The LED will be vertical and its wires will be arranged as in this drawing. By experience, at least for those I have, it will be better to place the cathode (the minus sign) upwards; thus, the luminous point will be centred at best and perfectly simulate an incandescent lamp.
Note: in the drawing, the wire colours are purely fictitious, since they are varnished wires. There are nevertheless enamelled wire of different colours, which could prove very convenient.
For soldering operation, it is necessary to correctly maintain the LED, which is even more delicate than for the “glass”. I prepare a waste epoxy plate by milling a groove, 1 mm wide and 0.2 to 0.3 mm deep. On either side of this groove, about 1 mm from the axis, I drill two ø 0.4 holes. Other V-grooves, approximately 0.1 mm deep, made with a PCB engraving bit, are used to guide the connection wires. The plate is placed in a vice, the LED is placed in the groove and held by a ø 0.3 galvanized iron wire passing through the holes and folded under the plate. I have checked that this wire does not take the solder, even if it is coated with flux.
Once the LED is firmly seated in the groove (head down), I wash it with Bergeon flux. I approach the slightly tinned tip of the iron to transfer a minimum of tin on the soldering pads of the LED.
I use a very fine (ø 0.1) varnished wire. It is cut into pieces of about 100 mm. The simplest stripping is by varnish carbonization. To do this, I set my soldering iron to the highest temperature, 400 °C, and I let a drop of tin melt on the tip. I plunge the wire end into the tin, which has the effect of both stripping and tinning it. Attention: with other types of varnish, probably more resistant to heat, this method doesn’t work, and it is necessary to scrape with scalpel or abrasive paper, which is very painful…
A wire is brought into position, held by spring clamps (see photo above). Caution: if the tinned length is too long, allow it to protrude from the free side so that it can be cut away once the soldering is made. As the wires are going to be bent to get out of the same side, bare parts should not touch each other. It remains to pass the iron, with no additional tinning.
For each welded wire, I pull very lightly to test the solder quality, then I colour it with a felt pen, black for the cathode (–), red for the anode (+).
If you wish to twist the wires, this is now the time to do so: the breakage of a wire will be less calamitous than after installation in the lamp. Do it with the utmost delicacy! But this will facilitate the future wiring of the lamp.
Once the two wires have been soldered, the LED must be soaked into preferably warm water. Indeed, the Bergeon flux is both acid (despite the manufacturer’s assertions, it is enough to have once on the lips: characteristic taste) and electricity conductive. If you test the operation before this cleaning, there is a risk of some surprises!
After soaking and drying, it is possible to test with a diode tester, according to the method described here. Moreover, subsequently, it would be good to keep the LED powered. On the one hand, this makes it possible to be immediately warned if by misfortune a wire breaks, and, on the other hand, the LED position inside the lamp will be seen much better. The tester can be replaced by a small wiring on a test plate, with a 10 kΩ series resistance, and powered with a 12 V DC supply.
At this stage, the exterior of the lamp may be painted with Humbrol aluminium grey no.56 in two or even three layers because of the transparency of the material, as already mentioned. But these layers of paint have the disadvantage of making details less visible. Attention: if the lamp is to be glued from the back, you should remove the original paint, which holds very badly.
The lamp, without its “glass”, is fixed in the vice equipped with its rubber jaws, face up. The LED is inserted from the front, the wires first. They come out through the base, and you have just to pull them gently until the LED goes into the case. It is sometimes necessary to insist gently but firmly so that it is set correctly, pressing it with a wooden cocktail pick for example. Here, the fact that the LED is lit makes its positioning much easier, because it tends to get the wrong way. Once the correct position is found, I immobilize the wires with some adhesive tape.
I put a small drop of no-solvent Pattex 100% glue by the opening of the lamp. No Kristal Klear or wood glue, because the water it contains can oxidize copper and short the LED! In general, it does not last, but it’s a bit stressful!
Then let’s replace the “glass”, always stuck to its piece of adhesive. It is necessary to engage it delicately by checking that it doesn’t get crooked. As soon as it is properly aligned, it can be pushed into completely, which has the effect of trapping the LED and driving a part of the glue towards the base.
If the LED is still lit, a sign that everything is OK (!), it is only necessary to disconnect the lamp and place it into a small clamp, always face up, waiting for the glue to dry.
The next day, I place a tiny ball of Patafix in the base. Two reasons: softly hold the wires, and prevent light leaks downward.
And test again. No, I’m not paranoid.
0.15 mm enamelled wire reel
7 different colours
€5.90 for 50 m — price 2017
at fohrmann-WERKZEUGE GmbH