My dad gave me an old lamp he'd made out of a radar tube off of an EC-121's RADAR set. His lamp was only the tube mounted to a base with a little lamp socket pushed up into the tube. (Note - the tube is still integral - the glass hasn't broken, as far as I can tell.) He mentioned in passing last night, however, that he wished he'd gotten his electrician to show him how to "...wire it up to glow blue," when he made it. Apparently, GI's in Vietnam lucked up on these discarded vacuum tubes and wired them so that the heater grid (I'm guessing at that - I don't even know if that's the right term or not.) would glow bright blue when 120 VAC was applied across two contacts on the tube. I tried to scope it out with a multimeter, but no luck so far. Does anyone have any experience with this, and can you tell me where to solder my connections to get this effect?
2007-03-04 11:30:49 · 2 answers · asked by snapz007 2 in Science & Mathematics ➔ Engineering
Great minds - thanks to both answerers below. I couldn't get continuity across anything inside the tube, so I just finished re-drilling and installing some blue LED's. Thanks a million!
2007-03-04 14:47:32 · update #1
You are looking for the heater ("filament"). However it most likely was not made to take 120 volts, probably 12 or 24 volts instead. If you found the heater connections and put 120 volts across it there would be one flash of light lasting for a fraction of a second until the filament burned through from the excessive current. It is like what would happen if you tried to run a car headlight on your house voltage.
If you have an multimeter (or could borrow one), put it on the ohms function and then clip a probe onto one pin. Then touch each pin in turn with the other probe. When the meter shows a connection (reads something other than "open circuit") you have found the other end of the filament. If none of them connect with one then clip the probe onto the next pin and try the others in sequence. Again a reading is good. If not clip onto the third pin and repeat. Keep doing that until you find a pair with a connection. If you were carefully to not skip any and have not found a connection, then the filament is already burnt out and it is not going to light up ever.
That "bright blue" seems kind of odd to me. The filament usually comes on yellow or red and is more heat than light coming from it. Maybe what they did is get an arc to jump between two electrodes in the tube. That would be blue. However an arc is a short circuit and would blow the house fuse if you just connected the tube to 120 Volts. You would need to put a current limiting component in series (like a 4.7K ohm 1 Watt resistor) to keep fuses from blowing. You could try that with any two electrodes that are not connected with each other. Be careful not to kill yourself while messing with that lethal 120 volts.
2007-03-04 11:54:09 · answer #1 · answered by Rich Z 7 · 0⤊ 0⤋
The tube should have a part number on it. Try doing a search on the part number to find the pin out. You may also get other information in regards to what voltages the filament etc were operating at.
The tube may have lost it vacuum and may not work either. But it is worth experimenting with if you want. Radar tubes usually run at very high voltage so be careful. 110Vac will kill you.
Blue LEDs are pretty cool too. LEDs are low voltage (easy to experiment with) and high brightness ones put out a lot of light.
2007-03-04 13:46:00 · answer #2 · answered by Lost in PA 2 · 0⤊ 0⤋