Filter Choke Analyzer

Posted on Feb 4, 2014

The familiar transistor power supply has one big mother of a filter capacitor on the rectifier output followed by an electronic regulator which regulates out all voltage variations including ripple. In vacuum tube days only the very tip top of the line test equipment (Hewlett Packard, Tektronics, General Radio, etc) used electronic regulators. So it was necessary to

Filter Choke Analyzer
Click here to download the full size of the above Circuit.

find a way to filter out most of the ripple using passive components (not tubes). In many devices such as low cost radios and phonographs the designers managed to use resistor-capacitor RC filters but if the current drawn by the circuit was large and the application demanding, such as a Hi-fi power amplifier, the power supply needed an inductor-capacitor (LC) filter. An inductor needs to have many turns of wire wound on an iron core. The wire must be heavy enough to have a low enough resistance so it can conduct the direct current without dissipating an excessive, usually five watts or less, amount of power. The core had to have enough iron in it so as not to saturate at the maximum specified current. Filter chokes are getting hard to find they mostly are seen at electronic flea markets (hamfests) and from dealers on the net who specialize in antique electronic parts. If you`re a retread like me you may have some stored in your basement or garage. It is very likely these old chokes whether in your garage or from a flea market won`t be marked with specifications. Don`t despair. Ve have vays of finding out zese sings. It`s not enough to just measure the inductance of a choke. You need to know how it behaves when carrying a mixture of AC and DC. The simplified circuit is shown here. The transformer isolates the test circuit from the line and provides some step down. The secondary delivers very little Alternating Current but...

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