4 Tube Superhet

Posted on Feb 4, 2014

The theory of operation has already been covered either in the Simple Superhet or the All American Five. Building this radio is really not hard especially if you have been working along through the circuits in the order I have presented them. The variable capacitor is one I happened to have on hand but there is one like it listed in the Antique El

4 Tube Superhet
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ectronics Supply catalog and on their web site. It is a 3 section 30 to 470 picofarad per section. This is not the best for the AM band but it`s all I have. The ideal capacitor would have one section smaller than the other two. If you have or can get one by all means get it and use it. Some variable capacitors have what look like screws on the side; one for each section. People who are not knowledgeable about electronics will sometimes tighten up these screws because they in fact are loose. These screws are small adjustable capacitors. As the screws are tightened the metal plates, which are separated by the insulating mica, are pressed closer together thus increasing the capacitance. These are shown in the schematic diagram as variable capacitors in parallel with the sections of the main tuning capacitor. If you have one of those tuning capacitors with one small section and it has three trimmer capacitors on it you can skip the rest of this section and the entire section on the padder capacitor. If you are still reading you have a tuning capacitor like the one I have. Mine has only one trimmer built in and it is on the center section. If yours has three trimmers you will need one less external trimmer than I did. Use the front section (closest to where the shaft comes out) as the oscillator tuner. Loosen this screw until the trimmer has expanded as much as it will. If you need to add one or two trimmers use 7 to 45 or 10 to...

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