A Homemade Tube Amplifier Featuring Homemade Tubes

With the wealth of cheap and highly integrated audio amplifier modules on the market today, it takes a special dedication to roll your own from parts. Especially when those parts include vacuum tubes, and doubly so when you make the vacuum tubes from scratch too.

Now, we get it — some readers are going to find it hard to invest an hour in watching [jdflyback] make a pair of triodes to build his amplifier. But really, you’ve got to check this out. Making vacuum tubes with all the proper equipment — glassblower’s lathe, various kinds of oxy-fuel torches, all the right hand tools — is hard enough. But when your lathe is a cordless drill, and you’re using a spot welder that looks like it’s cobbled together from junk, your tube-making game gets a lot harder. Given all that, you’d expect the tubes to look a lot rougher than they are, but even with plain tungsten wire heaters and grids made from thick copper wire, they actually work pretty well. Sure, the heaters glow as bright as light bulbs, but that’s all part of the charm.

Speaking of charm, we just love the amp these tubes went into. Built in 1920s breadboard-style, the features some beautiful vintage mica capacitors and wirewound resistors, plus a variable resistor the likes of which we’ve never seen. The one nod to modernity is the clever use of doorbell transformers, one for a choke and one for the speaker transformer. They don’t sound great, but there’s no doubt they work.

We may have seen other homemade vacuum tubes before — we even recently featured a DIY X-ray tube — but there’s something about [jdflyback]’s tubes that really gets us going.

23 thoughts on “A Homemade Tube Amplifier Featuring Homemade Tubes

      1. Sorry if I came across as flippant here, I very much respect this work – I have an idle fascination with the idea of what could a timetraveler to 1890-1910 do from a technological point of view with the information in their head…

        I have a copy of Instruments of Amplification : Fun with Homemade Tubes, Transistors, and More https://amzn.eu/d/7X1mFSx and found it a very interesting read, and quite possibly the sort of thing the project creator would have used for reference, as it is very practical/hands on hackery, alas such skills are outside of my scope – but it is always interesting to see what enthusiasts can do with basic tools.

  1. Always wondered:
    What if the transfer function of Lee deForest’s homemade tube was non linear or less stable. Would we have electronics today? In reality this *is* the deForest triode. It’s amazing how well it works.
    If you built a tube in outer space, would you need anything other than a heated cathode, a grid and anode and not really need a vacuum vessel? Could you build a travelling wave tube on the moon out of just (well designed) chunks of metal with a heater?
    Interesting project.
    I love primitives. It would be cool if he would wind his own capacitors from foil, paper and wax, make resistors from carbon rods and wind his own transformer. Run it all from batteries, etc. Nice project!

    1. In Rocketship Galileo by Robert Heinlein, one character does imagine how easy it woukd be to build tubes on the moon.

      But what about dust? Glass keeps the vaccuum in, but any outside objects out.

    2. Before he became a publisher, Hugo Gernsback sold “wireless kits”.
      For resistors, he used graphite from a pencil manufacturer. But he was having trouble getting uniformity in resistance. So, he visited the pencil manufacturer (IIRC they were both located in NYC). There he found out the graphite was mixed with varying amounts of clay before being fired in the kiln. He was able to get uniform batches of the graphite from the manufacturer after that.

  2. Actually a vacuum isnt required, lack of readily oxidizing atmosphere is. There were mercury vapor and neon filled tubes for power circuits back in the day. A bit of magnesium hooked across the heater circuit and your volitiles become lessened.

  3. I suggest the maker may want to turn down the filament voltage a little, to an orange glow; at the intensity shown, I don’t think the filaments will last very long. It would be a shane to have early failure, as it had to have been a lot of work to make those tubes. At the proper voltage, the maker should never gave to replace them. But, all in all, a great project! Kudos.

    1. She’s using a bare tungsten wire for a heater and as she demonstrated with her tube tester the tube won’t conduct unless the filament is glowing that brightly (around 2200 °C.) She would have to use a coated heater in order to get the tube to work with just an orange glow.

  4. Once had that discussion with an electrical engineer about that. In a vacuum of space no glass envelopes needed. Then replace the heater with a radioactive electron source. You might be able to miniaturize tubes quite well. His comment? Might just work for low power applications.

  5. about vaccuum tubes not needing an envolope in space thing…
    space is less “empty” then you think…

    you get charged particles from the sun
    you get corrosive gases
    you got dust, lots of dust, some of it also corrosive andor radio-active
    and this all blows in the wind

    this is all not counting that fact that (i believe) space-wind is incredibly fast…
    theres just not enough atoms in the wind for us to notice it,
    until a small chunk comes flying at us at enough speed to slice through solar-panels,
    THEN we notice… one watt-at-a-time

    sand-blasting, acid-baths, and free-protons (hydrogen with no electron)

    so yeh, it’d work… at DC, for a little while…
    might make a good detector for alpha-radiation tho.

    PS: two tubes near eachother might swap electrons and intefer with each-other.

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