Hi That was one of the reasons I was a bit amazed high school students were doing it as a lab exercise. The presence of high voltage here and there is something that you simply would not see in a similar school today …
Bob > On Feb 13, 2017, at 11:19 PM, Alex Pummer <[email protected]> wrote: > > just be careful, because if you under-heat the cathode you could kill it > > 73 > > Alex > > > On 2/13/2017 7:11 PM, Bob Camp wrote: >> Hi >> >> >>> On Feb 13, 2017, at 8:15 PM, Scott Stobbe <[email protected]> wrote: >>> >>> On Mon, Feb 13, 2017 at 6:41 PM, Bob Camp <[email protected]> wrote: >>> >>>> >>>> I think what you would find is that it *is* a fairly normal AT cut and the >>>> data book >>>> that came with the instrument plotted out the data for the specific >>>> crystal in >>>> the device. The usable temperature range was fairly small, so the plot will >>>> be pretty linear. >>>> >>> Attached is a plot of crystal calibrators temperature stability. Span is >>> roughly 65 degC. >> Which eyeballs out to be pretty close to an AT. Without knowing the PPM >> scale there isn’t much way to be sure. >> >>> One of the other aspects I think is intriguing is the DC PSRR of a vacuum >>> tube crystal oscillator. In the case of a bjt based oscillator you have the >>> C-V relation for depletion capacitance and the base-emitter dynamic >>> capacitance as a function of collector current. I would suspect that for a >>> one active device oscillator, tube vs bjt, a tube crystal oscillator would >>> be less sensitive to small power supply variations (+- 10% ). >> Except you *do* have miller effect which pretty much messes things up >> for a triode. A pentode is a bit less sensitive, but you still have issues. >> >>> Which is a >>> convenient attribute for a poorly/unregulated battery supply in the vacuum >>> tube case. Unless filament current has an appreciable impact on frequency, >>> I wouldn't think so… >> Umm… errrr …. check it out :) >> Oddly enough, I remember a high school physics lab where they had us plot >> the effect of filament voltage on plate current and gain. Seemed like a weird >> thing to do to me at the time. Turns out the teacher grew up with microwave >> tubes >> that were tuned by varying the filament. Who knew ??? Pretty strange stuff >> if >> you ask me. >> >> The bigger issue is the tubes get hot. The heat varies with supply voltage. >> Temperature change is the result. That temperature change messes up >> oscillator stability. You pretty much have to wait for things to hit >> equilibrium >> before you do useful stuff ( = let it warm up for an hour or four). >> >> Bob >> >> >> >>> <Lampkin105_CrystalTempCo.png>_______________________________________________ >>> 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. >> >> >> ----- >> No virus found in this message. >> Checked by AVG - www.avg.com >> Version: 2016.0.7998 / Virus Database: 4756/13950 - Release Date: 02/13/17 > > _______________________________________________ > 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.
