Replacing the oil in a oil-filled lopty

[Mikey405]

Evenin' all.

A few weeks back I transferred a Philips 485U console TV from Solihull down the M5 to Devon. It was of course too tall to travel upright so I had to lie it on its front atop a selection of blankets and a duvet to keep it cosy.

All was well until I came to remove the set from the car the next day. The duvet was soaked with oil and on opening the doors covering the console's screen I discovered that the void between the CRT and the implosion glass was also swimming in oil.

The oil had leaked from the line output transformer leaving it all-but dry; something had to be done. "Simple", I thought - Just drill a hole and fill it back up. I expected the top of the transformer to be some kind of plastic or Bakelite but on closer inspection it turned out to be glass. After half an hour of very careful drilling with a standard HSS drill-bit it was becoming obvious that this particular kind of bit wasn't going to be any good. The bit was by now totally blunt and had hardly made any impression in the glass. A quick trip down the road to D&S Hardware Stores on Winkleigh airfield and I was the owner of a set of bathroom "glass and mirror" drills. The smallest of these new carbide-tipped drills worked like a dream. 10 minutes of very gentle drilling with my trusty hand-drill and I was through.

The next thing was to get the oil from the 500ml bottle into the tiny 3mm hole without spilling it everywhere. After a quick scout around I found the very thing: A filler-bottle with a tiny spout previously containing some foul-smelling concoction which people like to smoke in these new "vapour" thingamajigs. The nasty-smelling mixture was washed out carefully and the bottle thoroughly dried. A small amount of the oil (Shell "Diala B" transformer oil) was poured into the now-clean dispenser and the tiny spout re-attached. The oil was then very carefully drizzled through the tiny hole into the transformer.

After repeating this action about 20 times the transformer was full. The area surrounding the hole was cleaned scrupulously and a small blob of black silicone sealant was applied to seal everything up. I did consider using the silicone to try and seal the leaking rubber around the edge of the transformer but I strongly suspect that the whole thing would have looked a horrible black mess after I'd finished and I decided it really wouldn't have been worth the effort.

And so that was it. The oily implosion-screen, the CRT and the rubber mask were cleaned up and the set was put back together. I guess the same simple method could be used for any oil-filled lopty really; the two obvious makes being Murphy and Ekco.

The oil - Shell "Diala B" can be bought in industrial quantities from various places on the web if required but for more modest sizes, just do a search on eBay.

Thanks all.

From Mike.

[Argus25]

I once re-filled an oil filled lopty. I my case I kept well away from the top, and drilled a 1.5mm hole in the aluminium can base. I refilled it with oil scavenged from old Lucas ignition coils, I tapped the hole with a 2mm metric tap and sealed it with a flat head camera screw.
One thing when filling coils it is important to leave a small air bubble perhaps 8mm to 15mm diameter or similar. THere needs to be an elastic buffer (the bubble) to allow for expansion of the fluid (which is incompressible ) or it will be forced out the seals with heating ,but if the seals are leaking anyway it might not matter.

[1100 man]

Hi,
With all the aggravation which seems to be caused by wax or pitch insulation, I am beginning to see why some manufacturers thought it a better idea to use oil as an insulator. I assume it also tends to aid the cooling of the windings. I also imagine that these sets were designed to be transported upright: I'm sure the idea that the customer would lay the thing on its side and drive it hundreds of miles round the country would have been unthinkable with such an expensive piece of equipment!
All the best
Nick

[Peter.N.]

Job well done. I don't remember coming across Philips sets with oil filled transformers except the projection ones of course - unless I have forgotten, par for the course. Murphy's are the ones I remember as being the norm.

Peter

[Jac]

Well done Mike !

I still have to restore my 385U, which of course has the same chassis.
The whole chassis is greasy, so I suspect that it might be oil from the transformer.
Was it easy to see the oil level through the glass top? They should have provided a dipstick
Some oil filled transformers were vacuum filled (like the well known square cans) - I have no idea if that was the case with this type.
This type glass topped transformer was never used in the Netherlands (only the square metal cans in 8kV and 25kV versions).

Jac

[turretslug]

Well done on what must have been at times a somewhat nerve-racking and painstaking job- not to mention the "oh, " moment when the spillage was discovered! Fingers crossed that it's a successful and long-lived repair.

I wonder how close to its original value the 2.7 megohm (?) visible through the glass is!

That glass base with its flangeing and nipples is reminiscent of B8a/B8g/B9g type valve bases- perhaps they were made in a Philips valve plant? Any manufacturer must have been aware of the problems with "conventional" LOPTs re. insulation weakness, deterioration and breakdown, most would have shrugged their shoulders and said, "expected lifetime vs. production cost" but it would have been easier for the likes of Philips with in-house glassware handling to justify improved solutions.

[kalee20]

Sounds very Philipsey, quirky and different...

But refilling should give you a transformer as good as it ever was. Liquid insulation has many advantages, doesn't crack and let moisture in; doesn't break down and start tracking (or if it ever does, you just drain and replace); absence of hot-spots because it circulates...

Suddenly, I feel I must make an oil-filled jobbie sometime!

[mark pirate]

It must have been a bit worrying when drilling that hole, one slip and the windings would have been destroyed
I have yet to come across a glass topped LOPT, I think I would have removed the old seal and refilled it via the gap. Easy to reseal it with silicone.

Mark

[dseymo1]

Did you drill it 'dry', or, as is sometimes recommended, form a shallow oil-filled well around the position of the hole?

[Nymrod121]

Any health risks associated with the types of oil originally used in these transformers? (I'm thinking of polychlorinated biphenyl - PCB)
Best wishes
Guy

[matspar]

Interesting thread. I have had little experience of oil filled LOPTs only having owned one set with such a transformer. From memory this was a Philips/Mullard from around 1949. Possibly a 1502U? The lopt in this was a tall cylindrical thing similar to the one shown, and appeared leaky (had quite a coating of oil on itself and the surrounding chassis) the set always worked well however.

Would anyone care to explain a bit about the principle and construction of such a transformer? how were they wound? were oil filled Lopts more reliable than conventional ones and how does the oil insulate the windings? was the EHT rectifier always encased within the transformer? what are the survival rates?

Would be interesting to hear about first hand experiences/mods etc! and if any of us unfamiliar with the subject aquire a similar set!

A very happy Christmas to all

Matt

[kalee20]

Originally Posted by Nymrod121

Any health risks associated with the types of oil originally used in these transformers? (I'm thinking of polychlorinated biphenyl - PCB)

One would hope not - transformer oil is mineral oil, distilled to be 'dry' and having no ionic contaminants.

But PCB's could have been used! Popular from 1930's to 1960's, they also have the ideal properties for the application. It's just the environmental issues, the mutagenic properties, the carcinogenic hazards, which absolutely sucks for this class of compounds.

How would one know if the fluid is PCB in nature (assuming the transformer is not labelled)?

[turretslug]

I'd wondered this myself, having a few times encountered dribbling non-polarised uF-range capacitors. One idea for a very crude test I had (the environmentally-concerned and H + S inclined look away now....) was to take a saturating smear of the leaky substance concerned on some paper towel and attempt to light it (safe, outside, well-ventilated place obviously)- mineral- or vegetable-oil soaked paper is likely to burn enthusiastically, PCB-soaked not so (resistance to burning being one of their multitude of excellent properties).

It's not as if non-PCB oils are necessarily benign or harmless though- who knows what oxidation/reaction products could be present after several decades in other types of oils that long pre-date the likes of CoSHH, RoHS anyway. I can't help thinking that "if in doubt, don't" and minimizing handling in all circumstances is only wise.

[Nymrod121]

Re. PCBs

There's information given in a Wikipedia article that would seem to support turretslug's view as expressed in the closing paragraph in post #13:

"PCBs are technically attractive because of their inertness, which includes their resistance to combustion. Nonetheless, they can be effectively destroyed by Incineration at 1000 °C. When combusted at lower temperatures, they convert in part to more hazardous materials, including dibenzofurans and dibenzodioxins."

PCB is nasty stuff, irrespective of quantity - and if ever there was a case to be made in terms of 'assume nothing; check everything', I think it has to apply here.

I offer the following anecdote:

During the early '90s I was involved in a project to securely containerise a quantity of high-voltage capacitors that were believed to contain PCBs. They were removed from H.F. broadcast service under maintenance conditions that were definitely not routine and if anything were similar to those depicted in the 'Northmoor facility' scenes shown in 'Edge of Darkness' (Bob Peck et al) - white biochem suits, goggles, masks, minimum perimeter zones ... the lot. After placing the items in steel drums that were back-filled with sand, each drum was hermetically sealed then several drums were mechanically secured in steel boxes - each box also being hermetically sealed. The boxes were then welded to the floor of a series of steel 'bunds' (each having an overall volume of 2.5 times the total PCB liquid content, to allow for worst-case leakage). Seam welds were doubled-up (i.e. internally and externally) and each bund was tested by filling with water and leaving overnight on cardboard sheeting to give visible indication of any leakage. The next day, any faulty weld was remade and the test repeated (yes ... we found three in total). The entire consignment was subsequently shipped to Re-Chem in South Wales for disposal by high-temperature incineration as mentioned above.

I wonder if there's anybody on here that can add to this thread regarding the exact composition of oil used in these types of Line Output Transformer?

Best wishes
Guy

[Refugee]

That nuclear industry style disposal is well over the top.
Most of the material could easily have been distilled off and recycled before burning it.
The containment was well over the top.
I once read a story about some feral scrap metal dealers whom found some similar capacitors and broke them up.
The authorities complained a bit about the cost of cleaning up and the scrap dealers survived.
The stuff can't be that toxic that it must be welded into boxes surely.
I would have been satisfied with shipping them on a flat bed truck for specialist recycling.

[Heatercathodeshort]

Very well done Mike. Oil filled hermetically sealed transformers are generally far more reliable than conventional open types. The problem arises when the seal fails. Damp air is then absorbed into the oil and we end up with the same old saturation problem.

Philips, Ferguson [968T] are good are good examples but the seals appear to have failed in Murphy transformers during their service life.

I know of a couple of Murphy transformers that are performing very well with good quality cooking oil. Probably advisable to heat it to drive off any dampness before experimenting but if the correct oils can be obtained in small quantities as Mike discovered, that is the way to go. John.

[Jac]

concerning PCBs in canned transformers:
In the late 1980s I had the oil of a Philips square 25kV can tested, and the outcome was that it contained no PCBs or nitrite.
As far as I know, all these square cans have been manufactured in the Netherlands, so it is no guarantee for the oil in UK manufactured transformers, like the one in the 385U/485U family.

The attached document gives some info about identification of PCBs and materials containing PCBs. Not very helpful for the transformers with the glass top though...

Jac

[dseymo1]

Thanks for that paper, Jac.
It's interesting to note the comment that PCBs are not intentionally added to transformer oils, but may be present through cross-contamination of filling equipment. In the case of volume production items such as LOPTs, I suspect the risk is minimal.

[1100 man]

That sentence was only qualifying the fact that even if a transformer was not supposed to contain PCB's, it might well do so due to contamination!
As the bulk of PCB production was for dialectric fillings, transformers, even small ones, are very likely to contain them, especially from the '50s. If you look through the list, domestic capacitors used in motors, lighting, TV's etc are also a possible source of PCB's.
Like CFC's for refrigeration, PCB's had ideal properties and so were used extensively in all sorts of products, not just big industrial ones, before the risks were known.
It was interesting to note that a suggested test was to mix suspect oil with water. PCB oil would sink as it was denser than water, whereas mineral oil would float.
A very interesting paper and my conclusion from it was that it was perfectly possible (even likely) that the oil filled transformers and capacitors that we sometimes deal with might well contain PCB's.
Therefore taking proper precautions when dealing with such things is very wise!
All the best
Nick

[turretslug]

Yes- '50s US-made power-type capacitors in particular often feel somehow "heavy" relative to others, which makes me suspect that PCB filling is likely. I think that we develop an instinctive approximation as to "lightness" or "heaviness" relative to water SG (and similar density liquids, e.g. beer!) in containers, thus a jerrycan of petrol can feel oddly light even when brimmed. ISTR that PCBs, while spanning a range of specific gravities, typically centre aroiund 1.4.

I've often said that the devil doesn't just get the best music, but some of the best substances, too- PCBs, CFCs, asbestos, mercury, tetra-ethyl lead all have excellent properties in historic industry, they just happen to be rather bad for life in various ways!