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Old 19th May 2015, 8:00 am   #41
Heatercathodeshort
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Default Re: Murphy V114 9" table model 1947

Ha! ha! Quite a compliment! This really was a beastie that fought to the bitter end. All the faults other than the tube were down to storage and sheer age. I guess the failing emission and the super bright pictures produced on the 1958 V410 series must have pushed the owner into buying a new model plus of course the addition of Band 3.
It's lucky it survived. Old receivers were usually taken away by the dealer when installing the new one and smashed up especially if they were faulty.
This is one that got away but it was a close thing! Regards, John.
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Old 19th May 2015, 9:05 am   #42
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Default Re: Murphy V114 9" table model 1947

Quote:
Old receivers were usually taken away by the dealer when installing the new one and smashed up especially if they were faulty.
Sadly that was probably the fate of the Bush T57 that I grew up watching, it was taken when the dealer delivered it's replacement

Those EA50's are strange little valves. Although I have a signal generator with a couple in it, I am yet to get a TV fitted with them.

Glad to see that the Murphy is reluctantly succumbing to your skills, I look forward to seeing the final result.

Mark
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Old 19th May 2015, 6:39 pm   #43
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Default Re: Murphy V114 9" table model 1947

We now had a servicable CRT, video output, detector and two vision I.F. amplifiers working to an extent that a decent signal should pass through them in a fashion similar to a warm glass of ENO Fruit Salt. [Now who remembers that?]
It was time to once again supply the front end with the full power of the Aurora switched to channel 1. To my surprise absolutely nothing came through with the sensitivity, contrast and volume controls on full.

I began to wonder if the front end had been converted to Sutton Coldfield in an attempt to obtain a better signal provoking a very close examination of the aerial and oscillator coils.
Sure enough L4 the oscillator coil had been replaced by the dual channel coil with a tap for the higher frequency. Removing the screening cans from the aerial and anode tuning coils, L1/L2 and L3 revealed they were all equipped with brass cores to cater for the higher channel 4 frequency. [The original channel 1 coils are iron dust]

The full output of the E2 was connected to the aerial socket and it's output frequency rocked around 40 to 60 mc/s. Nothing...no hum, squeak or ripple. Unbelievable!

In desperation I replaced the 6D2 [EB91] frequency changer, all to no avail. [Now I know the true meaning of MURPHY MADNESS]

The reliable 6L18 local oscillator more familiar sitting lonely in EKCO spot wobble sub chassis, came under suspicion. A meter check on its anode showed approximately half the figure quoted in the manual, only 26V and I instantly jumped to the conclusion that this was the cause of the non oscillation..
A new 22k 1 watt anode load was soon soldered into place. The original read 70K.
This time with the mains applied and with the E2's output swung around 58mc/s a low level tone could be heard from the speaker. At last we had signs of life but rocking the generator up to the vision frequency around 60mc/s produced nothing!
How silly can it get? With the generator reset for the sound frequency the receiver's oscillator core was adjusted slightly towards the vision frequency. With a faint 'plop' the oscillator stopped. Obviously 60mc/s was just too much to ask for a 68 year old 6L18 that was firmly stuck in it's B8A holder. This required considerable effort and a squirt of WD40 before it finally popped free.

Luckily I had a very old 'new old stock' example still in it's vintage box. I must admit I hate disturbing these lovely old packages but if they are needed in service it just has to be done. It clicked nicely into position and once again the AURORA set to channel 4 was brought into service. The new 6L18 was more than happy to sing well above 60mc/s and my confidence returned.

We had sound, not much of it and distorted into the bargain but it was real 405 line test card music that woke the good quality speaker from its slumbers.

Can you imagine my surprise to now see a frame collapse on the screen...I pushed the T41 and PEN 45 well into their sockets and looked for any disconnected wires but the frame timebase refused to scan.
When was this nightmare to end?
I pulled out the aerial connection to gain better access to the frame timebase section of the rear chassis and to my surprise the frame scan returned. Plugging it in again produced a collapse. I know of Plessey chassis that do the reverse but not with the signal applied!
It took me a while to work out what was happening. The sync separator in the V114 series is a double diode. It is actually a very good circuit producing clean frame sync pulses for good interlace. The frame sync pulses actually pass through a choke/capacitor filter similar to the standard HT smoothing circuit that eliminates any trace of the line sync pulse.
The strapped anodes are connected to the cathode of the video amplifier via a .5uf capacitor in parallel with a 4.7M resistor. The .5uf turned out to be completely S/C resulting in the DD41 double diode acting as a rectifier placing a DC voltage on the grid of the frame thyratron generator, blocking its operation. The application of the sync pulses must have tipped it just over the top resulting in the total collapse.
The capacitor was mounted on the back chassis upright in a diabolical position surrounded by two fat wire wound H.T. distributors. No wonder it gave in.
With a new capacitor in place it was just about possible to make out a very distorted test card C. The sensitivity was on full and any attempt to reduce it resulted in a fade out.

Recalling the sage with the duff 6F12's I slipped in a replacement R.F. amplifier EF91 to be presented with a complete vision overload! Yet another 6F12 had died on me leaving just the sound IF amplifier original. With the sensitivity and contrast backed off a recognizable picture was presented. It was certainly not up to the high standard expected from Murphy Radio but there was plenty of donkey work to complete before it gave its full glory.
The cogged and out of shape test card show how it looked after replacement of a number of components in the line generator/output stage, notably C59 .02uf in the line damping [linearity] circuit, R82 width pot 200 ohms and R67 390 ohms. The later was only slightly high at 450 ohms but it's replacement centered the line hold control.

With an encouraging result I now felt it safe to replace all remaining wax paper capacitors. They were all leaking badly, just a routine job but great care has to be taken to avoid man made faults!

The pictures show the coverage of the BBC Sutton Coldfield transmitter showing Wellingborough on the fringe from both AP and SC. A much more reliable signal would have been obtained from Sutton Coldfield with less fading provoking the change from the original Alexandra Palace frequencies. The double diode sync separator showing the shorted coupling capacitor in red and the elaborate interlace filter in green. The test card shows the results after a lot of twiddling...The next write up will probably be the concluding one. Regards, John.
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Old 19th May 2015, 7:55 pm   #44
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Default Re: Murphy V114 9" table model 1947

Nearly there then, John.

We wait with baited breath for the next thrilling instalment!
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Old 20th May 2015, 8:39 am   #45
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Default Re: Murphy V114 9" table model 1947

Quote:
Now I know the true meaning of MURPHY MADNESS
I am quite surprised at how many 6F12's have given up the will to live!
Was the Mazda 6F12 as unreliable as the Marconi/Osram version (Z77)?
I had to replaced several Z77's in my Marconiphone VRC74DA with the nice blue Mullard EF91's.

Let's hope the remaining 6F12 survives all those new capacitors being installed!

Mark
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Old 20th May 2015, 9:27 pm   #46
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Default Re: Murphy V114 9" table model 1947

No Mark, Unbelievably the sound I.F. amplifier also proved to be faulty!
It is my personal opinion that the MOV/Osram Z77's are a poor quality valve. The HMV 1902 at the museum required replacement of all but one on the R.F. unit and I have had a large quantity faulty in the 1807 series.
Over the years I have not seen many Mazda 6F12s. They were soon superseded by the 6F1/13 around 1949. Knowing Mazda's reliability for valves of this type I think it was the poor storage conditions that saw them off. I have known a capillary action to take place between the pins and the glass button base with B7G/B9A valves and it only takes a few molecules of gas to upset the operating conditions of thermionic valves.
The Brimar 6AM6 is a very reliable valve and the special quality CV4014 is excellent.
I will attempt to write up what I hope to be the final chapter ASAP. Regards, John.
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Old 20th May 2015, 10:42 pm   #47
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Default Re: Murphy V114 9" table model 1947

Hi,
Back in the 1950's soon after the HMV 1807 came into being, we were advised by EMI to smoke the insides of the Z77 screening cans over a lighted candle to blacken the inside serface. because the reflected heat was causing early failure of the valves. It did seem to make them last longer.
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Old 21st May 2015, 12:05 am   #48
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Default Re: Murphy V114 9" table model 1947

In terms of dimensions the miniature EF91/6F12 is almost half the size of the Philips developed EF80 and yet the electrical characteristics are very similar. Also, the power dissipation of the two valves is similar.
Nevertheless, Murphy kept faith with 6F12 as the later models V120C and V108C employed the valve in the signal circuits.

Here's a list of the equivalents of the EF91: EF91,6AM6,8D3,Z77,CV138, Cossor SP6. Then there is the industrial and military versions of this valve to consider.

It might be possible that Mazda was the developer of the 6F12/6AM6.
http://www.aireradio.org/riviste_est...ola%20EF91.pdf

The writer acknowledges that the Murphy V114 was the first TV set to employ the 6F12.

DFWB.
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Old 21st May 2015, 7:12 am   #49
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Default Re: Murphy V114 9" table model 1947

That had never occured to me David. Of course the 6F12 was available in 1947 and maybe a year before. The EF91 did not appear in television receivers until 1949/50. The Ferguson 941T comes to mind and the later Bush TV20 series. The Etronic of around the same age has the Cossor version. Ediswan Mazda ahead yet again as they were in the 1930's. Pity about their post war.rectifiers..John
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Old 3rd Jun 2015, 8:25 am   #50
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Default Re: Murphy V114 9" table model 1947

Just to let you know that I will post up the final details of the V114 very soon. I have been very busy with my other interests and it's the longest day in less than three weeks!
Regards, John.
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Old 3rd Jun 2015, 8:41 am   #51
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Default Re: Murphy V114 9" table model 1947

Looking forward to reading the concluding results

Mark
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Old 3rd Jun 2015, 2:32 pm   #52
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Default Re: Murphy V114 9" table model 1947

Quote:
Originally Posted by Heatercathodeshort View Post
A hunt through the 'special condenser' boxes revealed a couple of NOS Dubiliar .1uf 7kv aluminium canned type, still in their original boxes. These have a Bakelite top and are very reliable. I cannot recall a failure regardless of age or storage conditions. Dubiliar, I believe an American based company certainly knew how to manufacture good capacitors.
There's a very brief history of the Dubilier Condensor Company here

http://en.wikipedia.org/wiki/Dubilier_Condenser_Company

Apparently the founder, William Dubilier, was responsible for the first use of a mica dielectric in capacitors.

John
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Old 5th Jun 2015, 10:15 am   #53
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Default Re: Murphy V114 9" table model 1947

At last there was a recognizable test card on the screen of the V114. Not by any means perfect but quite stable.
The display was very 'cogged' pointing to a defect in the sync separator. This eventually turned out to be a 20M leak in the line sync coupling capacitor C51 56pf.
Replacing this resulted in a much improved picture with stable line sync. Interlace is maintained over 90% of the frame hold control suggesting that Murphy Radio thought this necessary even with a 9" model.

It was time to sort out the rest of the wax paper capacitors. The sound was distorted and struggling to obtain full output. As expected the capacitors associated with the sound detector, interferance limiter audio preamplifier and output stages were all leaking, the best reading 1M. These were replaced [C39 .01uf, C41 .1uf, C38 .01uf, C42 .01uf C43 .02uf, C46 .005uf and C48 .01uf] This improved the sound considerably but it was still slightly distorted and considering the PEN45 4.5w output valve together with a large baffled speaker, was somewhat lacking in bass.

The distortion was cleaned up after replacement of the 4.7m resistor [R47] in the limiter circuit that tested as O/C on the AVO. The bass returned with a new 50uf cathode bypass electrolytic resulting in excellent sound quality similar to the Murphy A122 radio of the same era.

With small screen receivers I have always considered the sound quality to be a top priority. These early 9" receivers must have given their owners an immense amount of pleasure and with their excellent sound quality were much appeciated. Imagine the Coronation in 1953 with that fantastic music and the bright little picture. It would not have been the same with 'Alldry' portable sound quality, good as it was.

Picture and sound were now well up to specification. I feel that realignment of the two vision amplifiers would improve the definition slightly but the very large cores and Tuxite adjusters are stuck fast. They may have been adjusted for a slightly lower bandwidth resulting in much improved I.F.gain. This was necessary when every microvolt of signal was needed when originally operating from the tiny signal from Alexandra Palace.
It was not worth the risk especially as I have mislaid the telephone number of that lovely lady at Murphy service spares.

The chassis has been switched on for some hours with absolutely no problems or focus drift, quite a surprise with electromagnetic focus.
The UU8 main H.T. rectifier was a bit tired and took about two minutes to obtain full output, cured by it's replacement with a new Ediswan Mazda that was cradled within a huge decorative box.

Conversion to Band 3 was not routine. The RF amplifier 6F12, local oscillator 6L18 and the frequency changer double diode 6D2 were removed. The two cathodes of the 6D2 were joined together and the signal from the Murphy converter fed to this junction. The converter contained an aditional common [6F13] I.F. amplifier, presenting a decent signal to the vision and sound amplifiers and it's my guess that it was a very good performer on Band 3.

There were of course the usual slip ups when servicing the V114. A couple of wrong connections and a saga with the front end but detailing these would be boring and unlikely to be encountered with a similar model.

The chassis was all but finished and it would soon be time to slip it back into it's wooden shroud.

The final post will be a short summary of the V114 and a few off air pictures. Regards, John.
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Old 19th Aug 2015, 8:58 pm   #54
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Default Re: Murphy V114 9" table model 1947

How the weeks pass! It was the beginning of May when I started this project and I have just boxed it up after having obtained five 4.7M high voltage resistors for the EHT bleeder assembly the originals of which were all O/C.

Lining up is a bit of a fiddle with the V114. There is a certain amount of interaction between the scanning coils,the focus coil and the vertical drop down RF panel. The CRT and mask have to be dead square before sliding the chassis in. It weighs a TON.
If you set it up with the panel down it goes out slightly when the panel is restored to its working position. The adjustment screws are provided with holes to allow an adjustment tool to pass through but it is nasty and I fear a flash of an HT short if I'm not very carefull! I will continue to get it a little closer when I have some free time.

The picture really is very good and I guess it would have been much the same when new back in 1947. It has been well used and must have given a great deal of pleasure to it's original owner. I would add that the V114 was kept in good order by the excellent service work carried out by the local Murphy dealer in Northants where this little receiver was purchased. He certainly was a credit to Murphy Radio.
All the modifications recommended by Murphy were carried out including the change over from AP to SC in 1950.

The final pictures show the V114 working on channel 4. It was originally tuned to Alexandra Palace and must have struggled to produce a decent picture. It was originally working with a pre amplifier that is still mounted on the cabinet back.

This must have been one of the first television receivers to be installed in this very fringe area. Regards, John.
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Old 20th Aug 2015, 8:04 am   #55
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Default Re: Murphy V114 9" table model 1947

Right, clear the bench and get the HMV 1901 in!
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Old 20th Aug 2015, 8:38 am   #56
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Default Re: Murphy V114 9" table model 1947

Boxed up and back on!
Pictures show the RF/audio chassis dropped down in the servicing position. The back complete with channel 1 pre-amplifier and the tight fitting chassis in the normal position ready to go!
The entire front of the cabinet from the loudspeaker grill upwards can be removed for service access to the timebase valves and CRT which can be replaced without removing the chassis. Two sunken screws at the cabinet rear release it in moments, another quirk exclusive to Murphy with a table model. [The V310 was ten years away..]
Looks very military don't you think both externally and internally. Regards, John.

[PS I would need to remove the bench completely and demolish the bungalow to get the 1901 anywhere near a soldering iron Tim. It will happen...]
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Old 20th Aug 2015, 9:20 am   #57
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Default Re: Murphy V114 9" table model 1947

Lovely job John, looks better than they did in the '50s. Its a long time since I have worked on anything that old, as much an engineering job as an electronic one. I wish I had saved all the pre war sets we scrapped - still they wouldn't be worth anything if there were lots of them.

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Old 20th Aug 2015, 6:40 pm   #58
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Default Re: Murphy V114 9" table model 1947

Thanks Peter. I really enjoyed this one. When I was a very young lad I cannot remember seeing a V114 at the local jumble sales. Plenty of PYE, EKCO and FERGUSON 9" models but Murphy were very rare and far too heavy to carry home if there had been one.
It is a receiver I have wanted to play with for well over half a century!
I have carried out the 'repair' with just the required cleaning and replacement of the rubber wiring only where necessary. We all have our own ways of doing things but I think you can go too far, ruining the original construction and soldering carried out by those nimble Murphy assembly workers all those years ago. Regards, John.
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Old 20th Aug 2015, 9:50 pm   #59
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Default Re: Murphy V114 9" table model 1947

A wonderfull job.did you fully change the rubber cable or re sleeve were it is not that bad.i have always wanted to do a vintage television but have not got that brave yet
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Old 21st Aug 2015, 1:03 am   #60
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Default Re: Murphy V114 9" table model 1947

The successor to the V114, V116 and V118 was the V120C which was introduced in 1949. The most important change to the original 1947 circuit was the replacement of the mains derived EHT by a line flyback EHT system. Another innovation was the boost diode which provided a useful 40 volts negative which was supplied to the PEN46 cathode.
The double diode frequency changer was replaced by a Mazda 6C9 triode-heptode. Like the V114 the V120 employed the same type of 4 volt heater valves in the timebases. T41 thyratrons, DD41, PEN45 and PEN46.

I'll introduce my V120C in a new topic. The last time I switched the set on a bright raster appeared but no modulation.

A picture of my V120C was posted on #30.

DFWB.

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