Screen magnifiers - 40s/50s TVs
 

I have a Pye B16T and have just acquired a D16T. Both are fitted with liquid filled magnifiers of the familiar kind. Both magnifiers have lost some fluid through leakage from the filler hole, and I need to top them up. When I was a schoolboy solder-monkey in a TV repair shop in the late fifties, I seem to rember being told that they were filled with Liquid Paraffin (the kind used as a laxative)!

Can anybody please confirm this? The last thing I want to do is use an incompatible fluid, let alone anything which would attack the Perspex(?) casing.

Re: Screen magnifiers - 40s/50s TVs
 

Yep - liquid paraffin (not paraffin wax).
Will take a bit of explaining if you are getting some from the pharmacist to refill it!

I have heard mention of glycerine, as well.

A little taste should confirm, but don't swallow it, just in case.

Liquid paraffin is very greasy with little taste. Glycerine has a strange hot but sweet taste.

Re: Screen magnifiers - 40s/50s TVs
 

Mike Phelan:
The few magnifiers I've met before were filled with liquid paraffin - I've not heard before of glycerine (glycerol) being used in this application - interesting.

Take care with glycerine. It's actually very hygroscopic in its pure form (hence, possibly, the strange, hot taste as your tongue dehydrates...) so if used in a magnifier would need to be properly sealed to prevent exposure to the air (and leakage, of course).

Try taking a small sample of the liquid, and mixing with water. Glycerine is highly soluble, but liquid paraffin isn't - it will float on top of the water.

Liquid paraffin is odourless, but is alleged to smell slightly oily if you warm it up. But take care - liquid paraffin is (potentially) flammable - I don't think glycerine is.

When you've decided on a replacement liquid, mix a small sample of it with a sample of the original liquid - I don't think Liquid Paraffin and Glycerine are miscible, so if they don't mix, you've made the wrong choice. Then try a small sample of the replacement on a non-exposed part of the plastic case where it won't be seen, and check for any adverse reaction. Liquid paraffin is fairly non-reactive with most things, probably why it was used in the first place. If you can get enough of the replacement liquid, I would recommend replacing the entire contents of the magnifier rather than just topping-up the existing fluid. Mixing old and new might result in slight cloudiness.

Re: Screen magnifiers - 40s/50s TVs
 

Thanks for that, everybody. Re. yellowing, both mine are yellowish, but I thought it must be the plastic that had discoloured, not the fluid. I'll draw some out and see if I can tell.

I suppose the magnifying effect is due to the refractive index of the fluid, not the shape of the container. Would glycerol have a similar index to liquid paraffin? Or doesn't it matter much?

Dave

Re: Screen magnifiers - 40s/50s TVs
 

ISTR that my comment about glycerine was something I spotted in a book or magazine years ago.

If glycerine was used and had a different refractive index, presumably the convexity of the front would need to be different as well.

I don't think it is flammable, but I do know that if you drip it on sugar, it will start to smoulder and burn. Do the same with potassium permanganate and it will burst into flames!

Now, putting the Useless Facts and Weird Tests section away for now, I would have thought it more likely that the yellowing is caused by sunlight on the plastic, not the liquid itself.

Re: Screen magnifiers - 40s/50s TVs
 

Mike Phelan:
Well, the refractive indices probably will be different: and the effect will be to alter the focal length of the lens, of course. Therefore the 'magnification' will change: though whether by enough to be noticeable is debatable.

You can always increase the magnification by increasing the lens/set distance: my old granpappy was a woodwork whiz who soon knocked up a plywood frame to hold the lens at a fixed distance from the screen (formerly the thing dangled on the set-front by canvas straps passed over the set-top and knotted round the 'bowler-hat' extension at the rear). This had the desired effect of increasing the magnification: it also drastically reduced the viewing angle and picture brightness, so the whole family ended up huddled together in the darkness.

And again, that's very likely the case. Remember also that these gizmos are now of the order of sixty years old or so - the plastic will almost certainly have become quite brittle due to migration of the plasticisers (possibly into the paraffin..). So handle with care: if you don't have a filling-plug already fitted, you'll need to take extra care in drilling one 'cos it will be very easy to start up cracks in the plastic which may well finish the product. Which would be a pity: I wonder how many of these articles have survived to the present day (and OT, if I may be permitted for a moment: how many of those stick-on 'convert your TV to colour' rip-offs that one saw in the adverts in those days..)

Re: Screen magnifiers - 40s/50s TVs
 

We are close to the bottom of this now. I drew off about 50ml of the fluid, which could be seen to have a distinct yellow tint. I soaked a piece of paper in it and lit it. It burned with a yellow smokey flame. Bad move! - right under the workshop smoke detector (linked to the others in the house), causing great agigtation in the other resident. :dunce: The fluid is not miscible with water and is tasteless (I did this 2 hours ago, so probably not poisonous either). Conclusion: may very well be liquid paraffin.

The flat back part of the lens extends into a flange around the unit. This part of the Perspex is perfectly clear, so I assume the rest is likewise.

Tomorrow I will add a small amount of Liquid Paraffin BP to one of the magnifiers and see if it mixes. If so, I'm going to drain it and refill completely. I don't know how much I'll need - hope this stuff is not too expensive!

Empirically,

Dave

Update: I've now drained some more of the fluid and can see that the main part of the lens is also clear.

Re: Screen magnifiers - 40s/50s TVs
 

Presumably, you could drain off the existing contents into a measuring container.

Re: Screen magnifiers - 40s/50s TVs
 

Liquid Paraffin is also known as nujol ??? and several other names:-

http://ptcl.chem.ox.ac.uk/MSDS/NU/nujol.html

Don't try this at home! :-

http://i15.photobucket.com/albums/a3...heoptimist.jpg

(From Radio Constructor, March 1953 ;D )

Regards, Mick.

Re: Screen magnifiers - 40s/50s TVs
 

OK, solved it. Liquid paraffin is listed in the British Pharmacopea and is available off the shelf at my local pharmacy in 150ml bottles. The pharmacist can also supply a 2 litre size for about £10.00, 25 litres available too.

My grateful thanks to all who have added their illuminating contributions to this discussion.

Magnificently,

Dave