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Makezine_COTM_Capacitor-BadgeInstructables user Jezan made an air variable capacitor:

I was building a crystal set for my son, but it came to a halt. When i found out that i have no variable capacitor in my pile of junk.
Scavenging one from an old radio was not an option. Since most of new radios uses analog tuning. And the ones with air variable capacitors are very rare, and are collectors item.

I have read an article once about building an air variable capacitor. So i decided to build my own from scraps of aluminum sheets and from things that are easily found around the house.

I love how Jezan built the capacitor out of scrap aluminum, using only basic household tools like scissors and a rubber mallet, along with salvaged scrap metal. [originally posted by SMR in 2011]

John Baichtal

My interests include writing, electronics, RPGs, scifi, hackers & hackerspaces, 3D printing, building sets & toys. @johnbaichtal



  1. MikeW says:

    Beautiful work! When in high school I bought old radios, TVs & other items & fixed them. your

    The capacitors that were used for tuning in the old radios had rotor plates that weren’t round. They were constructed so that the change in capacitance was non-linear, making the tuning linear. Also, the outermost plate had slits cut in it, these narrow pieces of metal could be used to linearized the capacitor, they were bent in & out and twisted to make the tuned frequency match the display. If size was an issue mica sheets were inserted between the plates, though this was rare in consumer items — later they used plastic sheets for dialectic (e.g. in transistor radios).

    There were also “trimmer capacitors”. Sometimes similar in construction to what you made, with just a couple of small plates. Usually made on a rectangular ceramic base, A rectangle of metal was the bottom plate. The top plate was a springy metal rectangle, and there was a piece of mica between for dialectic.

  2. kongorilla says:

    Anyone who digs this should definitely buy a copy of “The Voice of the Crystal” by H. Peter Friedrichs, a very cool book about building radio receiver parts from scratch. Even makers who aren’t interested in building a crystal set will find it pretty darn fascinating and educational.

    You can buy a copy from the Xtal Set Society’s online bookstore, or Amazon I suppose, but the Xtal site is full interesting stuff and is worth supporting.

  3. Trav says:

    Huh, never knew they were so scarce. I probably have 4 or 5 of them laying around in junk drawers that I have inherited. I was just thinking about getting in there and throwing out some of the old parts I will never use. Maybe I’ll try to find a better home for them. I also have some adjustable wire-wrapped resistors. Kind of like potentiometers, but meant to be fine-tuned and left alone.

  4. Derek says:

    just this afternoon, I collected my scrap power supply wire, wound it on a cardboard tube, connected it to my breadboard w/ a scrap var. cap.,diode,and 47k resistor, connected my tv antenna, and ground, and heard my favorite AM station! not bad for harvested parts!

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