Discussion:
Replacement A9 boards for the HP 5065A
(too old to reply)
c***@juno.com
2018-02-24 23:45:06 UTC
Permalink
Hi,

I'm working to make some replacement A9 boards for the HP 5065A to the
new style schematic.

Will share the Gerber file when done.

The integrator capacitor is a 1986 vintage TRW 5.0ufd 50V 10% .42"DX1.0"L
axial.

Of course it has an HP part number and no manufactures #.

Any guess as to what type it is?

Polycarbonate, polypropylene, ???????

Just wanting to find a good modern replacement for its use. (Integrator
with a 50ms time constant.)

Thanks,

Corby

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Poul-Henning Kamp
2018-02-24 23:51:57 UTC
Permalink
--------
Post by c***@juno.com
Any guess as to what type it is?
Polycarbonate, polypropylene, ???????
I think the manual says polypropylene in the parts list ?
Post by c***@juno.com
Just wanting to find a good modern replacement for its use. (Integrator
with a 50ms time constant.)
The audiohomeopathy crowd claims to have PTFE/Teflon capacitors available
in these kinds of sizes and I've been meaning to buy one just to see if
it truly is PTFE or not, but list-prizes has nothing to do with reality.
--
Poul-Henning Kamp | UNIX since Zilog Zeus 3.20
***@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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Bob kb8tq
2018-02-24 23:56:31 UTC
Permalink
Hi

Teflon is the traditional “best of the best” for integrator caps. Simply finding
any plastic cap (other than a motor start device) up around 5 uf is not that easy
these days. As mentioned by PHK, being sure it is what it’s supposed to be ….
good luck.

Bob
Post by c***@juno.com
Hi,
I'm working to make some replacement A9 boards for the HP 5065A to the
new style schematic.
Will share the Gerber file when done.
The integrator capacitor is a 1986 vintage TRW 5.0ufd 50V 10% .42"DX1.0"L
axial.
Of course it has an HP part number and no manufactures #.
Any guess as to what type it is?
Polycarbonate, polypropylene, ???????
Just wanting to find a good modern replacement for its use. (Integrator
with a 50ms time constant.)
Thanks,
Corby
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Robert LaJeunesse
2018-02-25 01:29:35 UTC
Permalink
Not too long ago I designed an integrator for a piezoelectric force transducer. The customer wanted a rock-solid output after a step load on the transducer. The capacitor of choice was PPS, used in surface mount form and less than 0.5uF total capacitance. With a particular PCB material chosen for low moisture absorption the drift ended up being in the 200uV/minute range (4mV in 20 minutes!). The capacitor of choice was PPS, and Kemet uses that for its 4.7uF radial lead part number SMR15475J50B14L16.5CBULK. Not cheap, but it's what I'd look at first.

Bob L.
Sent: Saturday, February 24, 2018 at 6:45 PM
Subject: [time-nuts] Replacement A9 boards for the HP 5065A
... The integrator capacitor is a 1986 vintage TRW 5.0ufd 50V 10% .42"DX1.0"L
axial.
...Just wanting to find a good modern replacement for its use. (Integrator
with a 50ms time constant.)
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Gerhard Hoffmann
2018-02-25 01:34:36 UTC
Permalink
Post by c***@juno.com
Hi,
I'm working to make some replacement A9 boards for the HP 5065A to the
new style schematic.
Will share the Gerber file when done.
The integrator capacitor is a 1986 vintage TRW 5.0ufd 50V 10% .42"DX1.0"L
axial.
Of course it has an HP part number and no manufactures #.
Any guess as to what type it is?
Polycarbonate, polypropylene, ???????
Just wanting to find a good modern replacement for its use. (Integrator
with a 50ms time constant.)
50 ms integration time and 5uF+-20% does not sound like a
leakage current problem. Polypropylene seems good enough.
Teflon would be a joke. I might even go with WIMA MKS4
(Polyester) if I had them in the drawer. Dielectric absorption
is also not a problem at these impedance levels and time constants.

When I recapped the electrolytics in my 4274A RLC bridge, it was
hard to find capacitors that fit the board footprint of the old ones.
Usually I had to choose 2 or 3 times the voltage so that they would
fit the board.  But that is a luxury problem. :-)


<
https://www.digikey.de/products/de/capacitors/film-capacitors/62?k=&pkeyword=&FV=e340004%2Ce340007%2Ce340055%2C1f140000%2Cmu4.7%C2%B5F%7C2049%2Cmu5.1%C2%B5F%7C2049%2Cmu5%C2%B5F%7C2049%2Cffe0003e&quantity=0&ColumnSort=0&page=1&stock=1&pageSize=25
  >

Mouser.com  should have just as much.

regards, Gerhard


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c***@juno.com
2018-02-25 01:40:28 UTC
Permalink
Well I hunted up the change pages for the A9.

The cap is polycarbonate, the original A9 was polyester.

If I can't find the polycarbonate I'll look into the PPS.

Cheers,

Corby

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Charles Steinmetz
2018-02-25 03:45:45 UTC
Permalink
The key properties relevant to long-TC integrator capacitors are
insulation resistance (leakage) and dielectric absorption (DA). (One
response on this thread opined that DA is not important in this circuit,
but that is not correct. DA is most definitely a factor in long-TC
integrators, including this one.) If maintaining an absolute time
constant is important, then tempco enters the picture (but the absolute
time constant of the A9 integrator is not a critical parameter).

Consider polypropylene (PP) capacitors as the baseline for long-TC
integrator applications.

Polycarbonate (PC) capacitors are very scarce these days, because the
sole source of PC capacitor film discontinued it over 15 years ago.
Even if they were available, the advantages of PC over PP in this
application are small.

PPS has a lower tempco than PP, and may have lower leakage (depending on
construction and processing). They are generally not so easy to find,
particularly in larger values, but Robert already directed you to the
Kemet SMR series, which are available in suitable values and are
conveniently packaged.

Polystyrene (PS) is the best dielectric for long-TC integrators except
for Teflon (PTFE), but PS caps are extremely hard to find in large
values, are generally huge compared to PP and PPS, are easily damaged
during soldering, and are not conveniently packaged.

PTFE is the best dielectric for long-TC integrators, but PTFE caps are
expensive and huge, and they are unnecessary for this application.

Your best choices are PP and PPS. The DA of PP and PPS are similar. The
leakage depends as much on the construction and processing of particular
caps as on the bulk resistivities of PP and PPS, so look at the
datasheets carefully to see what is guaranteed by the manufacturers.

Best regards,

Charles
Post by c***@juno.com
Well I hunted up the change pages for the A9.
The cap is polycarbonate, the original A9 was polyester.
If I can't find the polycarbonate I'll look into the PPS.
Cheers,
Corby
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Charles Steinmetz
2018-02-25 04:44:16 UTC
Permalink
Returning to the topic of what op-amp to use:

Bert asked if the LT1793 is a good choice. I suggested the LT1012 as
superior in the specific parameters that will provide best performance
in the HP circuit
(https://www.febo.com/pipermail/time-nuts/2018-February/108964.html).
Attila suggested the LTC6240HV.

I continue to believe that the LT1012 is the best choice (or,
alternatively, the similar OP97 -- but the LT1012 would be my first choice).

As Attila noted, the 6240 is limited to +/- 5v supplies. I do not know
if the output voltage of the A9 ass'y needs to be able to swing beyond
+/- 5v, but I would not be inclined to change this without a lot of
careful thought (and adding another op-amp does not excite me). But
really, that is not necessary. Even if the 6240 could supply outputs up
to +/- 15v, the LT1012 would still be a better choice.

Given the relatively low resistances at the op-amp inputs (10k ohms),
the ultra-low input "bias" (leakage) current of the 6240 is simply
unnecessary. Any offset due to the input currents (within the general
range of any of these op-amps) is insignificant compared to the op-amp's
offset voltage. Thus, offset voltage, offset voltage tempco, and offset
voltage long-tem drift are the critical parameters (as Poul-Henning
pointed out). And here, the 1012 is clearly the best of the three. In
addition to having the lowest input offset spec, the 1012 has guaranteed
maximum specifications for these important parameters. The 6240 (for
good reason) is *not even rated* for long-term stability (drift).
(Long-term offset stability is a particular weakness of CMOS op-amps.)

Finally, as I noted before, the 1012 has an overcompensation pin that
may be useful to improve the damping and the wideband noise of the
integrator. (This would, of course, require a small amount of design
work to place overcompensation pole(s) and possibly zero(es) to best
advantage, but may provide significantly improved performance.)

Of all the op-amps I know and use, the LT1012 would be my first choice
for the A9 integrator board.

Attila also advocated using the "much cheaper and easier to solder TPS7A49
[and] TPS7A3001" voltage regulators, as opposed to the LT3042 and a
negative-regulator-to-be-named-later that I mentioned. I concur with
his suggestion.

Best regards,

Charles


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Attila Kinali
2018-02-26 14:53:21 UTC
Permalink
On Sat, 24 Feb 2018 23:44:16 -0500
Post by Charles Steinmetz
Given the relatively low resistances at the op-amp inputs (10k ohms),
the ultra-low input "bias" (leakage) current of the 6240 is simply
unnecessary. Any offset due to the input currents (within the general
range of any of these op-amps) is insignificant compared to the op-amp's
offset voltage. Thus, offset voltage, offset voltage tempco, and offset
voltage long-tem drift are the critical parameters (as Poul-Henning
pointed out). And here, the 1012 is clearly the best of the three. In
addition to having the lowest input offset spec, the 1012 has guaranteed
maximum specifications for these important parameters. The 6240 (for
good reason) is *not even rated* for long-term stability (drift).
(Long-term offset stability is a particular weakness of CMOS op-amps.)
Oh.. right, I didn't think about long term behaviour. Thanks for the correction!

BTW: How about using an LTC2057 then? Its input bias current and
GBW spec is similar to the LT1012, but its offset voltage and drift
are far superior. Or would its charge injection noise be too large
for this application?

Attila Kinali
--
It is upon moral qualities that a society is ultimately founded. All
the prosperity and technological sophistication in the world is of no
use without that foundation.
-- Miss Matheson, The Diamond Age, Neil Stephenson
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Attila Kinali
2018-07-07 16:31:47 UTC
Permalink
Moin,

On Sat, 24 Feb 2018 23:44:16 -0500
Post by Charles Steinmetz
Bert asked if the LT1793 is a good choice. I suggested the LT1012 as
superior in the specific parameters that will provide best performance
in the HP circuit
(https://www.febo.com/pipermail/time-nuts/2018-February/108964.html).
Attila suggested the LTC6240HV.
I continue to believe that the LT1012 is the best choice (or,
alternatively, the similar OP97 -- but the LT1012 would be my first choice).
As Attila noted, the 6240 is limited to +/- 5v supplies. I do not know
if the output voltage of the A9 ass'y needs to be able to swing beyond
+/- 5v, but I would not be inclined to change this without a lot of
careful thought (and adding another op-amp does not excite me). But
really, that is not necessary. Even if the 6240 could supply outputs up
to +/- 15v, the LT1012 would still be a better choice.
Coming back to an old thread...
While looking for a suitable opamp for another application, I stumbled
across the ADA4077. It is basically the modern equivalent of the LT1012.
All but the input bias current and input voltage range specs are better:

(worst case where available, typical else)

LT1012 ADA4077 (B grade)
Offset voltage 120µV 65µV
Offset tempco 1.5µV/°C 0.25µV/°C
Offset longterm 0.4µV/month 0.5µV/10kh (13months!)
Bias current 0.2nA 1.5nA
Noise voltage density 14nV/√Hz 7nV/√Hz
Low Freq Noise 0.5Vpp 0.25Vpp
GBW 0.8MHz 3.8MHz
Slew rate 0.2V/µs 1.2V/µs

The SO-8 packages are pin compatible, beside the missing offset compensation.

Unless you are using a chopper opamp for drift compensation, the ADA4077
might be worth considering. The higher GBW and slew rate would be benefitial
in an integrator application like the A9 board, as it improves linearity.

Attila Kinali
--
<JaberWorky> The bad part of Zurich is where the degenerates
throw DARK chocolate at you.

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Mark Sims
2018-02-25 02:35:47 UTC
Permalink
For a while, all makers of polycarbonate caps got out of the business. The US government had to step in and get involved... apparently they are used in a lot of explody thingies, etc.

Mouser shows one (around $7 for a 4.7 uF cap):
https://www.mouser.com/ProductDetail/Vishay-BC-Components/BFC234421475?qs=XPb5zkzE6%252bBS9mv3hRFZcw%3d%3d

But, the datasheet link goes to a resistor...
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Charles Steinmetz
2018-02-25 11:35:58 UTC
Permalink
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
Post by Mark Sims
For a while, all makers of polycarbonate caps got out of the business. The US government had to step in and get involved... apparently they are used in a lot of explody thingies, etc.
https://www.mouser.com/ProductDetail/Vishay-BC-Components/BFC234421475?qs=XPb5zkzE6%252bBS9mv3hRFZcw%3d%3d
But, the datasheet link goes to a resistor...
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Azelio Boriani
2018-02-25 12:46:07 UTC
Permalink
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
Post by Charles Steinmetz
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
Post by Mark Sims
For a while, all makers of polycarbonate caps got out of the business.
The US government had to step in and get involved... apparently they are
used in a lot of explody thingies, etc.
https://www.mouser.com/ProductDetail/Vishay-BC-Components/BFC234421475?qs=XPb5zkzE6%252bBS9mv3hRFZcw%3d%3d
But, the datasheet link goes to a resistor...
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Gerhard Hoffmann
2018-02-25 19:50:42 UTC
Permalink
Post by Azelio Boriani
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...
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


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paul swed
2018-02-26 21:23:15 UTC
Permalink
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
Post by Gerhard Hoffmann
Post by Azelio Boriani
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...
Why not go to Mouser or DK, as usual?
< 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
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Poul-Henning Kamp
2018-02-26 22:05:52 UTC
Permalink
--------
Post by paul swed
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
***@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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Wayne Holder
2018-02-26 22:36:00 UTC
Permalink
Post by Poul-Henning Kamp
Post by Poul-Henning Kamp
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
Post by Poul-Henning Kamp
--------
Post by Poul-Henning Kamp
I reverse engineered the system and guess what cap was bad? The
integrator.
Post by Poul-Henning Kamp
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
FreeBSD committer | BSD since 4.3-tahoe
Never attribute to malice what can adequately be explained by incompetence.
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Poul-Henning Kamp
2018-02-26 23:20:10 UTC
Permalink
--------
Post by Wayne Holder
Post by Poul-Henning Kamp
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.
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.
--
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Charles Steinmetz
2018-03-04 19:17:24 UTC
Permalink
Post by Poul-Henning Kamp
The input signal to the integrator is continuous and jump-free and
the relevant time constant is sub-second. Dielectric absorption
doesn't matter when there are no voltage jumps.
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


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Poul-Henning Kamp
2018-03-04 20:05:57 UTC
Permalink
--------
Post by Charles Steinmetz
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.
I fully agree, and if it were me, I would absolutely use the best
capacitor I could find at a non-insane price.

But that was exacly my point: The only thing you (might!) get by
spending an *insane* amount of money on that capacitor is PTFE and
its better dielectric absorption.

But there are three good reasons not to.

First, they are HUGE, typically a couple of inches in diameter and
four or five inches long[1]

Second, there are no reputable suppliers of ~5µF PTFE capacitors
that I have been able to find, there are only audiohomoeopaths.

*Nowhere* have I seen anybody buy an audiohomoepathy PTFE capacitor
and publish a traceable DA measurement for it, much less information
about tolerance, lot variations etc.

I am certainly not going to shell out $785.07 for what is claimed
to be a newly produced PTFE capacitor[2]:

https://www.v-cap.com/cutf-capacitors.php

Neither am I going to shell out $34.70 for something which may or
may not be USSR army surplus and which may or may not be PTFE[3].

https://www.ebay.co.uk/itm/Lot-of-1-piece-K72-11-Teflon-Capacitors-0-22uF-4-7uF-125V-1000V-NOS-Tested/132443841947?hash=item1ed644a59b:m:mPF1aOO4F7dJXTSF0qHKcSQ

And third, the difference in DA between PTFE and Polystyrene is
barely a factor five and it is from 0.05%(PS) to 0.01%(PTFE).

That is simply not going to make *any* difference in an HP5065A.

The trick here is to do the math on the S/N ratio of the optical
signal: The A9-capacitor is primarily a low-pass filter, and pretty
much any sane capacitor can do that.

Poul-Henning

[1] Almost any other type of capacitor is wound from two layers of
insulator on which a thin layer of metal has been deposited by
evaporation or sputtering. PTFE must be wound from two PTFE films
and two metal films, which means a lot more metal, because it must
have the mechanical strength for the winding operation.

[2] Notice the claimed "dielectric coefficient of 1.45" ? Either
he means "Dielectric Absorption" in which case the number is in %
and *horrible*, or he means "Dielectric Constant" in which case the
number is physically impossible.

[3] Because USSR wasn't very good at PTFE to begin with.
--
Poul-Henning Kamp | UNIX since Zilog Zeus 3.20
***@FreeBSD.ORG | TCP/IP since RFC 956
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Charles Steinmetz
2018-03-04 21:04:53 UTC
Permalink
Post by Poul-Henning Kamp
I fully agree, and if it were me, I would absolutely use the best
capacitor I could find at a non-insane price.
But that was exacly my point: The only thing you (might!) get by
spending an *insane* amount of money on that capacitor is PTFE and
its better dielectric absorption. * * *
And third, the difference in DA between PTFE and Polystyrene is
barely a factor five and it is from 0.05%(PS) to 0.01%(PTFE).
I agree, no PTFE (as I said in a previous message) because it is simply
impractible (or even impossible) to fit on a board that fits into the
5065A. But as I said in the same message, that is also true of PS
(also, I'm not aware of any currently available in integer uF values).

Last I knew, there are (were?) at least 3 reputable suppliers of PTFE
capacitors, but none of my designs in current production uses them so I
don't have any recent experience. I do see that Electrocube still lists
the 463D series on a web page with a 2018 copyright date.

I concur with everything you say about alleged PTFE caps from
"alternative" suppliers.

So, no PTFE or PS for practical reasons. That leaves us with PP, PPS,
and perhaps PC. These all have reasonably similar DA, so as long as one
checks the particular capacitor's datasheet to verify, DA should not be
much of a factor in choosing between them.

Best regards,

Charles


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Orin Eman
2018-03-04 22:43:41 UTC
Permalink
So, no PTFE or PS for practical reasons. That leaves us with PP, PPS, and
perhaps PC. These all have reasonably similar DA, so as long as one checks
the particular capacitor's datasheet to verify, DA should not be much of a
factor in choosing between them.
FWIW, WIMA are claiming 0.05% for their MKP 4 PP capacitors. They
performed about the same as the original integration capacitor in my 3455A
DMM - and about the same as some Polystyrene I found online somewhere - at
the time intervals that the 3455A uses.
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Bill Hawkins
2018-02-27 04:21:42 UTC
Permalink
Group,

After 40 years of doing PID control for industrial processes, I'm used
to an error tolerance of 10E-3. So I couldn't understand an integrator
with a 10 K resistor and a 5 mfd capacitor.

But this is time nuts, and the tolerance is more like 10E-13.

An integrator as a controller takes any deviation from zero error
voltage and moves the output in a direction that will return the error
to zero.

In this case, 10 K is the practical lower limit to the input resistor
for the desired time constant, with 5 mfd as a practical upper limit.
Any current flowing in that resistor changes the value of zero error,
which causes the output to move when the actual error is zero. This
makes the frequency wander. The current can come from the opamp bias or
capacitor leakage when the output is not zero.

Similarly, a change in the opamp zero offset causes a false error which
makes the output move when it shouldn't.

So I withdraw my comment about aluminum electrolytics, which was made
without a timenuts perspective.

Determining maximum error currents and offsets is simply a matter of
mathematics, which is left as an exercise for the student.

Regards,
Bill Hawkins

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Didier Juges
2018-03-05 12:11:29 UTC
Permalink
It depends on the quantity they buy. I just looked for X7R 0.1uF in 0805 at
Digikey and the automotive grade (10%, -55 to +125) is cheaper than the non
automotive grade with worse tolerance and more limited temperature range.
Next time you buy it may be reversed...
Post by Gerhard Hoffmann
Post by Azelio Boriani
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...
Why not go to Mouser or DK, as usual?
< 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
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Bill Hawkins
2018-02-25 03:26:07 UTC
Permalink
Corby

A time constant is calculated from R and C.

If 50 milliseconds is the correct number, R for 5 mfd is 10,000 ohms.

You could use an aluminum electrolytic for the capacitor.

Can you tell us where the 50 ms number came from?

Regards,
Bill Hawkins


-----Original Message-----
From: time-nuts [mailto:time-nuts-***@febo.com] On Behalf Of
***@juno.com
Sent: Saturday, February 24, 2018 5:45 PM
To: time-***@febo.com
Subject: [time-nuts] Replacement A9 boards for the HP 5065A

Hi,

I'm working to make some replacement A9 boards for the HP 5065A to the
new style schematic.

Will share the Gerber file when done.

The integrator capacitor is a 1986 vintage TRW 5.0ufd 50V 10%
.42"DX1.0"L axial.

Of course it has an HP part number and no manufactures #.

Any guess as to what type it is?

Polycarbonate, polypropylene, ???????

Just wanting to find a good modern replacement for its use. (Integrator
with a 50ms time constant.)

Thanks,

Corby

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ewkehren via time-nuts
2018-02-25 11:35:32 UTC
Permalink
Corby is still asleep, on the old board it was 0.5 uF and 100K now 5 uF and 10K. Who knows what HP knew in the 60`s but it works and I dought that it is critical. No where is there any fine  tuning like two resistors in seriesBert Kehren 

Sent from my Galaxy Tab® A
-------- Original message --------From: Bill Hawkins <***@pobox.com> Date: 2/24/18 10:26 PM (GMT-05:00) To: 'Discussion of precise time and frequency measurement' <time-***@febo.com> Subject: Re: [time-nuts] Replacement A9 boards for the HP 5065A
Corby

A time constant is calculated from R and C.

If 50 milliseconds is the correct number, R for 5 mfd is 10,000 ohms.

You could use an aluminum electrolytic for the capacitor.

Can you tell us where the 50 ms number came from?

Regards,
Bill Hawkins


-----Original Message-----
From: time-nuts [mailto:time-nuts-***@febo.com] On Behalf Of
***@juno.com
Sent: Saturday, February 24, 2018 5:45 PM
To: time-***@febo.com
Subject: [time-nuts] Replacement A9 boards for the HP 5065A

Hi,

I'm working to make some replacement A9 boards for the HP 5065A to the
new style schematic.

Will share the Gerber file when done.

The integrator capacitor is a 1986 vintage TRW 5.0ufd 50V 10%
.42"DX1.0"L axial.

Of course it has an HP part number and no manufactures #.

Any guess as to what type it is?

Polycarbonate, polypropylene, ???????

Just wanting to find a good modern replacement for its use. (Integrator
with a 50ms time constant.)

Thanks,

Corby

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ewkehren via time-nuts
2018-02-26 15:20:43 UTC
Permalink
We have decided to go with the 1012 do we need to do any thing with pin 5Bert kehren


Sent from my Galaxy Tab® A
-------- Original message --------From: Attila Kinali <***@kinali.ch> Date: 2/26/18 9:53 AM (GMT-05:00) To: Discussion of precise time and frequency measurement <time-***@febo.com> Subject: Re: [time-nuts] Replacement A9 boards for the HP 5065A
On Sat, 24 Feb 2018 23:44:16 -0500
Post by Charles Steinmetz
Given the relatively low resistances at the op-amp inputs (10k ohms),
the ultra-low input "bias" (leakage) current of the 6240 is simply
unnecessary.  Any offset due to the input currents (within the general
range of any of these op-amps) is insignificant compared to the op-amp's
offset voltage.  Thus, offset voltage, offset voltage tempco, and offset
voltage long-tem drift are the critical parameters (as Poul-Henning
pointed out).  And here, the 1012 is clearly the best of the three.  In
addition to having the lowest input offset spec, the 1012 has guaranteed
maximum specifications for these important parameters.  The 6240 (for
good reason) is *not even rated* for long-term stability (drift).
(Long-term offset stability is a particular weakness of CMOS op-amps.)
Oh.. right, I didn't think about long term behaviour. Thanks for the correction!

BTW: How about using an LTC2057 then? Its input bias current  and
GBW spec is similar to the LT1012, but its offset voltage and drift
are far superior. Or would its charge injection noise be too large
for this application?

Attila Kinali
--
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the prosperity and technological sophistication in the world is of no
use without that foundation.
                 -- Miss Matheson, The Diamond Age, Neil Stephenson
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