Servicing The Murphys

By Trevor Goodenough
Forum Member: MurphyV310
Retired Radio & Television Engineer


Introduction

This article will give some additional tips and perhaps help for those wanting to fix up any Murphy from the V310 to the V759.

The V300 series was a radical design, it moved away from the “box” we all knew for so long, the shaped cabinet, the “sound Mirror” lid housing the controls and the lid itself being the switch, the presentation of the screen made the set compact and well received. For the engineer it was a two minute job to access the full chassis with the whole cabinet being able to be lifted off the chassis after removing two bolts.

1958 Range

The V310

: 17 inch, swing-screen console model

The V310 electrically was conventional bar two items, the tuner was made to a very high standard, it is virtually drift free and has no fine tuner, the base V310 has no AGC, it is direct line sync and initially had a self oscillating line output stage. The self oscillating line stage was trouble from day one, some mods were done initially with resistor value changes and tighter tolerance, the addition of specially selected 30P4’s did make a marginal improvement to the line drift it had, in fact Mazda marked these specially selected valves 30P4MR (MR= Murphy Radio) they were available for many years even after the improved 30P19 was available.

Murphy quickly got rid of the single valve line oscillator/output and well within 6 months the V310 had a 6/30L2 multi-vibrator fitted just behind the mains socket, this cured all the line drift issues. A kit was available from Murphy to modify the earlier sets, I very much doubt that the early sets survive now less the modification. It is a pig to do as there is very little access. During the V310 service life the set was reliable with many lasting longer than the 10 years expected, faults were decoupling caps in the IF stages, tubes (CRM172) and line transformers.

Line Output Transformers

The oil filled transformers on the V310 right through to the V759 all have similar issues. Firstly I’ll say categorically they should not leak, my V320A is totally dry and its the original transformer, if it leaks it is usually caused either by a faulty transformer, excessive oil in manufacture or contamination by coal fires or fags, this goes for the rubber seal. Faults on the transformer are, no EHT, if you have a healthy spark on the U26 top cap and no heaters it is caused by either the heater winding choke or resistor in the LOPT can going O/C, its as common as muck and was one of the biggest failures of the time, today its a 10 minute fix, just fit a TV20 EHT stick. Carefully solder a stout lead to the + end (red Band) of the stick and push the lead into the correct pin of the U26 base and put the top cap from the LOPT onto the the other end of the stick and off you go… fixed.

: Improvised lopt can
: Original Murphy Lopt

If you have a good picture when the set is cold but it gradually looses focus and the EHT & Boost drop after half an hour, the LOPT casing gets quite warm and begins to leak it is suffering with moisture contamination, I’ve opened them up before with quite a bit of water inside, this is usually caused by a bad seal on the transformer and after 50 odd years a lot of water can accumulate. These transformers come in two sizes one is the size of a Campbells Condensed soup  tin the other a Heinz beans tin size, yes Murphy must have used tins for trials back then. Open the can either by unpeening the can or cutting it at the lip. Clean it properly, get rid of the swarf and wash it in solvent, not too strong to to damage it, IPA can be used but remember it is hygroscopic and retains moisture, then let it dry, keep it at 60-70c for a couple of days or pass some current through the overwind so it gets warm 40c for a good few days. Rebuild the transformer in the correct tin for the LOPT diameter minding to put the poly sheeting from the old can in, experiment with the oil lever to just cover the top of the actual transformer and no more, use quality veg oil or transformer oil if you can get it not mineral oil as it goes for rubber.

Line Stage Tips

Building upon the above, here is some more info on the Line stage and what to do if the LOPT is truly duff.

The multi-vibrator line oscillator is reliable and drift free but after 50 odd years it is prudent to replace out of spec resistors, the cathode resistor is one to check and replace if out, it can cause the flyback time to be incorrect and will give a left hand foldover if well out, I always change this resistor with a quality modern component irrespective of its value. Also replace the screen feed resistors on the line output as a matter of course, this applies to all models from the 310 to 759 and the large screen variants. Ensure that the line drive coupling cap is replaced and the line output valve grid leak replaced too, a 470k risen to even 560k or more effects the shape of the drive waveform, its important to make sure the line output is properly driven with the correct amplitude and shape of the waveform.

If the LOPT has died whether due to damage, burn up etc there is two ways to go. You can if the overwind is the problem remove it and fit an EHT Multiplier to the 30P4 anode, it can be done in the LOPT can as well if you construct your own, it’s not my preferred method though. I have successfully fitted a Thorn Jellypot to a V659 using in the main the 1400 circuit with stabilised width and EHT, it works very well and even better with the Thorn scan coils, the advantage is these LOPT last and last, just be careful soldering to them. I see no reason why you cannot fit a Jellypot to a 310 or 410, on these lower defection power sets it is an idea to run the line output stage at a lower HT, this will reduce the scan power and also bring down the EHT to a level required for the smaller CRT’s.

Note: “I do have a V410 with a faulty LOPT here and I hope to fit a 1400 Jellypot in the near future and will by all means report back with my findings”.

Tuner

Regarding the the tuner unit, biscuits are hard to get hold of these days, after many years the oscillator core will be stuck fast so don’t be tempted to adjust the core until you’ve removed it from the turret and checked it is free to turn, if not a few drops of WD40 will soften up the hardened wax and you’ll be able to do any adjustments OK, the V310 needs a long plastic trimmer to do the adjustments and at one time a plastic knitting needle did the trick, now it seems you cant buy plastic needles so if you have one keep it and don’t loose it.

The V659 & V759 can suffer with height drift, in most cases this is a pain to sort out as it is caused by leakage in the paxolin board above the frame output transformer. It is prevalent on sets that have been exposed to damp conditions, the board contains the focus and linearity sliders and it can be clearly seen on a meter there is voltage on the actual paxolin, move the prof nearer the focus slider and the reading rises, yes it is this bad, the leakage gets worse the longer the set is on, on mine I made a new board out of one glass fibre laminate, drilled and pop riveted on solder tags, this effected a cure and I no longer had height drift.

A couple of thoughts to add

The rubber CRT surround in the barrel sets can disintegrate, it could be due to dampness or the suns rays, I’m not sure but I have been able to halt the issue by removing it and letting it soak in a hot bath of detergent and water for an hour or so, this completely stopped the issue worsening on a V530 and although my V320A was OK in this department it got the treatment 12 years ago and is still perfect. I have one less a mask due to this and would appreciate any comment on how to make a new mask or if anyone has one going spare, its for a V330 (same mask as a V310)

One good mod to do on the V430 or V530 is to remove the 441 ohm resistor for the radio heater dropper and fit a 4.5uf Motor run cap (Bypassed with a 100K) as the heat on the original resistor dropper damages the the EHT rectifier valve base.

Best Regards
Trevor


8 thoughts on “Servicing The Murphys

  1. Excellent advice Trevor.

    I must admit I wondered what the fuss was all about when folk mentioned this series of sets, that was until a Murphy V410 came my way. The V410 picture just blew me away, the best I had seen on 405 and as you point out, no fine tuner, remarkable. I have to say it was a pleasure to work on and a revelation in design both circuit wise and construction. I could stare at the chassis metal work for hours marvelling at the intricate form that nobody would even see.

    Attention to such detail sadly missing in many of today’s products.

  2. I was kind of brought up on Murphy’s, my apprenticeship was with British Relay and they had Murphy Astra sets for use on the line, also hundreds of off air sets from the then aging V310 right up to the V759. From 1970 to December 1974 was my most favourite time in the trade. They were a good company initially but the rot came in latterly.

  3. I’m going to add to this blog with some tips on how to fit an alternative line output transformer to this series of sets. The pressing one for me is the V410 which once warm the EHT tends to decay. In this instance the original LOPT is not leaking, so prior to fully condemning the LOPT I will do a series of tests and report back. Rather than have many pages I’ll do these tests, note down the results, take pictures and upload. I do feel the LOPT is rather ill but it’s never a good idea just to randomly point the finger, so I’ll outline the checks to be done prior to making a decision on the fate of the transformer.

    I do have an idea with these transformers that I’ve not done before. I still think a lot of the trouble with fading EHT is moisture and with it being oil filled can be a pig to remove. We know the boiling point of water is 100c (212f) so the properly remove moisture we need to raise the temperature of the transformer to 100c, this can cause all sorts of problems on tar covered transformers but in the case of the Murphy the transformer is encased in oil, think about a chip pan, the oil is around 150-200c and a wet potato splatters and pops when it hits the hot oil. Now I’m not suggesting to heat the LOPT to 150c or above but to get to 105c could well drive out the moisture and not damage (hopefully) the transformer. At this time I don’t know if the rubber or the insulating material would be damaged by 105c but if my V410 LOPT is at fault I really don’t to loose. I’d need to remove the alloy pin that is the level/filling plug and syphon out as much as 100ml of oil and leave the plug out to allow it to expand without damaging the seal and of course to allow any water vapour to escape, this is all in theory and as yet I don’t know if it will work or is a waste of time.
    So the next thing to do is all the relevant checks and go from there.

    I’ll come back to the blog in a few days time and add in what I have done and further info.

  4. Today I got some time with the V410 to confirm the LOPT was truly faulty, well that was my thoughts but in fact I am wrong. I now believe that a goodly number of Murphy LOPT’s may not actually be faulty. Of course there are the obvious faults like no U26 heaters or leaking oil but on a dry LOPT it isn’t always moisture ingress but another much simpler problem. I’ve already mentioned the 1k resistor on the cathode of the 6/30L2 it goes high value in time and gives the drive waveform the wrong shape, this resistor is used in all the “barrel” sets and the 659/759 multi-vibrator line oscillator. It causes line foldover on the LHS of the picture and a rise in line timebase current consumption. On the V410 it has a little circular paxolin tag board, it holds four resistors, (both anode loads, the cathode resistor and a feed to the line hold control) all of them are 10% tolerance. On my set the 1k had risen to 1.2k the anode loads of 22k & 100k had risen over 30% and 470k line hold control resistor to a spectacular 700k!!! It’s fiddly to fit these resistors but taking your time a good job can be achieved. On powering up the set it was noted that the line drive had risen by 20v P-P and was exactly the same shape as in the manual, width was increased, focus improved and HT up by just under 10v, a three hour run resulted in a much cooler LOPT, no de-focusing and less than 500v drop in EHT.
    The oscillator circuit is very similar in all models with just some component value differences, I think it is wise to replace the resistors in these oscillators, Murphy used 10% tolerance resistors and perhaps for good reason. I always replace the 0.01uf line coupling cap and the 30P4 grid leak on sight anyway and that stands.

  5. Hi.
    In addition to what I have already written I would like to add some tips on actually repairing the LOPT’s and what oil to use when refilling the can.
    It is virtually impossible to re-use the old can once you open it up. Being alloy un-peening its top part will inevitably cause ragged edges and cuts on the alloy. The best was is the use of a Heinz or Campbells tin, the Heinz Beans tin is the bigger size but Mr Murphy used both sizes for development work and both sizes are used in production, it’s uncanny that they are both the same. Don’t try and fit the LOPT into soup or beans as it wont go in!!! The biggest issue to do this is sealing the can so there is no leaks, oil is not easy to stop seepage. What I’ve found is the rubber insulation cuff/seal cant realistically be re-used, it will be contaminated with old oil and sealer, glue or whatever you have wont “stick”, so these days I bin the old rubber. Obviously you have removed the LOPT from the can for good reason, whether you have no U26 heaters or it was leaking or stored damp these problems should be confirmed as solved before refitting the LOPT into a can. Personally I’d remove the U26 heater winding and fit an external EHT rectifier stick or diode, it would be a shame to have another internal failure after rebuilding the transformer. The existing lead from the overwind can be retained. Dampness can be driven out by either cooking the bare LOPT in an oven (Fan assisted is by far the best) between 60-80c or by passing 10-20ma through the overwind, I prefer the oven method though. I have thought about heating the original can to 105c but as yet its just a thought. while the LOPT is stripped down check all connections and any that have put doubt in your mind then replace, or repair them.

    The selection of oil is another important thing, the oil needs to have a low thermal coefficient, you don’t want the oil to expand too much when warm, you also need a low hygroscopic oil so it doesnt absorb moisture and it MUSTN’T be mineral based. Olive oil is pretty good and the more refined the better, recently though I have tried DOT5 Brake fluid, it is silicone based, low expansion, and non hygroscopic, it doesn’t attack the LOPT in anyway and is by far the best oil to use. it is also not that much more expensive than premium olive oil. DO NOT use synthetic brake fluid (DOT 3, 4) ONLY DOT 5, use of the older types will ruin the LOPT as does Mineral based oils so no Duckhams Q20-50 please.

    A lid for the LOPT can can be made from a plastic lid from an aerosol, the idea is to take your tin can and measure it against an aerosol lid in a supermarket, that’s what I’ve done before, you get some strange looks though. keeping everything clean make suitable holes in the lid, fit grommets and feed the leads through them, also make a hole and poke a couple of inches of thin pipe through the hole, araldite it in place, this is for the vent, the original rubber was compressed in the factory once the can was filled through the filling tube and the alloy pin fitted to allow for expansion, we cant do that so the transformer needs to be vented, I’ve not had any issues this way but you can if you wish have a longer section of pipe and even fit a little filter onto its end. The use of a short pipe though is useful to allow a cocktail stick to be passed through as a dipstick or an extra hole could be made near the top edge of the lid purely for checking the level. The transformer should just and no more fully submerged in oil. I always araldite the aerosol lid to the can before filling it, use sufficient to give a solid join and seal, silicon sealer may do but I’ve never tried it, fill the oil via the vent pipe or dipstick hole, remember to measure the can for the required level and always refit the plastic insulating sheets before assembly. once filled fit a little rubber bung to and open holes in the lid and and make sure the grommets you use on the lid seal properly on the lid and leads.
    Have fun.

  6. One final point on transformer oil for these sets is that I got a chemist to identify the base oil used some years ago and it was confirmed as vegetable based. A mineral oil would have damaged the top seal very quickly from new apparently.

  7. As can be seen Murphy had used oil filled Line output transformers from the early 50’s and possibly beforehand. This is a picture from a V202 I restored a good few years back.

  8. Hi.
    It has come to my attention of another very good idea for the LOPT and how to contain it…… a Jam Jar. It certainly has advantages with being able to check the oil level and its condition with a quick glance and of course if the oil level increases with heat to an alarming level.
    The downsides of course are that can we have a jar of the correct dimensions? Will it require screening from the RFI from the LOPT? Plus of course any jam jar I have seen has a metal lid so it would need sufficient clearance from the top of the LOPT to obviate flashover, which is not a good idea in warm oil.
    The Douwe Egberts coffee jar is the right diameter. but not tall enough and with a narrow neck for the lid, I’ll research some jars and if I find something suitable Ill come back and do an update.

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