Using Vacuum Tubes As Immersion Heaters

Fellow Hackaday writer [Ethan Zonca] was doing a little bit of woodworking recently and decided to test ammonia fuming on a small piece of oak. Yes, this means discoloring wood with ammonia vapor, and it’s a real technique. [Ethan] wanted to increase the rate of evaporation of his ammonia solution and decided to make an immersion heater. Out of a vacuum tube.

This is a non-optimal solution to the problem of heating a solution of ammonia – already a bad idea unless you have a fume hood – but it gets better. The vacuum tube was slightly cracked, something easily fixed with a bit of silicone sealant. This was then immersed in an ammonia solution, wired up to a driver board and controlled by a homebrew PID controller. If it’s stupid and it works, it’s not stupid.

After getting the ammonia solution up to 30° C, a noxious cloud of ammonia seeped into a piece of oak. This was left overnight, and the result is something that looks like old barn wood, and looks great after some linseed oil is rubbed into it. This is only a test run for fuming an entire desktop this spring, and while that’s a project that will require a real heater (and doing it outside), it’s still a great demonstration of lateral thinking and great woodworking techniques.

22 thoughts on “Using Vacuum Tubes As Immersion Heaters

  1. Using a “slightly cracked” vacuum tube to heat ammonia seems to be an idea that itself is slightly cracked. Surprising that even with gobbing it up with silicone that the tube heater didn’t burn out right away.

    1. Agreed use a god damn vacuum chamber.

      This should work, obviously test the materials for problems in ammonia vapor.
      Get a vacuum pump seal up the desk surface you want to fume with vaccum bagging. Wet some rags with ammonia then place them with a barrier inside the vacuum bag. Seperate the surface with peel ply and enough other rags to absorb excess liquid… vacuum to 20 inches of mercury. Stay below 26 inches and the water should keep from vaporizing readily. Ammonia will boil off and saturate the very small area left in the bag. Vacuum will reduce as it vaporizes but leave it to equalize.

  2. Ummm … the heater in a valve/tube is mostly surrounded by vacuum – about the worst way to transfer heat. Therefore, the whole concept makes as much sense as filling a Thermos bottle with hot water an then trying to immerse it in a substance you want to heat up… yes, tubes DO get hot but I would probably try a peltier element and a petri dish…

  3. This reminds me of another unusual heating/cooling story involving vacuum tubes. A million years ago, in the early 60s, amateur radio operators used to delight in making transmitters using a type of vacuum tube called a 6L6. It was rated at about 30 watts output, and, hams being hams, they liked to see how far they could push them. One fellow reported in QST (a journal for amateur radio ops) that he managed to get 100 watts out of the metal cased version of the 6L6 for a brief while by freezing it into a block of ice for cooling. He reported that it worked fine for 20 minutes or so, until the ice melted.

    1. Quote from regarding the metal-cased 6L6:

      “I haven’t tried it, but you can operate 6L6′s upside-down in Ethylene glycol bath at a plate dissipation considerably above the 19 watt maximum called out in the specifications. Do not do attempt this if you have small children, pets, or a fussy spouse at home.”

    2. My uncle was into ham radio and he had a linear amp in the trunk of his Studebaker and he could only run the linear when the engine was running. I watched the heat from the amp melt the snow off his trunk lid one January afternoon. The snow melted off the trunk faster than it melted off the hood!

  4. yes, it is only stupid idea, but mostly because it required a lot of effort and is not ideal in any way. A standard water heater core from a water heater would do a better job, and it would be longer and have more surface area to produce a more uniform vapor. The controller would be easier too.

    The tube, if you continue to use it, should be coated in silicone so it does not break while in the ammonia, and cause some unforeseen disaster.

    If you want to build you own controller for the heater core, use a Triac circuit. You won’t need a snubber on the Triac because you are not controlling a motor, or anything that will produce back EMF when the power drops.

  5. Jesus people, you all complain if it ISN’T a hack, now you’re complaining that it IS a hack… WTF?

    The guy did something. Give him some credit. And Kudos to hack a day for showing a real hack again, instead of just new development stuff.

  6. you are all so mad he did this (wrongly?) and posted it.
    your even more mad that he got it to work and you did not think of it.
    are you seriously expecting an appology from the guy?

    maybe it’s YOU who should be sorry for NOT donating
    the _”_REQUIRED_”_ proper equipment ?

    PS: a cracked tube does not always mean the vaccume has been let out/in.
    it means the contents of the tube are not correct for proper operation.
    often stress/heat/solder/jarring cracks appear that form SLOW LEAKS,
    tubes that normally do NOT have a glow between plate and emmitter will start to emit that (very dim) glow and consequently stop working to spec.
    IE your output transformer might start to saturate-with-DC/smoke/burn.

    you might need to kill heater and maintain B+ to actually SEE the glow as the filiment cools.
    PPS: killing heater-supply and maintaining B+ will often strip/damage the cathode/emitter and it is only reccomended on a bad tube or on a worn out spare. (resistor instead of transformer)
    PPPS: some tubes emit this glow during normal operation and it is bright enough to see with filament on.

  7. Alright everyone, lets sing it together (and be sure to use your best Barney Fife voice)…

    If it’s stupid and you know clap your hands (clap clap), and we’re all here to tell ya don’tcha know it (clap clap), if it’s stupid and you know it, yet the valve didn’t totally blow it, then it all worked out ok in the end (clap clap).

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