Dr Bruce Griffiths wrote: > 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 >>> time-nuts@febo.com >>> 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 >> time-nuts@febo.com >> 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 > time-nuts@febo.com > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > > Jason
Table 8-4 p61 in the service manual is probably a more accurate guide to the AC and dc voltages expected at the emitter base and collector of various transistors in the oscillator circuit. Bruce _______________________________________________ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
