Hi Simple approach is to assume that you have a crystal resistance in the range of 100K ohms. If you guess to high, the oscillator will just work to well :)
Multiple JFETS in cascade for the higher frequency stuff should work. For anything below 20 KHz, an op-amp is likely your best bet. A spectrum analyzer with a tracking generator will give you some idea of their impedance and *if* they still have any activity at all. Bob > On Jun 4, 2016, at 4:46 AM, Mike Cook <[email protected]> wrote: > > Hi, > > I have a number of crystals either in glass, bakelite, ceramic or metal > housings that I would like to get resonating . They are of three basic types. > Square, or rectangular flat > Round flat > Bar square section > Sizes range from 2-10cm or more in the longest face. > > Some have frequency markings. ranging from IKHz 5MHz. > Others have none. > Some are of Military origin, probably radios and as they have markings I can > probably find a schematic from the radios to see how to proceed. There may > be dedicated testers still around. I am not so interested in this bunch at > the moment. > Others have no known origin so I have no idea what oscillator circuits were > used with them. > In terms of vintage, I would guess pre 1940 to late 50s > > I have built a little Pierce circuit an tried a few. Some of the later 1-5MHz > crystals will oscillate but there are a lot of parasitic signals as well as > the supposed fundamental. I cannot make any of the low frequency / big > crystals to react. > > So my question: > If you had a crystal with unknown frequency and drive requirements that you > wanted to investigate. How would you go about it? > > If I can get them going I will share the Adevs. I don’t have a spectrum > analyser so I can’t do phase noise. > > Regards > > "The power of accurate observation is commonly called cynicism by those who > have not got it. » > George Bernard Shaw > > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
