Heathkit Bites the Dust
Filed by
Jon Titus
on
05/11/2012
Under
Electronics
General
As a high student and electronics enthusiast I relished the arrival of each new Heathkit catalog that let me dream about all the equipment--from power supplies to amateur-radio transmitters and receivers--I might one day build. I can't remember the first Heathkit I built in the 1960's, but bet it was either a vacuum-tube voltmeter (VTVM) or a "Q multiplier" for my Hallicrafters short-wave receiver. While in college and grad school I built power supplies, an oscilloscope, signal generator, counter/timer, and a computer. Instead of studying for a quantum-mechanics final exam I built a Heathkit HiFi receiver/amplifier. (I passed the exam.) I liked to build the kits and learn about electronics from the circuit descriptions and schematics included in the kit manuals. Several people I knew had built color TVs from Heathkits. At the time, that was quite an accomplishment because the kit required numerous tests and circuit adjustments. See More ...
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Electronics Books and Kits for Summer Vacation
Filed by
Jon Titus
on
05/07/2012
Under
Electronics
Jon Titus
General
Keep Your Eyes on Iris-Identification Security Tests
Filed by
Jon Titus
on
04/25/2012
Under
Electronics
Jon Titus
General
Can You See a Future for Video Glasses?
Filed by
Jon Titus
on
04/16/2012
Under
Electronics
Jon Titus
General
Watch Those Relay-Coil Specs
Filed by
Jon Titus
on
04/10/2012
Under
Electronics
Jon Titus
General
When you need an electromechanical relay, remember to look at the specifications for coil voltage and current. You don't want to end up trying to control a relay coil that needs 25 mA with only a 5-mA current. And keep in mind that AC and DC coils have different construction and characteristics. In a DC coil, the wire’s resistance limits current, but in an AC coil, impedance at 60 or 50 Hz plus the coil’s DC resistance limit current. A DC coil has a problem with AC current because that current drops to zero twice during each cycle. Thus relays can produce a characteristics hum or buzz. To overcome this problem, manufacturers include a copper “shader ring” at the end of the coil closest to the ferromagnetic armature. The shader ring forms a shorted secondary coil that passes through the center of the coil as shown in my nearby photo and indicated by the red arrow. See More ...
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