Murphy V310 LOPT rewind

[German Dalek]

Hi Steve,

Many thanks for your advice.
I don`t have this TV in question.
But Philips, Radiola/France, Radio Industrie/France and SABA did used cans with EY 51 valves.
I am not in the mood, to interchange them all the time, as time goes by.
Just because they are in oily soldered cans........

A friend of mine restored many cans and killed many.
His opinion was, that the transformers will be shot, when the air is not
vacuum pumped out of the can.
But it seems, that you have no problem with that.
Because of less high voltage?

Sealing must be possible with a good silicone adhesive.

I printed this thread out and translated it into german with
the clean pictures, because it will be worthful for the future.

Thanks again,
German Dalek

[murphyv310]

Incidentally.
British Relay bought dry LOPTs for the line (Murphy) sets, the TM4, M19/11 and others, not sure if the V310 was covered or any of the 405 line only ones. I've successfully replaced a V659 LOPT with a thorn 1400 Jellypot.

[Rich Woods]

Now that’s interesting. If you could PM me the connections that would be really useful.

[Niechcial,Steve]

I can't see that vacuum puping cans comes into anything. The leads are not through air tight seals, and the oil displaces the air. Moreover these cans are not made to be evacuated and would collapse under the air pressure!
Silicon sealant might work, but I am not sure how well it resists oil.

An amazing aside on product support on these sets. As you know, the original V310 used a self oscillating line output stage based on the the Mazda 30P4. Murphy quickly found this was not satisfactory because of line speed drift, so they added an extra osc valve. In the meantime Mazda selected particularly stable 30P4s from the production run, and labelled them '30P4MR' especially designed for use in the original V310. Presumably 'MR' stands for 'Murphy Radio'. In the 1972 Mazda data booklet the 30P4 is obsolete and replaced by the 30P19, but the 30P4MR was still available. The original V310 appeared early in 1957, so that is a product support of 15 years!

[murphyv310]

Hi.
British Relay service dept still had a few V310 sets coming in when I started in 1970 and in fact the reason I am Murphyv310 on many forums is because the V310 was the very first TV I had on my bench as an apprentice, it's always been my favourite 405 line set. I must have replaced hundreds of oil filled LOPTs, lids, lid hinges, Carousels, droppers, metal rectifiers etc. BRW rented 405 line only sets as pensioner rentals till 1974, mostly Murphy V310,410, 510 & 659, also Ekco T377 and T368 come to mind

[Niechcial,Steve]

Hi German Dalek. I think I have just understood what your friend is talking about. He is probably referiing to vacuum impregnation of transformers. This a process whereby a transformer is impregnated with a liquid varnish in vacuum conditions which are moisture free. When the varnish dries it effectively seals the transformer against any moisture ingress. The varnish has a much better dielectric resistance than air so it also helps to prevent insulation breakdown. It makes for a very reliable transformer, but it is something which requires commercial equipment and presumably you would have trouble finding someone to do small one-off jobs at a reasonable price. I don't think any tv transformers were made in this way until the 1980s. See https://cettechnology.com/vacuum-pre...0be%20improved.
The dielectric insulation resistance of pure oil is almost as good as vacuum impregnation. The trouble is that oil absorbs moisture from the air in cold humid environments such as sheds and lofts where old tvs are stored for many years. The water in the oil is not driven off by normal operating temperatures and results in poor performance or total breakdown of the coils. That is why it is essential to change the oil in these cans even if the transformer appears to be working ok. Having removed the old oil many restorers dry the transformer in an oven or by means of passing a heating current to drive out any moisture before r-filling with new oil.

[murphyv310]

Hi
A leak free with no seepage oil filled Murphy lopt shouldn't absorb moisture, if it can't get out the damp shouldn't get in. The problem arises when the seal is compromised or the transformer over filled when new, also the rubber top was supposed to be pinched together with forefinger and thumb when the vent hole was sealed with the little alloy plug, if not and oil expansion when warmed up it would compromise the integrity of the seal.

[Niechcial,Steve]

I agree Trevor, but from what I can see, by this age the seal is nearly always compromised. Then every time the set is put on its face to take the case out, some oil is lost. Mine certainly had signs of leakage
Meanwhile this set is running very stabley. I accidentally left it on for 8 hours the other day and the picture remained perfectly locked, linear and correct width/height. A brand new 30P12 I fitted went heater cathode short subsequently resulting in line and boost diode valves lighting up like light bulbs! Lucky that didn't happen during the 8 hour stint. All I need to finish the job is some channel 9 and 1 coils (3 and 11 fitted)

[Rich Woods]

Nice sets with a cracking picture, just never had much luck with the LOPTS back then which made them scrap in those days sadly.

[Niechcial,Steve]

Yes the frequency response is very good, and the gain very high. Did you scrap them all Rich?
I have made a new focus control to go over the tube neck as the original was missing. A plastic tube of the sort that 8 day church candles come in was ideal. I just cut it vdown to size and rivetted three little brackets to it

[Rich Woods]

Back in the 70’s? Sadly pretty much yes. My main sources were Radio Rentals & the local auction. I had a nice console version with sliding doors and 3 FM Radio wafers in the tuner that ran for a few years but then inevitably the LOPT failed & it went the way of all the others. Well done with the plastic tube by the way.

[Rich Woods]

The difference between then and now of course is that back then there was always another pile of interesting sets to have a go at the following week. Also as a teenager I didn’t really have the confidence, patience or skills to rewind a LOPT like so many others of us.

[David G4EBT]

As well as the Chinese basic hand-winder, which looks remarkable value for money, there is a rather more elaborate (and consequently considerably more expensive), winder which will traverse back and forth, and can be adjusted for wire gauge diameter so that the turns lay side-by-side. It uses the 'half-nut' system as used on Avo-Douglas winders to automatically change direction.

https://www.amazon.co.uk/9907308-Aut...08004362&psc=1

Followers of the 'Mend It Mark' channel may have seen two videos at the links below, but others might find them of interest.

Firstly, this video covers the modification he made to the machine. As it comes, the rod which accepts the coil former is about 9.5mm diameter (3/8"). Mark made another shaft to accept coil formers 6mm in diameter to enable him to wind some small 1mH chokes:

https://www.youtube.com/watch?v=WDkuQUTb8cE

This video shows the hand winding of the chokes:

https://www.youtube.com/watch?v=ZRlXEBUMTRs

Fine for solenoid type coils, chokes or transformers, which is what are perhaps most often required, but of course, the 'Holy Grail' are winders that can replicate wave-wound RF coils such as the likes of Denco, REP and Osmor. Almost all such 'DIY' type winders seem to wind coils in which the turns don't lay side-my-side so have a lot of air in them and consequently are large in size for a given inductance, like this one for instance:

https://www.youtube.com/watch?v=u21lEXzRwww

I've only ever seen one DIY machine where the turns are close-wound.

I've never seen another that can wide coils so narrow and the turns not collapse:

https://www.youtube.com/watch?v=tg67CvbcHaU

Not entirely relevant to this thread really, but of interest I hope.

[Niechcial,Steve]

Really interesting David. With the cheapo winder I used you basically ensure the closeness of turns manually, which is why it takes for ever to do. For multi turn fine wire coils (such as audio/frame transformer primaries), I think it would be very difficult to get close spaced even windings. But there again the inductance/capicitance is not so critical

[Ed_Dinning]

Hi Folks, note that for wavewinding it was usual to use enameled and silk covered wire, often run over some paraffin wax to help the coil build.

Ed

[Niechcial,Steve]

Yes the V310- uses that for the EHT overwind . I understand wave winding to be a dark art! Way beyond my ambitions.

[murphyv310]

Of course you could make a split diode type of overwind. They don't need as many turns.
Frank Cuffe made one a good few years ago with great success.

[Niechcial,Steve]

Certainly on the 310, a simple tripler works as well as the original overwind and gets rid of the hassle of the overwind altogether.

I have now managed to borrow some channel 1 and 9 coils and I'm going to try and replicate the osc. biscuits. I have tried my channel 3 and 11 rf biscuits with the 1 and 9 osc biscuits, and there is no significant loss of gain, so I will probably get away with just rewinding the oscillators.

[murphyv310]

Hi.
Between 2.2 & 4.7pf should pull in a CH3 coil to CH1 across the osc coil or even substitute the brass core for an iron dust core.

[Niechcial,Steve]

Thanks for that Trevor- I'll give it a go. Any ideas of values for channel 11 to channel 9?

Cheers,

Steve