Dr Bruce Griffiths wrote: > Jason Rabel wrote: > >> What voltage goes to the crystal? I may have had my scope scale too high and >> just didn't notice, but at first glance I don't think it was getting power. >> >> Jason >> >> >> -----Original Message----- >> >> Yes, the black wires are the thermistor. >> >> The crystal has three wires. Two are actually connected >> to the crystal electrodes. The third is the case. The >> case is fastened to the casting with a screw. The only >> way the casting gets an electrical ground is by way of the >> crystal ground screw and ground wire to the board. >> The wires are welded to the crystal, so if you want to >> disconnect one of them, you have to unsolder it from the >> PC board. >> >> Rick Karlquist N6RK >> >> >> _______________________________________________ >> time-nuts mailing list >> [email protected] >> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >> >> >> > Jason > > There should be no dc (with respect to ground) on any of the crystal leads. > The ac voltage developed across the crystal is determined by the > parallel combination of the effective crystal inductance at the > operating frequency and the crystal ESR plus the impedance of the > trimmer network. Since the crystal current is 1mA rms (see HP journal > March 1981 p24) and the crystal ESR is around 50 ohms the AC voltage > across R4 in the schematic will only be about 50 mv rms. > > Bruce > > _______________________________________________ > time-nuts mailing list > [email protected] > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > > Jason
Since the oscillator circuit is checked by substituting a 10uH inductor for the crystal then the crystal impedance must be around 50 + j628 ohms at the circuit resonance. The trimmer network has an impedance of -j568 ohms and the common base transistor has an input impedance of about 8 ohms plus an inductance of a few nanohenries. with a 1mA crystal current the voltage across R4 is consequently about 80mV rms. Bruce _______________________________________________ time-nuts mailing list [email protected] https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
