Hi, Garey, et.al.: Your explanation of the various crystals for the 4-line made me grab my Drake 4-line manuals and look through them. The circuits for all of the crystal oscillators in the receivers, except the R-4, and the transmitters are virtually, if not, identical. Those would use the series resonant crystals.
The R-4 manual states "Only parallel resonant third overtone crystals designed for a Miller oscillator should be used." From the circuit it is fairly obvious that parallel resonance is required. I have used parallel resonant crystals in some of the 4-line radios and, yes, the dial and/or skirt has to be repositioned if those crystals are active if calibration is desired (handy if you are at a band edge). The T-4X manual cautions, "When ordering, be sure to specify whether the crystal you are ordering is for a T-4X or R-4. They are not the same!" (the exclamation point is Drake's). Curiously, Drake has in the T-4XB manual (page 25) this statement: "R-4, R-4A, R-4B and T-4X, T-4XB crystals operate in the series mode and are interchangeable." Note that the R-4 is included in the list. I wonder if Drake decided after the R-4/T-4X that carrying two crystals for the same band but different resonances didn't make a lot of economic sense. In any case, as Garey implies, each crystal has two resonances and the circuit defines in which mode it will operate. 73, Bob K9JU
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