[time-nuts] 10811 Repair (was warmup / bad batch)

Dr Bruce Griffiths bruce.griffiths at xtra.co.nz
Mon Jan 22 21:11:02 EST 2007


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
>
>
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>
>   
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



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