Interesting.  I'm inclined to say I stand corrected, BUT:  (i) as Mark
noted, the datasheet link points to the datasheet for Vishay FC Series
HF thin-film resistors [which are really excellent low-reactance T/F
resistors, if you need any]; (ii) I cannot find any reference to PC caps
on the Vishay/BC web site; and (iii) other distributors do not list this
cap (or any Vishay/BC PC caps, for that matter).

I did discover Electronic Concepts (ECI) (https://www.ecicaps.com/), who
claim to make their own PC film and do seem to supply three series of PC
caps.  They seem mainly to make them to order, but they have small
quantities of some parts in stock.  Prices are by quotation, so I don't
know what they charge.  I assume they are pretty pricey, and if they run
out of an in-stock cap there may be a minimum order to get more.

So, I do stand corrected.

All that said, PP and PPS are the best choices for the A9 integrator
project.

Best regards,

Charles

On 2/24/2018 9:35 PM, Mark Sims wrote:

The part number BFC234421475, on http://www.wima.com.ua/BFC234421475
seems to be a Philips product, 2500 available, for 49.28 UAH
(Ukrainian Hryvnia, that is 1.77 USD). A mysterious capacitor...

On Sun, Feb 25, 2018 at 12:35 PM, Charles Steinmetz
csteinmetz@yandex.com wrote:

Am 25.02.2018 um 13:46 schrieb Azelio Boriani:

Why not go to Mouser or DK, as usual?

Or to the source itself:
<  https://www.wima.de/en/  >

(Abt. an hour of driving from where I'm now).

BTW last time I bought some at DK/Mouser, there was
a pricing artefact, in that 5% was cheaper than 10%

:-)  Gerhard

Well all this capacitor talk has me actually looking for the 5 uf cap.
When I picked up the 5065a it didn't work. This was in the late 90s and no
manual was available at that time.
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.
Not obvious of what the downside of this approach was at all.
But I went out to mouser and have to say the selection of large capacitors
really is thin for PPS and PS. I did see the one picture of a yellow cap I
think from Germany.
The question really is what is the source and part number for a good cap.
does appear that the wima caps are carried by Mouser but may have long lead
times.
Regards
Paul
WB8TSL

On Sun, Feb 25, 2018 at 2:50 PM, Gerhard Hoffmann dk4xp@arcor.de wrote:

In message CAD2JfAjxVwO3coVTivD-Yp=XZqd78WKBDwKD0KA9fc8dq6GeOQ@mail.gmail.com, paul swed writes:

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@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.

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@phk.freebsd.dk
wrote:

In message CAB+jonC9HVv9826ocWmTdTEC-mr8JJ+G-Vw_teSO4BnMO0B-dg@mail.gmail.com, Wayne Holder writes:

Yes, and unlike plastics, their mechanical resonance is sharp and
at frequencies where microphonics matter a lot.

Even then, a 4.7uF SMD multilayer ceramic mounted with two "looped"
wires for stress-relief worked just fine.

--
Poul-Henning Kamp      | UNIX since Zilog Zeus 3.20
phk@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.

Poul-Henning wrote:

That is a very common misconception, probably fostered by the usual test
methodology for DA.  But it is not correct.

DA is a charge-migration phenomenon, so it occurs whenever the charge
on a capacitor changes.  A step function in the charge very obviously
represents such a change (and for this reason is used for testing the
parameter in most circumstances), but so do gradual changes in the
driving charge.  These can be less obvious (than step changes),
depending on the time scale of the change relative to the time scale of
the DA process in the particular capacitor.

There are several dimensions to DA -- not just how much charge isn't
returned immediately, but what the "tail" looks like (i.e., the time
profile of charge return, generally measured as current vs. time).
Different dielectrics (and, to a certain extent, different construction
techniques) exhibit different charge-return profiles.

Long-TC integrators do tend to mask the effects of DA, because the time
scale of changes in the driving charge is closer to the time scale of
the delayed charge return caused by DA.  But that does not mean that DA
isn't important, because slow integrators are frequently used where
extremely high precision is required (such as integrators for
high-resolution DACs and EFC servos for precision oscillators), so the
tolerable amount of delayed charge return is extremely low.

As with any circuit, the A9 integrator is "good enough" when the errors
it causes are swamped by other accumulated errors.  But I'm no fan of
"just good enough" design, particularly in a case like the 6065A where
time nuts are diligently working to improve the performance of the
instrument.  Some times, "just because it's better" is a sufficient
reason to overdesign, particularly where the incremental cost is low and
especially where the projected number of units is low, both of which are
true WRT the improved A9 board.

Best regards,

Charles