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History of the company that invented and patented the overtone crystal, etch-to-frequency and variable crystals. Source for ads, engineering bulletins, patents and manuals.
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FT243 information compiled by Paul Carreiro, N6EV.
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A handy historical chart of old crystal holders with dimensions, and suppliers.
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From N6EV. Tube oscillator schematics, and discussion.
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WB6SZS, Eugene Rippen's chart for crystal use on the HF, VHF and UHF bands.
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A useful technical reference page for Crystals.
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