A Dozen Tubes Make An Educational Amplifier

If you asked [Hans_Daniel] what he learned by building a tube audio amplifier with a dozen tubes that he found, the answer might just be, “don’t wind your own transformers.” We were impressed, though, that he went from not knowing much about tubes to a good looking amplifier build. We also like the name — NASS II-12 which apparently stands for “not a single semiconductor.”

Even the chassis looked really good. We didn’t know textolite was still a thing, but apparently, the retro laminate is still around somewhere. It looks like a high-end audio component and with the tubes proudly on display on the top, it should be a lot of fun to use.

Of course, there were issues to work out. You can read his story about his transformer problems and there is a ground problem generating some noise. The amp can deliver 15 watts without noticeable distortion, according to [Hans]. We were a little sad though that there wasn’t an audio clip or a YouTube video so we could hear for ourselves.

We’ve certainly seen quite a few tube amps over the years. If you want a 1963-vintage education on how they work, you only have to watch the Army video below that we covered some time back.

16 thoughts on “A Dozen Tubes Make An Educational Amplifier

          1. You start with an empty elevator or bus, and you add one person to it.
            Then you add another
            and another
            and so on.

            Clearly you can just keep cramming one more person into an elevator or a bus. So there could be an infinite amount of people in one.

    1. i was thinking that too, I’d like to see his schematic. The “typical” amp uses 5 tubes, and back in the day companies that were bragging about more tubes in their amps were basically including hot spares and things like that. I can’t imagine what he’d do with so many tubes, but I’d love to see it.

      1. The schematic is there although a little hard to read. There are two channels and he mentions many of the tubes are dual triodes. So I would think 2×2 push pull outputs = 4. The driver looks like a dual triode so that 2 (accounting for both channels) so we are up to 6. The phono preamp uses a dual, so that 2 (one for each channel; 8 total). Then another dual for the tone control/preamp x 2 give you 10.

        The only way I can get to 12 is if he has two separate rectifiers, which he might. The schematic clearly says “only one channel shown” and there’s no note that the rectifier is a 1 off.

        1. The 12th tube is probably the one front and center in the photo of the finished amplifier. I’m guessing that it’s in the center-left portion of the schematic and is acting as a meter driver – the meter being the circle with an arrow through it.

    1. my thought exactly!
      When I read “he went from not knowing much about tubes to a good looking amplifier build”, I thought “ehh, yeah, sure… but how does it sound?”

      I can imagine that if he knew nothing about telescopes but yet he managed to build one and made it look good, yes, then I would have understood. But now I’m confused.

    2. In the good old times, the tubes were well hidden behind wood and metal. Simply because people did not like being zapped by non-isolated anode voltages of 300 to 700 V, or burn their fingers on hot glass. Radios and amplifiers looked like furniture, and rooms were illuminated by lamps, not by entertainment systems featuring cheep low-power tubes.

  1. “We were a little sad though that there wasn’t an audio clip or a YouTube video so we could hear for ourselves”

    Right. Cos nothing can quite as accurately convey the fidelity of an acoustic event like compressed digital streamed at 128k and excreted through a laptop’s 1″ speakers, or some beige desktop wonders. ;-)

  2. Interesting that the carbon mic in the instructional video didn’t have a DC applied to it. the narrator explicitly said carbon microphone.. Without DC the changing resistance has nothing to modulate

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