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Repairing the Tekna-Lite 2

The Tekna-Lite 2 was a waterproof camping torch taking 2 AA cells in a robust housing which screwed up to turn the light on. A whole camping generation bought them perhaps twenty years ago, and I am still getting e-mail from people wanting another one or looking for light bulbs that will fit.

The light bulb query is simple. The bulb is a normal MES (miniature Edison screw) and you can use either lens-ended or plain. Big electronics professional catalogue suppliers (RS Components is one multinational in this trade) have a wide range and an electronics service shop should be able to order a few for you. You need a voltage around two and a half Volts, and a current around 300 milliamps rather than the 500 milliamp bulbs that are easier to source.

William Filley has written in from Ohio to comment on bulb sourcing. I have not checked his data, since the innards of my Tekna appear slightly different to his, and Radio Shack (Tandy) part numbers may not be the same world-wide. he says :-

"Lamps for the Tekna can be gotten at Radio Shack. The part number is 272-1176. The only thing required is that the three tangs for holding the lamp should be very slightly pressed closer together."

When Stanley high-brightness LEDs appeared on the market, I designed an LED bulb for this torch that ran 30 hours on a battery set but threw a pretty dim light. The bulb never found commercial success, but mine has had heavy use for twenty years. I think I made the first LED camping torch, but true or not, they are certainly much more common now.

Recently the screw-on transparent end of the torch began to part company with its moulded-on thread, and catastrophic failure was not far away. This may well be a common trouble as these torches age. I was not prepared to farewell the Tekna so had to produce a repair to give me another twenty years or so of use. I established the transparent end was polycarbonate plastic, and the screwed section on it was glued inside a black collar also made from polycarbonate. This material is super-tough but attacked by many solvents, so all I had to do was find a fixing method which welded itself to the polycarbonate by solvent attack. I decided to fabricate a fibreglass reinforcing ring built round the black collar which also ran round the sides of the transparent end, firmly welding the thread inside the collar back onto the transparent end with a waterproof joint.

Modern fibreglassing is normally done with epoxy resin systems, but these resins will not dissolve polycarbonate, so there is very little adhesion between the two after setting. What I needed was a traditional polyester resin system used for fibreglassing, since the styrene monomer used in the formulation is an excellent solvent for polycarbonate. I bought the minimum quantity of polyester resin and MEK peroxide, which is the normal accelerator, plus a meter of one inch wide woven glass fibre laminating tape. If you are new to fibreglassing, read up and practise. I mixed up a thimbleful of resin with a drop or two of accelerator and used a few drops of this to stick down the end of about half a meter of the glass tape to the black collar and the side of the transparent end. An hour later this joint had set, anchoring one end of the tape. I reeled up the tape under tension so it formed a multi-layer ring round the torch end and collar, secured it with a rubber band, and put sticky tape over the very end where the light comes out to keep it free of resin, and also carefully taped over the threaded open end of the black collar to keep resin out of the thread.

I made up about an egg-cup full of resin, stirred in the accelerator and stippled the resin onto the glass fibre band using a piece of thick cardboard - no sense in wasting a brush. When the resin had been stippled in and the wet fibreglass laminate was almost free of air bubbles I snipped the rubber band, and kept stippling, always working to tighten the band rather than loosen it, until the resin got really tacky as it started to set so that it stopped the glass fibre length from unwinding. An hour in the warm was enough for the fibreglass ring to be 'green' or half-hard, and in this state I used a very coarse file to clean up the job a little. Two hours later I dabbed on a coat of automotive black acrylic to make things look more finished and the job was done. The Tekna-Lite 2 went back into service the morning after.

In the photo below the black paint covers the transparent end, apart from the light exit which is not visble in a side view. You can see the original diameter of the end start at the left, run in about 10 millimetres then widen as the new welded-on fibreglass band starts. The band finishes about 10 millimetres from the right-hand end of the black collar.

The O-ring seal that waterproofs the Tekna has not been worn by twenty years of use, but it does feel stiff as the threaded end is screwed over it. I used a little 'rubber grease', an automotive product for assembling and lubricating the rubber seals on hydraulic brake cylinders. Don't use a standard bearing grease or you may swell and destroy the O-ring. From the Castrol multinational the grease is GRR(B) but I do not know equivalents from other makers. With this grease in use the torch screws up smoothly, but the LED bulb is as dim as ever.

You are warned, with the appearance over the past year of affordable high-brightness white LEDs, the LED bulbs used in the Tekna as above are now pretty well obsolete. The project will not be straightforward, but for my own use, if not for others, I plainly want a means of inserting one of the new LEDs in the old Tekna housing.

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I will carry on now with the situation in mid-2007. If you want an old Tekna-Lite 2, hard luck. My previous source has none left. The good news is that Tek-Tite has decided to carry on the good work, and you can find all that is now Tekna torches, plus some nasty-looking knives, on www.tekna.us

Tek-Tite do hold replacement bulbs (globes) too. My white LED conversion for the old Tekna-Lite 2 I repaired was not the best thing I ever built. Tek-Tite sent me, for free, which is a first in this lifetime, their L222 white LED conversion lamp which drops into a later version Tekna-Lite 2 body. I had such a body handy, and dropped it in.

Doing a test on something like this is tricky. The LED came on, it had a beautiful beam pattern, and the new bulb holding arrangements were almost impossible to make flicker when turning the light on. Any flicker left is not Tek-Tite's fault by the way, unless you buy a new Tekna-Lite 2 from them, which you can. For the electronic there appears to be a minuscule ringing-choke charge-pump inside the bulb body, and this pushes the 1.5 or 3 volts from the battery source up to around 4 volts to drive the LED. It works best, like most of these, on 3 volts, but the low voltage capability means it goes on working until the batteries have almost expired.

I have used the system hard for nearly nine months. It works as it should, each and every time. What a bore. Only joking - this is a 100 per cent product.

If you want something tougher, you'll have to buy my burr-light, and I doubt very much that you will.