This should finish up the LED light probe. I may have to do two posts because of the many pictures.
NOTE: Needed, though I haven't mentioned it yet, is something to insulate around the resistor, inside the tube. There is an electronic supply, commonly called "spaghetti" tubing. I'm showing a piece in the photographs. But a plastic soda straw would do as well. It needs to be the right size to fit OVER the resistor and slip INSIDE the brass tube. Also maybe some kind of boot for the back end of the tube to finish where the wire comes out. I didn't do this, but it might be nice.
Soldering Brass
Soldering will be just a little different, due to the brass tube's greater mass. It will take longer to heat up and to cool down. Soldering will take longer, almost like a slow-motion of the previous soldering. To avoid burned fingers, be sure to allow plenty of time for the tube to cool down.
A second factor is that metal conducts heat very well, There is much more mass than a wire, cross sectionally, and it is a foot in length. For every 2 or 3 degrees you put in with the soldering iron, the tube is probably dissipating away 1 degree into the air. So it takes longer to heat the metal.
Only two solder connections to the tube- one at each end. The one at the back will be easy. The LED end is a little more involved. The LED is physically attached to the tube by its negative (-) lead wire. The case serves as one of the conductors to the LED.
There are two ways I'll suggest to fasten the LED to the end of the brass tube. Any modifications to the brass tube should be done before putting the electronics inside it.
(Two LED mounting methods)
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If you decide to drill a small hole, try to make a tiny dent in the tube with some sharp object, and maybe very gentle tapping (very, very) with a hammer. This will help the drill get started without walking around. A Dremel can probably do it. Or a hand drill. A drill press would be ideal. The hole can be very small and brass is a soft metal. This is the method I chose. I think I used a #56 drill, but anything small will work.
(Tube With Small Hole)
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The second method of mounting I might suggest is making a little notch in the end to allow the LED wire to get to the outside of the tube for soldering. A small notch could be filed in the edge or perhaps even two careful snips with some good tin shears would do it. All you need is a notch the size of the wire diameter. This will allow the LED to seat against the end of the tube, while the wire passes through to the outside. (see diagram above) Keep the solder at least 1/4 inch from the end of the tube. This will make it easier to get loose, should you ever need to.
I'd do it the second way if I was doing it again. It might be a little easier, I think.
Final LED and resistor soldering
Cut both the wire leads on the resistor to about 3/8 inch. The resistor is, again, good practice dealing with short leads, because it deals with heat well.
NOTE: Small objects you are soldering will tend to stick to the tip.
Figure out some way to hold the resistor down. Lay something across it. Tape it down. Be creative. Anything that works is OK.
(Securing small parts)
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Tin the resistor, both ends, pretty much the way you did when the wires were longer.
Then, secure the LED with tape, after cutting the positive (+) lead to about 1/2 inch. Be sure you cut the right one. It is the longer wire, opposite side from the flat spot.
Tin the cut (+) lead of the LED as quickly as possible. Give it a minute to cool.
Finally, secure and tack together the (+) LED wire to one end of the resistor. It make no difference which direction the resistor goes. Again, try to be quick with the heat.
(Final LED and resistor)
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The negative LED lead needs to be shaped according to your method of mounting. (See LED Mounting Method illustration above) Bend it to the shape it needs now so that it fits nicely into the tube. It may take a little trial and error. Both methods will need a tinned solder spot either behind the hole or somewhere a short distance from the LED end. Make note for later where you want to tin the brass tube to allow soldering of the negative lead.
(continued in following post)