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Murphy V849U ( Includes the RBM LOPT Overwind Cure)

Pre War 240/405, Post War 405 Line, B&W Dual Standard, Colour Dual Standard, B&W S/S 625, Colour S/S 625 line, Hybrids. Standards converters & modulators, video recorders.
 
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Murphy V849U ( Includes the RBM LOPT Overwind Cure)

Post by PYE625 » Fri Sep 04, 2015 2:59 pm

Hi, well after a ride over to the fair city of Norwich, I am now the owner of the above set.
Here are some pics of the chassis complete with dust, but looks to be missing a metal screen from the lopt area.
Also has an RS polo on one of the dropper sections, plus a transistorised UHF tuner fitted.
Probably a re-gun tube....CME1903 "ANGLIAN" ?
Attachments
rsz_001.jpg
rsz_002.jpg
rsz_003.jpg
rsz_005.jpg
rsz_006.jpg

 
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Re: Murphy V849U

Post by nuvistor » Fri Sep 04, 2015 4:01 pm

Good news on the transistor UHF tuner, that made a big improvement to the performance on 625 lines.
Anglian CRT, I would agree a rebuild but if it is a good one it does not matter. Has from an earlier post I think Murphy use Mazda CRT's and in the 60's I found them much more unreliable than Mullard.

It appears to have had little work done to it, I cannot remember if that was the original thermistor location or the modified one. Flywheel sync diodes look like replacements however those were still the troublesome type but the interlace looks original. I used 1N4148 diodes with 15k to 22k resistors as per Rank modification. If you don't use the resistors the line hold will have too much lock in range and the frame interlace will be impaired.

Look forward to seeing a working set.
Frank

 
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Re: Murphy V849U

Post by PYE625 » Fri Sep 04, 2015 5:07 pm

You won't be waiting long Frank.....
Re-formed the main electrolytics, cleaned it out a bit and all ready to go? dmm

Just replaced these three sweaty waxies and then first light on 405...
Attachments
rsz_001.jpg
rsz_004.jpg
rsz_4005.jpg

 
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Re: Murphy V849U

Post by nuvistor » Fri Sep 04, 2015 5:27 pm

The tube looks good and so does the picture .

 
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Re: Murphy V849U

Post by ntscuser » Fri Sep 04, 2015 5:45 pm

Blimey that was quick! :ccf

Looking good so far :aad

I'm not familiar with that chassis but it appears to be hand wired rather than printed circuit boards?

 
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Re: Murphy V849U

Post by PYE625 » Fri Sep 04, 2015 5:52 pm

And here is 625....lets hope the LOPT holds out :aaq

The chassis is wired and no PCB'S :bba
I'm not familiar with the chassis either, and this is the first time I have had the pleasure to own one.

Obviously a bit of work to do, but not many caps to replace...think those three were the only wax types.
The dropper section needs tidying and modifying if needed, will look at that in time.

According to the seller, the set was found in a bedroom of a house recently cleared due to the death of the owner.
The set has survived pretty well I think.
Attachments
rsz_008.jpg
rsz_1003.jpg

 
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Re: Murphy V849U

Post by mark pirate » Fri Sep 04, 2015 6:56 pm

According to the seller, the set was found in a bedroom of a house recently cleared due to the death of the owner.

It was probably working when put away, the owner probably replaced it with a colour set in the 70's
Looks like a cracking set, stored in a nice warm bedroom, fitted with a rebuilt tube AND has a good LOPT!
It certainly was a lucky find :aad

 
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Re: Murphy V849U

Post by marc » Fri Sep 04, 2015 6:58 pm

Hi Andrew,

Well what can one say, yet again another cracking find young Sir ! :aad
Very well done indeed :bba

Cheers,
Marc.

 
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Re: Murphy V849U

Post by neil29 » Fri Sep 04, 2015 7:24 pm

The one I acquired a while back just worked when I plugged it in :bba although it's pot luck as to whether the lopt lasts :aaj :aak .

Cheers
Neil.

 
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Re: Murphy V849U

Post by PYE625 » Fri Sep 04, 2015 11:50 pm

neil29 wrote:The one I acquired a while back just worked when I plugged it in :bba although it's pot luck as to whether the lopt lasts :aaj :aak .

Cheers
Neil.


Well, after about half an hour when using 625 lines, the width does start to shrink.
So, I will apply the procedure to the overwind and see if it will dry out a bit.

I also carried out the mod for the thermistor re-position.
Attachments
rsz_006.jpg
rsz_005.jpg

 
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Re: Murphy V849U

Post by Terrykc » Sat Sep 05, 2015 1:00 pm

nuvistor wrote:... Anglian CRT, I would agree a rebuild but if it is a good one it does not matter. Has from an earlier post I think Murphy use Mazda CRT's and in the 60's I found them much more unreliable than Mullard ...

Our Mullard rep used to refer to that as Mazda's 'built in snuffer'!

The tubes went flat, typically when they were 15 to 18 months old, so outside the 12 month guarantee period.

When Rank took over Murphy, the latter must have had existing contracts with Thorn so RBM fitted Mullard 19" tubes and Mazda 23" tubes in both marques. The rep told us of one large dealer in the Southend area who had over 200 23" sets out on rental that needed new tubes!

On his next visit he wasn't so happy. The firm had taken the matter up with Mazda who had agreed to replace the tubes but only on condition that they signed a bulk supply agreement for Mazda to supply all their valves ...

The next thing that happened was a flurry of advertising from Mazda about their new extended two year guarantee on CRTs!

 
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Re: Murphy V849U

Post by PYE625 » Sat Sep 05, 2015 2:05 pm

Hi Terry,
It sure is a re-gun and has a good bright and sharp picture.

Been having fun trying to set up the line hold though. Can set it fine on either standard, but the difference between standards is miles out. Have been through the set-up for line hold several times now to no avail, there must be a fault.

Interestingly, the so-called 625 line hold preset RV33 affects the 405 line hold just as much as it does on 625.... :aaq

Ignore all that about the line hold.....dumbo here has mixed up which control is which !!!!!!! :zx:
Attachments
rsz_002.jpg
rsz_003.jpg

 
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Re: Murphy V849U

Post by PYE625 » Sun Sep 06, 2015 9:22 am

Well, after what looked a good start I'm afraid I think the LOPT is kaput.
When cold, the set works normally with roughly correct HT voltages. After a few mins, the width will start to shrink and HT drops.
It is the line stage dragging down the HT. The overwind gets a little warm to the point of being slightly soft, but not melting.
I tried leaving the overwind powered up overnight with 30VDC to try and dry it out, but no difference..... :aai

 
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Re: Murphy V849U

Post by sideband » Sun Sep 06, 2015 9:43 am

Candidate for a solid state EHT rec I think. Take the overwind off completely and use an EHT stick.

 
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Re: Murphy V849U

Post by Cathovisor » Sun Sep 06, 2015 9:56 am

Given the set's superb condition, wouldn't this be a candidate for that nice Mr. Barker to do one of his rewinds on? Ships and ha'porths of tar come to mind here...

 
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Re: Murphy V849U

Post by PYE625 » Sun Sep 06, 2015 10:08 am

Here is the poor 'lil LOPT....overwind seen better days lol.
It looks to be possible to dismantle without damage, so I could try the doubler trick and keep the overwind for a rainy day.
I would like to keep the set original, so a rewind is on the cards.
Attachments
rsz_001.jpg
rsz_002.jpg
rsz_003.jpg

 
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Re: Murphy V849U

Post by PYE625 » Sun Sep 06, 2015 12:01 pm

Hi, I removed the overwind and substituted a doubler which has restored normal operation on 405.

However, within the overwind, there is another smaller coil that is switched in for 625 operation.
You can see the connections in the yellow sleeve on the overwind.
I am in fact wondering if it is high voltage leakage to this winding that is the problem.

The point of the exercise is to prove beyond doubt that it was the overwind....and surprise surprise, it is.

I have removed the tar covering and will let the overwind boil steadily with some DC volts across it....whether it will be ok after some time, well, I will just have to wait and see.

The doubler in situ is not as pretty as the DY86 !!
Attachments
rsz_002.jpg
rsz_003.jpg

 
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Re: Murphy V849U

Post by PYE625 » Sun Sep 06, 2015 12:32 pm

Well well well.....
In the post above, I said about the small winding contained with the overwind that is switched in on 625.
It is of low resistance and is connected to ground at one end.

When I measured the continuity with a DVM between the two windings it is open circuit as you would expect.
BUT...when a voltage is applied to the overwind alone, a voltage appears at the other winding too.
For example, using 500vdc on the overwind produces about 70vdc on the other winding.

This is leakage and it increases with the temperature of the overwind.
When the overwind is cool, there is NO leakage between windings.

Now....what to do about it?
Can I pull off the overwind section and possibly improve the insulation between windings?? :aaq

 
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Re: Murphy V849U

Post by PYE625 » Sun Sep 06, 2015 2:56 pm

Yes, I was able to separate the overwind from the former which has a small winding on it.
It was only possible to remove when quite warm, being heated by approx. 35 vdc across the overwind for a few mins.

First pic. is of the rather messy overwind with the paxolin former removed.
I unwound the fabric tape that is meant to insulate the small inner winding from the overwind.
I used kapton tape and then polythene tape to replace the old fabric tape, being careful to maintain a suitable thickness so the former would still fit back into the overwind doughnut.

I re-assembled the LOPT and tried it out.....SUCCESS!!
HT is normal, width is normal and the set has been on 625 for nearly two hours without any re-lapse.

So, could this be a solution to the dreaded Bush sick LOPT problem?
Attachments
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rsz_003.jpg
rsz_005.jpg
rsz_006.jpg
rsz_009.jpg
rsz_1002.jpg
rsz_001.jpg

 
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Re: Murphy V849U

Post by neil29 » Sun Sep 06, 2015 3:47 pm

With any luck you may well have sorted it :bba . but only time will tell.

Cheers
Neil.

 
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Re: Murphy V849U

Post by CTV » Sun Sep 06, 2015 5:32 pm

What a great result and an outstanding piece of detective work Andrew. If it holds up on soak and is proved to be the main culprit these LOPT's face, we may just have the solution now. :thumb

 
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Re: Murphy V849U

Post by PYE625 » Sun Sep 06, 2015 5:47 pm

CrustyTV wrote:What a great result and an outstanding piece of detective work Andrew. If it holds up on soak and is proved to be the main culprit these LOPT's face, we may just have the solution now. :thumb



Cheers Chris,

So far so good...been about 5 hours so far on soak running on 625, but as Neil said, time will tell lol.

 
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Re: Murphy V849U

Post by PYE625 » Sun Sep 06, 2015 6:32 pm

On a slightly different note, this set has a transistorised UHF tuner fitted.
I would guess it would have had a valve UHF tuner originally ?

Anyway, a check on the valve heater voltages suggested they were too high the PCL82 was at about 17v whereas it should be 16.
I worked out that the PC88/86 of a valve tuner should drop about 7.5 volts, so I fitted an additional 25 ohm resistor in the heater chain.
This means that all the heater volts are now correct.
I mounted it on the UHF tuner plug, and it doesn't get very hot. There was just a wire link fitted across the heater terminals before.
Attachments
rsz_007.jpg

 
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Re: Murphy V849U

Post by sideband » Sun Sep 06, 2015 7:16 pm

What a fantastic piece of detective work and diagnosis! :aad

Maybe most of the Bush LOPT's can be salvaged in this way.

Brilliant... ttt:

 
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Re: Murphy V849U

Post by nuvistor » Sun Sep 06, 2015 7:17 pm

Worth checking the current rather than the voltage with it being a series heater chain rather the voltage across an individual valve just in case that valve heater is not quite right.
I reconditioned an Ekco T433 in 1970 for use as our home TV. We always have had a good mains power supply, usually 250v, I measured the series current and found it high, fitted an extra 20 ohm to bring it to 300ma. The last time I measured the power quite recently is was 253v, not using the T433 anymore though dmm

Frank
Edit,excellent result on the LOPTX

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