This ham radio is unsafe at any frequencyWhen we were kids we rode bicycles without pads and helmets. We drank sugary drinks. We played with chemistry sets and power tools. We also built things that directly used AC line current. [Mike] remembers and built one, presumably more to discuss the safety precautions around things that can shock you and not entice you to duplicate it. He calls it The Retro QRP Widowmaker, if that’s any kind of a hint. (Video of this unsafe transmitter also embedded below.) The design showed up from time to time in old electronic magazines. Built on an open board and with no ground wire, the radio didn’t need a complex power supply. This wasn’t limited to transmitters, either. Some TVs and radios had a “hot chassis.” That’s why we were taught to touch an unknown chassis with the back of your hand first. A shock will contract your muscles and that will pull your arm away instead of making you grab the electrically active part. For safety’s sake, [Mike] used an isolation transformer to keep from having a disaster. A big resistor drops a lot of voltage to supply the tube in the circuit. There was a neon bulb to indicate if you have your plugs the wrong way around making things dangerous. We enjoyed [Mike’s] excellent code using an old J-38 style key. Not everyone uses a paddle or a keyboard. Nowadays, you don’t need high voltages for little transmitters. Also, $50 today is probably worth less than $10 was back then. If you have a hankering for vintage gear, try old transistors, instead. Source: • Our thanks to |
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