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Old 14th Jul 2015, 1:51 pm   #81
Lloyd 1985
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Default Re: Murphy V180 restoration.

Mine also has poor frame linearity after changing all the caps, be interesting to see what's causing it!

Regards,
Lloyd
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Old 15th Jul 2015, 10:20 am   #82
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Default Re: Murphy V180 restoration.

Hi Lloyd,
I don't believe Murphy would have made a TV with such bad frame linearity as our sets display.
The anode load resistor of the frame oscillator thyratron has risen from 180Kohms to 270Kohms, it could one of the reasons for the poor linearity. It is R92 in the circuit diagram.
Also, I noticed that the only way the picture could be centred horizontally was to adjust the centring screws on the focus unit as far as they would go, in fact the whole assembly is at quite an angle relative to the tube neck.
This might suggest that a DC component is present is the scanning waveform, a 1 microfarad capacitor is connected in series with the scan coils, it might be leaky. This morning I reversed the leads to the line scan coils and sure enough the picture is now deflected to the right, this would certainly suggest that DC is present in the scan coils. So it could well be that the 1 microfarad capacitor is leaky, it is a waxie. C39 in the circuit diagram.

Another possibility is that the scan coil laminations are magnetised, this was discussed in a topic about a Pye BV20 which in fact had the picture shift problem.

DFWB.

Last edited by FERNSEH; 15th Jul 2015 at 10:27 am.
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Old 15th Jul 2015, 6:11 pm   #83
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Default Re: Murphy V180 restoration.

The frame linearity on the Murphy V180 should be 100%. Murphy Radio would never have produced a chassis with such poor lin.
I took this picture of my Murphy a few moments ago and it is good. It is operating with an Ekco T161 line transformer as I have been very lazy to fit the rewound transformer that is sitting on the bench, hence the line foldover on the left...
When David has finished his I will do the same with mine. Regards, John.
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Old 15th Jul 2015, 6:27 pm   #84
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Default Re: Murphy V180 restoration.

Hi John,
Absolutely perfect frame linearity. I'm convinced that my V180C will in due course display pictures just like your set. We know Murphy like Philips did things differently from other makers but there is no doubt their products did perform extremely well.

DFWB.
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Old 16th Jul 2015, 7:41 pm   #85
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Default Re: Murphy V180 restoration.

It has just occured to me that the first picture could have been the television test card on any receiver.
Just to back up proof that the Murphy can produce a linear picture, I have taken another with the 1947 V114 beside it. The V114 timebase is almost identical to the V180 other than it uses the earlier PEN45 valve in place of the later 6P25. The two valves are almost identical other than heater voltage and base. J.
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Old 16th Jul 2015, 10:37 pm   #86
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Default Re: Murphy V180 restoration.

After more fiddling with the frame timebase I've managed to secure an useful improvement, but it's still not perfect.
The line output valve in the V180C is the Mullard EL38. It seems strange that Murphy have chosen this valve because the traditional supplier of valves and tubes is Mazda and that companies' 6P28 would have been the obvious choice.
I've tried a Mazda 6P28 in the V180C and this valve works just as well as the EL38, in fact there is a slight increase of picture width and EHT.
The second picture shows the excellent interlace this set is capable of producing.

DFWB.
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Old 17th Jul 2015, 11:00 am   #87
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Default Re: Murphy V180 restoration.

A great result. Linearity, interlace and bandwidth all full marks.

Peter
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Old 18th Jul 2015, 8:49 am   #88
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Default Re: Murphy V180 restoration.

Hello David,
The EL38 valve is employed by Murphy Radio in the V180 due to it's smaller size. The 6P28 would have fouled on the CRT on the 12" models being mounted on the side in that odd way. It was all a matter of cramming it in to what was originally a 9" chassis.The lin looks very good and yes, the interlace is excellent on these models, a far cry from the V150.. John.
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Old 30th Aug 2015, 11:00 pm   #89
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Default Re: Murphy V180 restoration.

Yesterday I decided to try out various EL38 valves in this set, some Mullard branded and others Tungsram.

All was going well and then suddenly there was an almighty bang and the set stopped working. The fuses in the set weren't blown and on this occasion it was the 3 amp fuse in the mains plug that had failed. After replacing the fuse and a few quick tests the set was powered up again. You can see from the first picture the 220MFD HT smoothing capacitor has gone OC. The V180 does not have an HT reservoir capacitor, the cathode of the UU8 feeds only the smoothing choke. The reason for this is that this set operates on a much lower HT voltage compared with earlier models such as the V114.
The HT smoothing capacitor was replaced with a NOS component. The set was switched again and I was greeted with fireworks inside the UU8 and again more blown fuses. This time the fuse failure was caused by an HT short circuit. A real short circuit too, just a few ohms. Was it the "new" capacitor? It tested OK. In due course the short circuit was found. The Murphy circuit diagram shows a 0.005mfd capacitor, C26 across the HT supply.
Well I couldn't find C26 on the component layout diagrams.. However, another capacitor connected across the HT supply was found. In the V180 the screen grid of the 6F12 video amplifier is connected directly to the HT line and the offending capacitor is connected to that point. It was clipped out and the short circuit was gone.
A strange chain of events, the HT smoothing capacitor goes open and another capacitor shunted across the HT supply goes short circuit.
The set is working again and it seems that the UU8 has survived the HT short ordeal.
The third picture shows two different types of UK made EL38 valves. The one on the left is a Tungsram and does not have the appearance of a valve made by Mullard or Philips. The one on the right is a Mullard EL38 with the CV450 type number.

DFWB.
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Old 1st Sep 2015, 9:32 am   #90
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Default Re: Murphy V180 restoration.

It's my guess that the trouble was caused by the UU8 going S/C.
With AC applied to the capacitor, it was probably blown O/C. Check the UU8 valve holder for carbonization. The 'MURPHY NEWS' did mention this problem with the V114. This might have been the bang that you heard.
The 4v heated UU8 was a much more reliable Mazda rectifier than the later 80v U801 but when it fails it resembles a mercury arc rectifier!
I unpacked two brand new ones and both were S/C..Not a good record. Strangely the used, blacked and rattly ones I have are 100%.J.
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Old 11th Jun 2017, 12:20 pm   #91
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Default Murphy V180C cabinet.

The cabinet looks a lot better now than it did when I acquired the set in the summer of 2013.
The cabinet was designed for Murphy by Eden Minns.

DFWB.
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Old 11th Jun 2017, 12:43 pm   #92
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Default Re: Murphy V180C cabinet.

That looks rather smart young Sir, nice job !
It'll be nice to see it complete.

Marc.
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Old 11th Jun 2017, 1:18 pm   #93
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Default Re: Murphy V180 restoration.

Hi Marc,
I wasn't too sure how this set would finally look like, what with those black painted sides and detailing around the edges of the cabinet top panel.
But it seems designer Mr Minns got it right after all.
The chassis was tested last week, no drama but two of the front preset controls need replacement. Unfortunately, there is a tear on the loudspeaker cloth.
Fender combo amplifier cloth is similar. See attachment.
My thanks to Station X for merging my latest posts about this set with the original 2014 thread.

DFWB.
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Old 11th Jun 2017, 1:21 pm   #94
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Default Re: Murphy V180 restoration.

That cloth doesn't look bad at all, better than a torn original anyway.

Marc.
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Old 11th Jun 2017, 4:40 pm   #95
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Default Re: Murphy V180 restoration.

I was unwrapping my V180 a couple of weeks ago after it'd been in storage, and whilst looking at it I did think 'I wonder how David got on with his one...'. Your cabinet is looking rather lovely now, can't wait to see it all back together!

Probably about time I had another go at mine...

Regards,
Lloyd
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Old 12th Jun 2017, 12:32 pm   #96
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Default Re: Murphy V180 restoration.

Hi Lloyd,
Two of the front panel pre-set controls have failed, the 200ohm line linearity and the 100 ohm focus pots. Both are high wattage types with wirewound tracks.
A 250 ohm 3watt potentiometer has been found for the line linearity and the search is on for a replacement for the 100ohm focus control.
The focus control system is interesting. A permanent magnet is employed along with the focus coil for fine adjustment. The coil is in series with the sound output valve and the current is controlled by altering the cathode bias of the valve. A similar arrangement was used in some projection sets where a high slope pentode such as the EL41 was the focus control valve.

DFWB.
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Old 12th Jun 2017, 5:27 pm   #97
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Default Re: Murphy V180 restoration.

Those pre-set's aren't very good, I had 3 or 4 broken ones in mine when I got it, the most memorable being the line hold control, the wiper was missing, and the line stage wasn't doing anything, I bodged it with a piece of thick solder braid acting as a wiper, bought back the line timebase! I've just had a look through my stash of pots, unfortunately the only values I have are 10 ohm, 250 ohm, and 2X 1K ohm

With this focus arrangement, does it affect the audio at all?

Regards,
Lloyd
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Old 14th Jun 2017, 10:09 am   #98
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Default Re: Murphy V180 restoration.

"With this focus arrangement, does it affect the audio at all?"

It doesn't seem to be a nice arrangement, that is altering the bias of the output valve to achieve focus control. However, in practise there is no noticeable effect on the sound quality irrespective of the focus control setting.

The picture was taken yesterday. Still have that slight compression at the top of the raster.

DFWB.
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Old 20th Jun 2017, 11:54 am   #99
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Default Re: Murphy V180 restoration.

After about fifteen minutes the picture became dim, looked as if the CRT was low emission. Fault was easily traced to C28 going leaky. The capacitor is connected between the cathode of the vision interference limiter valve V6 and chassis.
The CRT in the V180 is grid modulated so any reduction voltage to that electrode will reduce the brightness.

DFWB.
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