Found this old tube at the Shelby Hamfest. Seller stated it was used in a broadcast transmitter, and had exceeded the number of allotted hours. The silvering on the inside made it look better in my eyes!



Let's get started



Tools required to remove the tube base



The drilling operation



Hole saw used to put hole in bottom of tube. The drilling operation.

The completed hole. Leads soldered to Type 44 pilot lamp. No room for a socket inside the tube!



Type 44 pilot light inserted into the grid element inside the tube. It's a snug fit, bulb must be pushed in with

a small flat screwdriver. Since there are no other connections to the bulb, and the entire assembly is intended

to be mounted on an insulator, there is no reason to insulate the connections further. There is more than

adequate clearance between the leads so they won't short together.



Let's light 'er up!

Why?

Epilogue

I had been wanting a unique lamp for some time, and remembered seeing some for sale (I believe on eBay) several years ago that utilized a radio tube mounted on the base as a decorative accent. I took the concept one step further so that it could be used as a night light, or serve some other purpose where there is a need for a very dim light.First I had to choose what type of tube I wanted to use. The design of a transmitting triode, in my eyes, is a very elegant design. Nothing says "ham radio" like the dull red glow of a properly operating 3-500Z tube which is visible from the outside of an amplifier! Others may have their favorite tubes for this project, but for me, the 3-500Z was the perfect size, and could probably be had in "burned out" condition either free or cheap. After all, this project will ruin a good tube, so free or cheap is good in this case! The key element being that the glass envelope is intact, and the elements inside are pleasing to the eye. After a few inquiries looking for a candidate tube, I found none. I finally stumbled on one at the Shelby, NC hamfest. As it turns out, the box was labeled 5-500, but there are no markings on the tube. It "looks" like a 3-500Z. Close enough to work. And the price was right.The first thing to do after you have selected your tube is to find a location you can drill the glass envelope that will be hidden during operation. With a 3-500Z,there is a metal cup upside down in the bottom of the tube. It is welded to the electrodes which pass through the glass on the bottom of the tube, and these electrodes appear to be copper plated steel, i.e. nice and strong, providing lots of support for the elements inside the tube.I made a post in the forums here on eHam.net asking if anyone had ever drilled a 3-500Z before, and got all sorts of answers. "Don't do it- the glass is tempered and will shatter", and "keep it cool or the glass will crack". I even e-mailed Eimac, and the answer that I got from them was "I think it's tempered glass, but I don't really know". How kind and helpful! I didn't really get any answers from -anyone- telling me "I did it before, and this is how it's done". So I was left on my own to determine IF and HOW it could be accomplished. I don't mean this to insult anyone, I'm merely pointing out that I believe others probably have done this, and these people probably did not see my inquiry.Knowing that the usual carbide-tipped tile drill bit was pointy, I made the mental connection that it would force the glass outward as pressure was applied during drilling, and it probably would crack the envelope. What was required was some type of hole saw that would only apply pressure in one plane, i.e. inwards, not to any side. A trip to the local hardware store helped me locate a diamond-tipped hole saw.I knew that the glass had to remain cool during drilling from talking to a local glass shop. The only way I could do this at home was to drill the tube in a sink under running water, and run the drill at very low speed while doing it. Naturally, this precludes using an AC wall-outlet powered drill! I happen to own a battery powered variable speed cordless drill, and it was perfect for this application.First things first- there was a ceramic bottom on the exterior of the tube that held the pins in place. The pins on the bottom of the tube must be unsoldered and the ceramic base removed to get at the glass underneath it. A solder-sucker and a heavy-duty soldering gun is required. After all, you're not going to use the tube to transmit with ever again once you punch a hole in it, so don't worry about getting the pins overheated. Just get the solder out from around the pins as best you can. Once all the solder is removed, start pulling the ceramic base away from the tube while working the pins with the soldering iron. There may be a better way, but that's how I did it. Eventually it will give way and come off. It won't need to be soldered back on. You'll want to leave it loose so you can change the bulb you're going to put inside (if it ever burns out).Turning the water on, and running the drill very slowly, I began to drill in the center of the bottom of the tube in between the pins. There is a seal on the bottom of the tube where the factory closed off the glass after pulling a vacuum. I centered the hole on this little protrusion of glass. It went right up inside the hole saw. I let the drill operate a few dozen turns, then pulled it out and examined what progress occurred, if any. Sure enough, there was some white dust in a circle around the pin! The diamond-tipped hole saw was working! I proceeded to drill under the water, proceeding very slowly and methodically, wearing a heavy leather glove on the hand holding the tube (in case it broke), and stopping to rotate the tube about every 15 seconds to keep the hole concentric. The drill DID want to walk around a bit, but eventually created a track which held it in one place. You MUST drill VERY SLOWLY, and pause to rinse away the debris from drilling! The vacuum broke about 10 minutes into the process, which relieved me because that was one less factor to worry about. Obviously, because the tube was under running water, it sucked some water inside the tube. I continued to drill slowly and carefully under running water until the hole saw cut the plug from the tube. I rinsed the inside of the tube to remove any stray glass shards. Conventional thinking will lead you to believe that water will leave spots and residue inside. There is a trick to removing the water completely, which will not leave a chance for any spots to form.After making absolutely sure there is no remaining glass inside, give the tube three rinses, each with a couple of ounces of denatured alcohol (available from most paint stores). The water will bind with the alcohol, which will remove the water when poured out. Lastly, you'll need to VERY lightly blow dry the inside of the tube with compressed air to completely dry the alcohol. Look Ma, NO SPOTS!!! DO NOT USE A HAIR DRYER FOR THIS OPERATION!!!The heat COULD ignite the fumes from the alcohol!!! And do not use the full force of an air compressor, as it may damage the internal structures of the tube!Originally, I had planned to use LEDs to light the tube. I purchased one of the "grab bags" of LEDs from Radio Shack, as well as one each of all the others they had in stock. Some purported to be very bright. None matched the beautiful color of a radio tube's filament glow, but I did try them. I took some long forceps and removed some of the structure from the center of the tube, leaving a cavity inside the plate to place my bulb choices in. All LEDs failed miserably at being either bright enough or emitting a pleasing color of light. A red one looked pretty cool, but in the normal daylight coming in through the window, you couldn't tell it was on. In the pitch black dark of a closet, it did look great! But- that wouldn't accomplish what I wanted. I was looking for as much light as an ordinary night-light so it could be left on to light the way to the "water closet" at night. I happened to be working on another project, an antique Westinghouse radio, which used type 44 pilot lights. These bulbs are fairly bright, and operate from 6.3 volts AC. Of course, a bulb doesn't necessarily know the difference between AC and DC (technically, an AC bulb operated from DC will fail quicker by a few hours, but when you're talking about a 3000 hour bulb, 2995 hours isn't that much shorter!). And I won't get into the mechanics of why this is so, as it's beyond the scope of this article. The current draw on a type 44 bulb is pretty low, so it can be operated from many "wall-wart" type power supplies. And, the piece-de-resistance, the type 44 bulb fit PERFECTLY inside the grid element like it was made for it! And the color, brightness (when operated at 5VDC), are a near PERFECT SIMULATION of the tube being lit in use!I think radio tubes are beautiful. I want my grandkids to know about them. I want them to ask me questions so I can explain how they work, and why they're so much more aesthetically pleasing than some dumb ol' transistor. I want them to experience the same joy I did when sitting and listening to old radio programs as a teenager, like Jerry and Dodie on Radio Nederland. I want them to know the warm fuzzy feeling of curling up near an old tube radio, and the comfort of smelling the wax caps heating up, and coming to the realization that all is not evil in the world. The inevitable questions I will field the next time they come for a visit, and seeing them looking with wonder at this glowing glass bulb emanating it's warm ambiance will make it all worth it!Now I just need to build a nice decorative figured-hardwood base for it and install an ordinary lamp on top so it will have full function. The photos are not necessarily in order with the article text, but are in order of dis-assembly and re-assembly.