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Old 2nd Nov 2018, 9:59 pm   #141
Radio_Dave
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Default Re: Help needed restoring a Murphy V310

Well I've done some Googling and it seems like vegetable oil, in this environmentally friendly world, is now being used as transformer oil. However I doubt that it's the same stuff that I buy in Tescos.
I don't want to wait for proper transformer oil to arrive so my new plan, unless somebody advises otherwise, is to re-use the old oil and use sunflower oil to top it up.

Regards
David
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Old 3rd Nov 2018, 10:10 am   #142
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Default Re: Help needed restoring a Murphy V310

No No No! The old oil will be contaminated with muck and moisture. Use new oil and dispose of the old stuff. Heat the new oil in a pan until very hot then let it cool before use. The can will need to be sealed air tight otherwise moisture will contaminate the new oil. John.
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Old 3rd Nov 2018, 10:13 am   #143
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Default Re: Help needed restoring a Murphy V310

I certainly wouldn’t re use the old oil, it’s contaminated and has obviously absorbed impurities over the years which could cause voltage breakdown.

I would go for sunflower oil, as mentioned by others. It would be a great shame to ruin all your efforts so far.


Good luck.

SimonT.


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Old 3rd Nov 2018, 11:42 am   #144
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Default Re: Help needed restoring a Murphy V310

This article suggest virgin yellow olive oil is the best for ageing http://iopscience.iop.org/article/10...6/183/1/012014

I am not sure if dielectric constant/losses will impact a LOPT performance but low losses sound like a good idea.
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Old 3rd Nov 2018, 10:00 pm   #145
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Default Re: Help needed restoring a Murphy V310

The very short shelf life of sunflower oil has put me off using it so I've ordered some proper transformer oil.

Regards
David
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Old 3rd Nov 2018, 10:28 pm   #146
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Default Re: Help needed restoring a Murphy V310

I'm sure that's the best way forward. I did some research on the 'net the other night and whilst various veg oils do have suitable properties, it depends very largely on how they are refined, what the exact make up of the oil is and what the water content is.
We don't have any control over this when just buying sunflower oil from the supermarket. For some strange reason, manufacturers don't put the dielectric constant in the nutritional information! We are not going to be able to hermetically seal the LOPT can so the veg oil will absorb water and also oxidise and therefore degrade.

I too will order some proper oil. I certainly didn't like the idea of reusing the old oil.

All the best
Nick
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Old 6th Nov 2018, 10:30 am   #147
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Default Re: Help needed restoring a Murphy V310

Just make 100% certain that the transformer oil you use is NOT mineral, if it is the transformer will be ruined in a few months.
Murphyv310 who used to be a member here has a lot of experience with these sets and has recently written an item on radios TV blog which I believe is very helpful.
Not sure how to link it here or if that is allowed.
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Old 6th Nov 2018, 11:46 am   #148
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Default Re: Help needed restoring a Murphy V310

Thanks for the warning. I'm no expert but isn't all transformer oil mineral based (as in petroleum based)?

There's a lot of confusion about which oil should be used in these transformers. I still plan to use Shell Diala, when it arrives, because I don't believe "ordinary" vegetable oil, at least without some sort of additives, would have been used.

I guess we'll find out soon enough if I've made the right choice .

Regards
David
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Old 6th Nov 2018, 12:13 pm   #149
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Default Re: Help needed restoring a Murphy V310

Hi.
I've just read his Blog and the suggestion is DOT 5 Silicon brake fluid, its low expansion and zero hygroscopic so it doesn't absorb moisture.

This the link. https://www.radios-tv.co.uk/servicing-the-murphys/
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Old 6th Nov 2018, 1:45 pm   #150
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Default Re: Help needed restoring a Murphy V310

Thanks for that very interesting and useful link but adding a third type of oil to my dilemma was the last thing I needed.

I still think I'll use transformer oil, mainly because it's because it's the only one where it's description fits the purpose I intend to use it for and (probably mainly) because it's just cost me £12 and buying anything else will cost me again.

Regards
David
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Old 6th Nov 2018, 1:56 pm   #151
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Default Re: Help needed restoring a Murphy V310

Throwing another spanner......

We had an appliance with an oil filled motor running in water. The numpties who messed with these unscrewed the filling plugs occasionally and poured out the oil. The makers told us to replace it with 3-in-1 oil, worked OK.

Could I raise my suggestion of a jam jar as a container again?
One with a metal screw top and fit a sealed insulated cable gland in it for the lead out?
Sam.
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Old 7th Nov 2018, 10:21 am   #152
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Default Re: Help needed restoring a Murphy V310

Hello.
Having conferred with Trevor last night he says the idea of a glass jam jar is probably the best solution as you can easily see inside the oil level, his only gripe would be the metal lid as it will be close to the overwind and could flashover.
On a personal note there is one make of Jam which alludes me at the moment that has a plastic lid.
I believe he is going to update his blog and a thread elsewhere with "Sam's" idea.
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Old 7th Nov 2018, 4:31 pm   #153
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Default Re: Help needed restoring a Murphy V310

All-glass jars of the Kilner or Mason type would avoid the risk of flashover, but would, of course, be more difficult in respect of the leadouts.
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Old 8th Nov 2018, 12:27 pm   #154
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Default Re: Help needed restoring a Murphy V310

I'm really a bit baffled why there is so much indecision about a suitable oil to re-fill vintage TV Loptys with.

There is really only one ideal oil in my opinion, it has excellent stability and many decades of longevity and it is dead easy and cheap as chips to get. It was developed by Lucas electrical industries for standard automotive ignition coils and has exceptionally good high voltage & dielectric properties.

Where do you get it ? From any used vintage Lucas ignition coils on ebay of course, just buy a couple of dirt cheap ones for a few quid (often one is enough) and cut open the canisters to retrieve the oil. I have used this oil in specialized high voltage probes at 55kV. I have also refilled a number of loptys with it.
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Old 9th Nov 2018, 2:10 pm   #155
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Default Re: Help needed restoring a Murphy V310

I would not use ignition coil oil as it probably contains pcb.
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Old 9th Nov 2018, 10:01 pm   #156
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Default Re: Help needed restoring a Murphy V310

Since dissecting my own oil filled LOPT, I have been aware of the potential for PCB's to be present in the oil.
Having read up about it on the internet, my conclusion was that any oil used in transformers, capacitors etc up to the mid 1970's, could contain PCB's.

Even oils that were not PCB based could contain PCB's due to contamination of processing & handling equipment.

I did a couple of basic tests on my own oil (density & flammability) and concluded that it was not wholly PCB based, but I had no way of telling if it contained traces of PCB without expert analysis. So I felt minimising skin contact was a good idea so have used gloves in my handling of the transformer internals.

I feel ignition coil oil would carry the same level of risk so whilst its' properties are ideal, I'm not sure it would be my first choice.

All the best
Nick
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Old 9th Nov 2018, 10:09 pm   #157
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Default Re: Help needed restoring a Murphy V310

I was hoping to get the LOPTx back in today but I ran out of time. It's going to have to wait until next week now.

Thought I might as well update you though. The LOPTx was refitted into the original can and I used a piece of garden strimmer line to act as a form to help me roll the top over. I think the seal was good, well as good as it was before I started, but as I already had a tube of neutral silicone I ran a bead around the top as well

The Tx was refilled with Shell Diala B, which is a mineral based oil but it's been in there for three days now and so far I can't see any deterioration to the rubber seal. Hopefully it'll be OK. I found it difficult to measure the how much oil was in there with a cocktail stick so I overfilled it and then used a syringe, inserted to the required depth to draw out the excess until air was drawn. I'm not sure how much should be in there but I chose to fill it to the line shown in the last picture, which I think should be around half way between the top of the winding and bottom of the seal.

Regards
David
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Old 9th Nov 2018, 10:33 pm   #158
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Default Re: Help needed restoring a Murphy V310

Hi Dave,
That all seems very reasonable to me! Neat trick with the syringe! That hard ring around the top gives an ideal support for a bead of sealer.

Is your top rubber seal hard or soft? Mine was still very flexible, but the PVC wiring has gone rock hard and won't seal properly where it goes through the 'boots' in the rubber top.

I read the article by 'Murphy310' which was very interesting. I must confess I could not see any need to replace the existing can with a baked bean tin, ingenious though this might be! I'm sure your method will work fine.

I imagine the worst that will happen, with the Diala oil (if indeed anything happens at all), is that over time the PVC wiring and rubber seal will go hard. I don't think it is likely to damage any materials used within the transformer itself- certainly there are no plastics in my one.

I was interested in the idea of using silicone brake fluid. This does have some ideal properties- it's lack of water absorption being one of them. Of course it would need to be able to mix with the residue of the original oil which will still be in the windings.

Cheers
Nick
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Old 9th Nov 2018, 11:02 pm   #159
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Default Re: Help needed restoring a Murphy V310

Quote:
Originally Posted by 1100 man View Post
Is your top rubber seal hard or soft? Mine was still very flexible, but the PVC wiring has gone rock hard and won't seal properly where it goes through the 'boots' in the rubber top.
Yes mine is exactly as you describe yours.

I think the fear is that mineral oils can attack and dissolve natural rubber but I have a feeling the rubber seal on these LOPTs are some sort of synthetic rubber, like neoprene, which should be ok (hopefully!).

I'm actually testing some pieces of rubber insulation, stripped from some old hook up wire, in the new and old oil. It's only been a few days but the rubber seems to be softening and swelling in both of them.

Regards
David
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Old 15th Nov 2018, 4:18 pm   #160
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Default Re: Help needed restoring a Murphy V310

The LOPTx is back in and although I didn't feel brave enough to use the HV probe today I'm sure I've found the missing 1kV to get the EHT up to the specified 15.

The ion trap has been adjusted again and now seems to be back in the position it was originally. I can focus the picture with the focus control in the correct position and in the middle of it's travel. I've ran it for 40 minutes and there's been no shrinking or collapse of the picture. When I felt the LOPTx and it was barely warm.

I still have a problem when I advance the contrast into the last 1/4 turn of it's travel. Something starts ticking/arcing accompanied with the top inch of the picture twitching to the right. I would really appreciate and suggestions what could be causing this?

There's always been a suspicion that tube is a bit duff and I may need to rejuvenate it. I've no idea how to judge this so I've attached a couple of photos which I hope I can get some experienced thoughts on

Regards
David
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