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| As a collector and enthusiast of antique tube radio, i have looked with great interest at your schematics. In a simple observation I am curious as to the possible use of tubes for a stage or two where applicable. In the early days, when only basic triodes were used like the infamous 01a tube AM radio would consist of several tuned RF amp stages with a final tube amp like the 112A tube. These fed a speaker of high impedance instead of the modern 8 ohm type speakers. Inrealization that these designs were the 'norm" during Edisons time I am curious where such design might be of a particular advantage from such "forgotton technology". In the case of modern superheterodyne radios a local oscillator is employed which inherently presents a frequency by itself that could possibly interfere with an items function. I believe all of the AM Ics that you will remove from car audio will be of a superhet on a chip. Perhaps these items themselves could be improved by the elimination of the superhet oscillator.In the "echo box' it would be interesting to see if an old high impedence speaker would perform any better although it would of course have limited frequency response. Limited frequency response could possibly be a plus considering how little of the audio spectrum is required for understandable human speech.Have you measured if possible the maximum audio frequency deviation of the voices? An audio frequency spectrum analyzer might help to analyze what spectrum is used , and what could be disposed i.e filtered out.This is just a few thoughts by an observer.Best regards, Phil |
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on Jan. 15 2008 |
