>> The only thing I could provok, was that almost all capacitors I >> tried were sensitive to touch.
Most ceramic caps are sensitive to "micro phonics" via the piezoelectric effect, which can translate mechanical stress into electrical noise. https://e2e.ti.com/blogs_/archives/b/precisionhub/archive/2014/12/19/stress-induced-outbursts-microphonics-in-ceramic-capacitors-part-1 Wayne On Mon, Feb 26, 2018 at 2:05 PM, Poul-Henning Kamp <[email protected]> wrote: > -------- > In message <CAD2JfAjxVwO3coVTivD-Yp=XZqd78WKBDwKD0KA9fc8dq6GeOQ@mail. > gmail.com>, paul swed writes: > > >I reverse engineered the system and guess what cap was bad? The > integrator. > >So not being all that smart, I hooked 2 X 10 UF caps in series. Been > >working like a champ for 18 years. > > That capacitor isn't nearly as important as people think. > > The input signal to the integrator is continuous and jump-free and > the relevant timeconstant is sub-second. Dielectric absorption > doesn't matter when there are no voltage jumps. > > We all tune the EFC of the Xtal to set the meter to zero CONTROL > voltage, which means there is no voltage for the capacitor to leak, > so that doesn't matter either, > > If you pick a capacitor with a couple of hundred volts rating, its > leakage current will be less than the air and the PCB near it anyway. > > When I experimented, I could hardly find *any* property that mattered > for that capacitor, not even the exact capacitance, because the > adjustment procedue handles that. > > The only thing I could provok, was that almost all capacitors I > tried were sensitive to touch. > > I didn't establish if this was mechanical (and if so if it was the > capacitor or something else on the board) or if it was thermal > (capacitors have astounding tempcos). > > HP tied two O-rings around the capacitor they choose, I pressume > that is a clue that they found something similar. > > The biggest issue is probably that most of the relevant capacitors > are square blocks, like for instance TDK/KEMET B32774D8505K. > > TDK/KEMET C4GAJUD4500AA3J could be an option, but I suspect it > is too big to fit in the existing PCB. > > Either way, cheap and plenty available. > > -- > Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 > [email protected] | TCP/IP since RFC 956 > FreeBSD committer | BSD since 4.3-tahoe > Never attribute to malice what can adequately be explained by incompetence. > _______________________________________________ > 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.
