All-Tube Automatic LED Lamp/Night-light - Page 1
Forum section: electronics / projects

author: Cyberdragon
author_rank: Super Contributor
timestamp: August 19, 2016, 11:49:46 pm
content: You already know I'm nuts. Gone and done something really weird again...I made an LED lamp with a light sensor controlled entirely by valves. Well the circuit anyway, still need to solder it up, connect the transformer, and add a case of some sort. There are no transistors, the LEDs are driven directly by a valve, everything runs on 12V. It took me a very long time to figure out how to get the tubes to turn off in space-charge mode. (the circuit still acts up a bit, I'll have to see how it behaves once assembled) I originally intended it to be a night-light, but it's a bit bright unless I use a diffuser of some sort.Do you think that little transformer (on top of PSU) will be able to handle 300mA continuous (500mA startup surge) without getting hot?Parts List (minus power supply, any 12V power supply capable of at least 350ma will work):12AT7 (or 12AU7 or 12AV7)12BA67427 LDR tube (any LDR sensor will work but you might have to add some bias, you could also use other sensors or triggering devices)three 4.5v (20mA?) ultra-bright white LEDs (IDK what the max current output of this device is)1K 1/2W resistorLED current limit resistor (optional, depends on your LEDs and how hard you drive the input)500K Potentiometer (switch ganged or seperate)Trimmer Potentiometer (optional, to inrease max brightness/sesitivity)Tube socketsTube shield for 7-pin socket (12BA6 must be sheilded for thermal stability)You could use different LEDs with a different current resistor. Just keep in mind that space-charged electron tubes don't play around, they are totally capable of blowing up your LEDs (mine luckily survived 50mA through the tube with a 10ohm resistor).I'll draw up a schematic some time or other (probably in MS paint). I also note that the tubes respond to touching the wiring, so my next project could be a tube touch lamp.

author: technotronix
author_rank: Regular Contributor
timestamp: August 20, 2016, 07:42:14 am
content: I think it want handle 300mA without getting hot.BTW what happened? did you tried?

author: SeanB
author_rank: Super Contributor
timestamp: August 20, 2016, 11:53:16 am
content: Those little transformers only will handle 200mA pulsed, they run fine under 100mA. You can underrun the heaters in the valves though, and if you get a 9VAC or 6VAC one and run the heaters in series off that they will barely glow, but should have enough emission to work for your use. Bonus is the turn off will be easier, and they will be constant current switches.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: August 20, 2016, 12:22:59 pm
content: Strange, I would've thought a 60FX5 (or two, for more current capacity and no filament supply resistor!) would be enough. Phototube and an output, wired for hysteresis (schmitt trigger). Uhh, and something to invert it, maybe some screen-grid trickery?Also, isn't "all tube LED" contradictory?You could go with fluorescent or neon, instead. Fluos aren't so good at DC (reliability issue), so you might use some diodes (whether junction diodes count, is debatable; selenium and copper oxide rectifiers were standard for some time..) to hang a tube inside a FWB so it effectively controls AC.Or you can use a P-P transformer winding to control AC with a pair of DC-only devices. Or thyratrons, which has the advantage of controlling quite a bit of power from not much tube (a pair of 2D21s will do 100W easily).Tim

author: Ian.M
author_rank: Super Contributor
timestamp: August 20, 2016, 01:14:39 pm
content: In an alternate universe whereOleg Vladimirovich Losevdidn't starve to death in 1942 during the blockade of Leningrad, LEDs would probably have been used in period valve equipment.He was publishing research papers on point contact Silicon Carbide LEDs throughout the second half of the 1920's, and had come to the attention of international wireless magazines. If he'd survived and fled to the USA, blue SiC LEDs (and white by phosphor conversion) could have been commercialised 40 years earlier than their actual development by Cree in the late '80's.A schematic would be nice, but I certainly wouldn't want to use MSpaint! - Circuit Maker 6 Student edition (which can be found by googlingcircuit maker student edition zip site:.edu- hint 'Bobsclass') includes schematic symbols for vacuum diodes, triodes, tetrodes and pentode, and can simulate triodes and tetrodes.Sorry, no direct link - I don't want to give Dave any legal hassles as the 'Circuit Maker' brand name is now owned by AltiumOtherwise hand draw it on paper and scan it.You shouldn't have any real problems getting the 12BA6 to cut-off cleanly but you do need a negative grid bias. Assuming you are running its filament on 12.6V AC, as this isn't an audio application you can ground one side of the filament supply and run a voltage doubling rectifier from the other side tio give you a -35V bias supply. Another approach, as the control grid current is negligible, would be to level-shift the 12AT7 output through a grid bias battery - use three 12V A23 batteries in series for -36V of shift, which should be enough to get the 12BA6 into hard cut-off.

author: Cyberdragon
author_rank: Super Contributor
timestamp: August 20, 2016, 03:28:18 pm
content: Everything runs on 12V DC, no AC filaments or any seperate bias (bias is totally different and in some cases non-existant when running tubes in space-charge mode). Today I'll connect the transformer and monitor it with a thermocouple. The transformer is 10V RMS full-wave rectified by two diodes (plus a 470uF cap). Later on I might connect the tubes directly to the transformer so I can replace the silicon diodes with a 117Z6 (if tube diodes provide enough current at low voltage).Correct, I am using screen grid drive. The pentode drives the LED driver triode to positive grid. The pentode control grid goes straight to negative and the screen and suppressor go to positive through a 1K resistor. The second triode connects the first triode plate (on the LEDs) back to the screen and suppressor of the pentode. The light sensor drives the second triode grid positive turning it on and the pentode off to make the first triode grid float. It's not a phototube, it's a cadmium sulfide cell in a glass bulb, I could try a regular phototube though. The circuit does work properly, the only thing causing trouble is bad breadboard connections (once soldered it should be fine).I was going to use neon at first, but I don't have anything other than mini-bulbs or flicker-lamps. Both of which don't put out any considerable light. I wish I had some thyratrons, I keep neglecting to get some when I go to the tube radio club auctions. What about 807s to drive a 7W bulb instead? I also have a large deuterium arc bulb, but I don't have anything that has enough power to drive it (it takes like 500v at considerable current).I'll get that software to make a proper schematic then.

author: Ian.M
author_rank: Super Contributor
timestamp: August 20, 2016, 05:29:28 pm
content: Circuit Maker 6 can be a little flakey on a modern PC. It was released in 1998 for Windows 95/98 or NT 4.0, and uses DOS 8.3 filenames. Its help file requires the depreciated WinHlp32.exe to be properly installed. I run it under Windows XP with no problems.Also its 'File: Export: Circuit as Graphic' function is borked. Both Bitmap formats don't render the circuit properly and the WMF format export produces a malformed WMF file that many modern graphics packages don't support. It does have 'Edit: Copy to Clipboard: Circuit' which works OK and takes options from 'File: Export: Options...', so use that and paste it into your favourite graphics package.Here's a little sample for a 'starved' pentodeSolid state rectifiers have been around long enough for them to be 'period'. You could look for a suitable N.O.S. selenium rectifier, but they tend to go for silly money on EBAY, and are far too easy to 'cook' releasing toxic fumes. Unless you design for a higher +B, I don't think thermionic diode rectifiers would be practical.

author: Cyberdragon
author_rank: Super Contributor
timestamp: August 22, 2016, 05:13:20 am
content: I had it running for a little while and the transformer does get warm, but only about as much as a battery charger.The only problem now is a nice case, because hot melt glue and cardboard on a piece of an old jewelry box is looking like...well...hot melt glue and cardboard.Need to find something that looks good but is thin enough to mount tube sockets on (don't have any sheet metal or anything to cut it with). Is there such a thing as really thin plywood? I also found a broken tube to mount the LEDs inside.

author: Cyberdragon
author_rank: Super Contributor
timestamp: March 24, 2019, 07:39:05 pm
content: 3 Years later here's a shitty schematic (I'll have to find something better later). Necroed due to the "bizzare component uses" thread.There is another thread where I do a teardown to fix a bad(missing) solder joint (I'll have to find it).But to update, yes, the derpy device has been in continuous use for over 3 years (thought it's no longer left contuinuously powered and switched off remotely when not needed.)