Spy Transceiver Makes Two Tubes Do The Work Of Five

Here at Hackaday, we love following along with projects as they progress. That’s especially true when a project makes a considerable leap in terms of functionality from one version to another, or when the original design gets more elegant. And when you get both improved function and decreased complexity at the same time? That’s the good stuff.

Take the recent improvements to a vacuum tube “spy radio” as an example. Previously, [Helge (LA6NCA)] built both a two-tube transmitter and a three-tube receiver, either of which would fit in the palm of your hand. A little higher math seems to indicate that combining these two circuits into a transceiver would require five tubes, but that’s not how hams like [Helge] roll. His 80-m CW-only transceiver design uses only two tubes and a lot of tricks, which we admit we’re still wrapping our heads around. On the receive side, one tube serves as a mixer/oscillator, combining the received signal with a slightly offset crystal-controlled signal to provide the needed beat frequency. The second tube serves as the amplifier, both for the RF signal when transmitting, and for audio when receiving.

The really clever part of this build is that [Helge] somehow stuffed four separate relays into the tiny Altoids tin chassis. Three of them are used to switch between receive and transmit, while the fourth is set up as a simple electromagnetic buzzer. This provides the sidetone needed to effectively transmit Morse code, and is about the simplest way we’ve ever seen to address that need. Also impressive is how [Helge] went from a relatively expansive breadboard prototype to a much more compact final design, and how the solder was barely cooled before he managed to make a contact over 200 km. The video below has all the details.

Thanks to [Stephen Walters] for the tip.

26 thoughts on “Spy Transceiver Makes Two Tubes Do The Work Of Five

  1. That is an awesome design and construction Helge. To squeeze that sort of functionality into a little metal Altoids box is amazing. I am not into valve radios at all I just usd to pull them apart as a child. They still hold a magical fascination for me though.

  2. A very nice and compact design. Looking at the circuit, it makes sense to me but I would have a hard time fitting it into the little tin. Great job :-) de WA4JAT

  3. This article is a perfect example of a pet peeve of mine. I know you want me to go watch the video which I probably won’t, but couldn’t you at least include a couple of photos of the interesting parts… in this instance the breadboard and the inside of the final version?

    1. Not sure why you feel the need to disrespect other peoples transceiver designs. Their requirements are their choice.

      It’s funny though, when I searched for the article you mentioned I noticed that back in 2014 you were doing the same thing to designs related to the one you referenced.

      There is no one transceiver design with a single set of requirements.

      Maybe you should recognize people have different interests than your own, which largely seems to be disrespecting other peoples work.


      1. I mean. Ham radio in general is mostly useless if we’re being honest with ourselves here. You can send a text from the loop with a cellphone to the other side of the world. And I’m an unapologetic ham. If people paid us to do stuff it’s a job. If you pay to do it I call that a hobby.

        1. Believe it or not, a few hams/swls still do have ideals. They see more in ham radio than an utility for communication. It’s a way of life to them, rather. They participate it because they are curious and want to evolve. It’s not just a sport, either. Some of them avoid contests like the pest. They rather listen, be it ham bands or something else. We may call them a silent majority, maybe. Not sure. Not all like adore shortwave, either. Some are into EME, VLF or satellites. Or radio links (microwaves), optical links (laser).. There’s a lot more than shortwave and 2m/70cm repeaters. Also, some are hams but don’t do radio stuff so often. Rather, they focus on electronics or other technical fields. Many computer pioneers of the 70s/80s were hams, too. They just didn’t brag about it all the time. That doesn’t mean they weren’t silently proud to be hams, though. Being a ham helped them getting in touch with other similar minded people of other scientific fields which were hams, as well. Being a radio amateur is more than having a license. It’s about having an open mind and a love for both technology and social interaction with people. Without the social component, ham radio is incomplete, just half of itself. The original “ham spirit” code of honour by Paul M. Segal (W9EEA) describes it rather well. Vy73

          1. I didn’t make my point very well. I’m saying hobbies don’t have to be amazingly useful or bleeding edge tech or whatever. They can be, but “for the love of the game” is good enough and doesn’t need to be justified. Just like all hobbies. I love radio for all the reasons you mentioned.

        2. “Ham radio in general is mostly useless” — Ham radio is going to be extremely NOT useless when a solar storm knocks out cell service for an extended time.

      2. Here’s my rose-coloured version of the story..: The transistor is a actually a step backwards.
        In the early days, there was the crystal detector, a solid-state/semiconductor device, which our glass diodes originate from. Then the valve was invented a while later, based on an ingenious idea of utilizing the thermionic effect. It was a device that didn’t exist as such in nature, a device born out of human’s creativity. Then the transistor occured, sadly, and things went back to grandfather’s old diode/semiconductor technology. Seeing its shortcomings and comparing it to the transistor, the field-effect transistor was born. A humble effort to catch up with the awesome tube technology. It was designed to imitate the behavior of the tube, but was very fragile and limited in its maximum frequency. Then, as a last effort, the tube makers created the Nuvistor, a pinnacle of both human’s mind and craftsmanship. It was low-power, small, well built, robust against big/strong signals, with a very low noise floor, low self-noise and a high frequency range. Unfortunately, the industry moved away from it because it lustered for higher profits the transistor was promising. Then tube development was halted, but it took nearly 20 years up until the transistor technology outperformed this “dead” technology. And they lived happily ever after..

        Epilog: Meanwhile, USSR being wiser than the US, had kept using miniature tube technology in its tanks and jets, which was immune against EMPs and thunderstorms. Fin. :)

        1. Inre: Your final sentence.
          I’m glad you put a smiley at the end of it, because it had nothing to do with more wisdom. Hollow state devices are not “immune” to EMP, but less susceptible. And being a central controlled “Union”, changes were hampered by the bureaucracy.

  4. I avoid Michael Black the “totally missing the point award”. Helge certainly knew he could do this solid-state, using tubes was a challenge and an aesthetic choice.
    I award Craig runner-up status. If you are an unapologetic ham then why bring up cellphones and criticize someone for doing something very ham-like?

    1. You clearly can’t read. Craig was responding with sarcasm to Black’s stupid comment about transistors. Black was talking about not using tubes because transistors has been invented. Craig is just throwing some gas on fire that you might as well go with cellphones with that logic.

  5. As a ham I think projects like this are fun, and doing it with tubes is a nice challenge. But from a distance we should admit that miniaturization that ignores the power supply skews the concept more than a little bit … and generally speaking, power supplies for tube gear are pretty large and rarely portable (as might be the reason for the miniaturization). Transistorized projects can at least claim to run off high capacity batteries.

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