019, 11:28 pm   #2
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Default Re: Murphy V2023

The earlier pitch type in some cases appears to be a breakdown of an insulation layer between windings and some have repaired the transformer by stripping down and replacing the insulation.
Not sure why the more modern style failed, but it did..
https://www.radios-tv.co.uk/bush-murphy-lopt/
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Old 23rd Jun 2019, 11:54 pm   #3
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Default Re: Murphy V2023

The A774 wasn't brilliant reliability or performance wise. While most manufacture's single standard sets were better than their dual standard models due to less complexity and not having to compromise between systems the A774 was less reliable and had poor performance compared to the previous A640 model.
The A774 seemed to be a little inconsistent, on some the picture looked flat and grey others were better. If you set a poor one up the next time you saw it the picture had gone grotty again.

The brightness and contrast seemed to wander about leaving some scenes dark and others milky.
The LOPTs weren't all bad I have a A774 in my collection still on it's original transformer still working.
The 20" and 24" "Square screen" CRTs often suffered from poor focus around the edges of the screen. Later Mullard tubes were not as good as the earlier 19 and 23 inch.
My set had a low tube the picture was poor and had a tendency to go slivery on the highlights. I took a chance and gave it a boost with my home made booster and as yet it has held up a treat.
To give the LOPT it's best chance I would check all of the capacitors in the line stage for leakage and keep the boost pot as low as possible whilst still giving full picture width.
I used to tweak the magnets on the scancoils for max width so the boost pot could be backed off a bit.
A bit of a heap when they were current but a good set now for a vintage TV collection. Every classic car collector should have an Edsel!


Rich.

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Old 24th Jun 2019, 12:00 am   #4
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Default Re: Murphy V2023

I've got a V2023 and it has had a new lopt with a stick rectifier installed at some point. and most of my A774's do have the original lopts in them and seem ok at the moment but I wont hold out much hope of them working permanently .

Cheers
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Old 24th Jun 2019, 1:53 am   #5
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Default Re: Murphy V2023

I did an A774 thread a while back, certainly not the best set in the world. Like others have said, expect line out problems. I had arcing from the overwind to the heater winding. I replaced the the EHT rectifier valve the a stick rectifier.

My CRT was also low but responded to a tickle ok. I must dig it out a see if it's still working...
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Old 24th Jun 2019, 8:22 am   #6
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Default Re: Murphy V2023

There were several official mods/reliability during the course of production of the A774 chassis and these made a useful improvement to the performance of the set. In particular, an additional small preset variable resistor was added in order to optimise the vision AGC operation.

Apart from what has been mentioned in the preceding posts:

The two vertical stiffening metal rails that run from top to bottom of the chassis (on the components side of the PCB) and which are soldered to the copper print in several places, tended to become dry jointed, leading to all sorts of strange effects. So make sure you rework these.

The original LOPT/EHT rectifier assembly was eventually replaced by a type using a small voltage doubler, in place of the DY802 valve.

It will be wise to replace any paper dielectric capacitors in the LOP and frame output stages, with modern Polypropylene types (such as the boost HT reservoir capacitor). The mains filter capacitor should also be replaced.

The plastic formers of the scan coil windings tended to disintegrate over time.

Check the values of the fixed resistors and "set Boost HT" preset pot in the width stabilisation circuit.
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Old 24th Jun 2019, 11:08 pm   #7
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Default Re: Murphy V2023

Hi Dom,
What an excellent car boot find and a good looking set too!

I assume, unlike the A640, that the DC component of the video is not maintained to the CRT cathode? Coupled with mean level AGC, I don't doubt the picture contrast is all over the place!

My Thorn 1500 (courtesy of Neil!) has the same tube and produces an excellent, well focused picture, especially after adding a black level clamp, so I'm sure the Murphy can be made to do the same!

I'm sure one cause of LOPT failure that seems to get overlooked, is heat. I have spent some considerable time trying to get to the bottom of this problem. Almost all my sets suffer from this issue to a greater or lesser extent. As the transformer warms up, it gets to a point of thermal runaway. This usually takes about an hour and once the heat builds up to a certain point, it rapidly escalates to the point of melting wax etc.

Whether its the resistance of the windings, or leakage between layers, I don't know. Transformers have little ability to loose heat and are often mounted where there is no ventilation anyway.

I find if you can keep the initial heat build up down, the transformer will stay almost cold for hours on end. My solution, therefore is to mount a small cooling fan near it powered from a small transformer.

This works really well and also keeps the EHT at the correct level.

Good luck with the restoration,
All the best
Nick
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Old 3rd Aug 2019, 8:09 pm   #8
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Default Re: Murphy V2023

It's a runner (for now)!

I snipped out the across-the-mains cap then did some basic checks. I cleaned the eht wire and the anode connecter on the back of the screen and refitted it and then applied power gradually via a bulb limiter. Finally on full voltage I get sound, and a really bright raster!

Trying to find the brightness control to turn it down. There is a very faint sizzle from the LOPT but it is a humid day, the set has been stored in a warm dry place for the past few weeks. I downloaded the July 1977 Television magazine guide for the circuit and common faults descriptions. Next, to carry on checks and recap around the line and frames stages. The electrolytics are dated 1972.
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Old 3rd Aug 2019, 8:30 pm   #9
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Default Re: Murphy V2023

Looking good so far, tube seems brighter than mine.
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Old 3rd Aug 2019, 9:35 pm   #10
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Default Re: Murphy V2023

Thanks John Joe.

The source of the quiet sizzling appears to be around the top of the DY802 valve holder. See the light blue ring of discharge. The rectifier and holder are pretty grotty, coated in what looks to be a soot/nicotine mixture and will be cleaned (making sure the tube is discharged first!). There is snow displayed on the screen and all the controls on the back respond fine.
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Old 3rd Aug 2019, 9:56 pm   #11
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Default Re: Murphy V2023

Mine was the same but no amount of cleaning would solve it, hopefully you'll have better luck. I'd still be tempted to bin it in favour of a stick rectifier.
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Old 3rd Aug 2019, 10:31 pm   #12
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Default Re: Murphy V2023

Not my favourite set, 1500's seemed to show better pictures. I repaired a lot and I also never changed a line transformer. They had a bad name for this. The 161 was a totally different matter, and the Philips 210, always failing. My main bleat with the 774 was low tubes.
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Old 4th Aug 2019, 7:33 pm   #13
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Default Re: Murphy V2023

Quote:
Originally Posted by linescan87 View Post
Mine was the same but no amount of cleaning would solve it, hopefully you'll have better luck. I'd still be tempted to bin it in favour of a stick rectifier.
Hi John Joe, that would make good sense as the DY valve is beneath the LOPT and probably heats it up. Could I make up a diode using say a high voltage type? I reckon I'd need to check and monitor the EHT voltage after the modification. For now, I'll try a cleaning session.
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Old 4th Aug 2019, 7:46 pm   #14
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Default Re: Murphy V2023

You could probably put a few high voltage types in series, someone smarter than me will confirm. I'm sure someone will have a spare stick rectifier if you ask. I may have one, though I'd have to look..
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Old 4th Aug 2019, 9:16 pm   #15
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Default Re: Murphy V2023

The original valve can easily be retained. Providing the heater loop in in good condition and the soldering on the valve base is tidy it shouldn't arc unless the EHT is high.
There used to be a stick rectifier "mod kit" which did away with the heater winding and replaced the EHT lead. It was a "universal" fit and could be used on other models as well, the PYE 169 and Philips 170 series spring to mind .
Handy as a field service bodge to get you out of the house but not really the done thing now when time is no problem.
The heater loop is easy to replace with a little care if necessary. If the EHT is high or there is a dampness problem fitting a stick won't help.

Rich.
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Old 13th Jun 2020, 12:18 am   #16
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Default Re: Murphy V2023

Thread reopened by request.
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Old 13th Jun 2020, 1:02 am   #17
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Default Re: Murphy V2023

I finally caught up with this set and treated it to a 2kv rated boost cap and replaced the across the mains cap and gave it a run. After about an hour and some twiddling with the linearity pots I get a reasonable picture...just the vertical bar generator from the HDMI2AV converter via a uhf modulator. The smell from the formerly damp chipboard and all the warm chassis is fairly fruity! The picture is stable after 2 hours and the discharge around the HT rectifier valve holder has gone. Tomorrow I will replace the 2 1kv caps in the line stage area and treat this set to some actual broadcast. I hope this shames the K B RV10 into working for me next...
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Old 13th Jun 2020, 1:06 am   #18
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Default Re: Murphy V2023

A picture of the screen...
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Old 13th Jun 2020, 10:44 am   #19
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Default Re: Murphy V2023

The tube in this set seems brand new! contrast is all the way up with the brightness set half way. There is rustling on the audio but the sound quality blows away any panel TV I have heard...an A774...

Linearity is still off with an egg shaped picture but I see what you mean about the picture quality. The picture bounces a little bit from dark to light and no black level. Probably the focus is the one thing that bothers me the most. Trying to read the on screen captions of the NowTV dongle is a struggle. Let's see if I can improve this.

I'm probably lucky. The shop floor got a pay rise that week and the MD was hovering around in the QA department that day. Then this set spent most of it's life in a back room not being used much. The PL504 LOP and PY88 are Pinnacle branded and I assume are replacements. How much use does it typically take for these valves to be replaced?
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Old 13th Jun 2020, 11:25 am   #20
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Default Re: Murphy V2023

It's difficult to say how long the original line output valves would have lasted often valves were replaced unnecessarily. If a set had an intermittent fault a busy field engineer would take an educated guess and pop in a couple of "bottles" with the remark "see how it goes..." many valves were prematurely replaced I think.

When I worked for a rental company one of the engineers would replace valves that looked old and heat stained as he thought it would save breakdowns in the future however I have found that many old heat marked "old looking" valves are still fine.
To replace say a Mullard with a far eastern made cheapo probably would do nothing to improve reliability. My service manager always shopped around for the best prices. Some Solus branded valves were not very good but they were cheap...

A way to see how much use the set has had would be to look at the original valves a well used PCL805 or PCL86 will usually show signs of heat marking. Also the general appearance of the set inside, heat staining around valve bases. The condition of the solder on the high wattage "dropper" resistors (I think there are two white ceramic block types on this chassis) are all signs of use.
My mate had a new old stock Thorn 1500 some time back it absolutely sparkled inside ! I had never seen a new one inside as they were all a few years old by the time I saw them.
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