[time-nuts] Replacement A9 boards for the HP 5065A

[Wayne Holder]

>> 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 <phk at phk.freebsd.dk>
wrote:

> --------
> In message <CAD2JfAjxVwO3coVTivD-Yp=XZqd78WKBDwKD0KA9fc8dq6GeOQ at 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
> phk at FreeBSD.ORG         | TCP/IP since RFC 956
> FreeBSD committer       | BSD since 4.3-tahoe
> Never attribute to malice what can adequately be explained by incompetence.
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