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On Sep 7, 2:43�pm, Michael Black wrote:
Nobody has ground their crystals from scratch since about the 1930's, if even then. �I've been licensed since 1972 and in all the time since then I've never seen anything about it, not in magazines and books going back to the late 1940's and not in more recent material. There were articles in QST in the 1920s about cutting and grinding your own crystals from the raw quartz, making holders, etc. A lot of work and specialized equipment. The market was such that the specialists quickly took over in the early 1930s. After WW2 the enormous amount of surplus dominated the amateur market for decades. Many of the "new" FT-243 crystals we bought were actually surplus holders with new crystal inside. �I do recall the 1964 article in QST about a buy in SOuth America who made his own tubes. There's a guy in France doing it today. Has a movie on his website. But again, lots of work and specialized equipment. Go back far enough, and hams just needed crystals within the band. They had relatively little need for exact frequencies. Well, yes and no. Some xtal frequencies were more prized than others, because the harmonics fell in higher bands. I suspect even if the Handbook did give such details at one time, little bits may be lost since when something is current, "everyone knows" things that may not be obvious to someone who comes later. That's true of many things. Reading older radio books and magazines can require knowledge of a lot of the jargon and methods of the day. Now, they need them on exact frequencies, and they want them in nice small packages, none of those FT-243 ones that were held together with pressure. The big difference is plated electrodes vs. pressure electrodes. FT-243s are capable of quite good accuracy; .005% was common, which works out to 200 Hz at 4 MHz. Pre-WW2 xtals were big and rugged, but used a lot of quartz. Radio- grade natural quartz came almost exclusively from Brazil, and the difficulty of supply caused US xtal makers to develop xtal designs that used less quartz. The FT-243 was ultra-miniature in its time! 73 de Jim, N2EY |
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