Photo from ?? Thanks, Mike Guerrucci. This is a simple device. That means it’s just a buzzer and a battery. And it has a super sensitive magnetic switch. This detector is always open until it is disturbed by a magnetic field. They call it a magnetometer. One way to make this is to use a
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From a reply on FB I built a speaker for a swimming pool. It was a large can of steel with an audio transformer mounted inside. The ‘I’ laminations were removed so the ‘E’ laminations could be very close to the end. I drove it with a 2N3055 on a heatsink. The secondary winding must
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A detector or discriminator in an electronic device might need to be adjusted to a very few points on a scale of a hundred or more points. A digital indicator typically indicates only a fraction of that, possibly 16 points. This is why the analog meter is still useful: it can indicate a small change
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Here is a handy (but limited) cross reference of various core materials from various manufacturers. The material type, such as 43 or 73, applies to types of cores other than toroids. The Fair-rite 2673002402 uses 73 material and makes a very good choice for a Joule Thief core. Another choice is the 2643002402, which uses
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When the winding gets tough, double up the number of toroid cores, I say. This JT uses toroid cores that are less than 1/4 inch (6.4mm) outside diameter. The wire has to be fine to get several inches wound on a core. So I wound one core with the wire, and then coupled it to
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This photo was posted to the files section of the Yahoo group lost_technology. I’m including it here so others don’t have to sign up or log on to see the photo. Since this was from a group for antique stuff, we will assume that this radio circuit is very old and uses Germanium transistors. The
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I bought a few bricks of 40 AAA cells at Fry’s, mainly because they were only $4.20 each, or about ten cents apiece – that’s cheap! But I really needed AAA cells because of all the Fenix LD01 and similar flashlights I now have. But I have so many AAA cells that I’ll never be
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