Replace tantalum caps with aluminum?

W

Walter Harley

Guest
I'm replacing the electrolytics in a nearly-40-year-old HP 654A test
oscillator. This is a 10Hz to 10MHz sinewave oscillator. I have the
service manual and schematics for it.

Many of the caps are specified in the service manual to be tantalum. Some
are quite large values, up to 390uF. The caps are all axial (cylinders with
leads at each end), which is a relatively uncommon package these days.

Can I replace these large-value tantalum caps with aluminum caps? I'm
thinking that in 1967, the ESR, tolerance, and stability of aluminum was
pretty lousy, but maybe now it's as good as tantalum was back then?

Thanks for any input.
 
In article <vspni5c6bsge57@corp.supernews.com>,
"Walter Harley" <walterh@cafewalterNOSPAM.com> wrote:

I'm replacing the electrolytics in a nearly-40-year-old HP 654A test
oscillator. This is a 10Hz to 10MHz sinewave oscillator. I have the
service manual and schematics for it.

Many of the caps are specified in the service manual to be tantalum. Some
are quite large values, up to 390uF. The caps are all axial (cylinders with
leads at each end), which is a relatively uncommon package these days.

Can I replace these large-value tantalum caps with aluminum caps? I'm
thinking that in 1967, the ESR, tolerance, and stability of aluminum was
pretty lousy, but maybe now it's as good as tantalum was back then?
Click to expand...
Check the operating temperatures. The tantalums may have a higher
operating range.

Tantalums are also made from slugs. Aluminum electrolytics tend to be
wound; they may have some peculiar resonances.

Al

--
There's never enough time to do it right the first time.......
 
"Al" <no.spam@here.com> wrote in message
news:no.spam-60DEB6.14292702122003@news.verizon.net...
Check the operating temperatures. The tantalums may have a higher
operating range.
Click to expand...
It's a low power device; basically sits pretty close to room temp.

Tantalums are also made from slugs. Aluminum electrolytics tend to be
wound; they may have some peculiar resonances.
Click to expand...
Hmm. I'll take a look at the mfr spec sheets for the aluminums. Thanks.
 
In sci.electronics.equipment Walter Harley <walterh@cafewalternospam.com> wrote:
I'm replacing the electrolytics in a nearly-40-year-old HP 654A test
oscillator. This is a 10Hz to 10MHz sinewave oscillator. I have the
service manual and schematics for it.

Many of the caps are specified in the service manual to be tantalum. Some
are quite large values, up to 390uF. The caps are all axial (cylinders with
leads at each end), which is a relatively uncommon package these days.

Can I replace these large-value tantalum caps with aluminum caps? I'm
thinking that in 1967, the ESR, tolerance, and stability of aluminum was
pretty lousy, but maybe now it's as good as tantalum was back then?
Click to expand...
If they are mostly working, you might measure the ESR now, and get an
idea.
 
"Walter Harley" <walterh@cafewalterNOSPAM.com> wrote in
news:vsprkpgagtl30@corp.supernews.com:

"Al" <no.spam@here.com> wrote in message
news:no.spam-60DEB6.14292702122003@news.verizon.net...
Check the operating temperatures. The tantalums may have a higher
operating range.

It's a low power device; basically sits pretty close to room temp.

Tantalums are also made from slugs. Aluminum electrolytics tend to be
wound; they may have some peculiar resonances.

Hmm. I'll take a look at the mfr spec sheets for the aluminums. Thanks.
Click to expand...
I suspect good low-ESR al. caps would work fine,and be much less expensive.

--
Jim Yanik,NRA member
jyanik-at-kua.net
 
"Jim Yanik" <jyanik@abuse.gov> wrote in message
news:Xns9445C9E0DBA7Bjyanikkuanet@204.117.192.21...
"Walter Harley" <walterh@cafewalterNOSPAM.com> wrote in
news:vsprkpgagtl30@corp.supernews.com:

"Al" <no.spam@here.com> wrote in message
news:no.spam-60DEB6.14292702122003@news.verizon.net...
Check the operating temperatures. The tantalums may have a higher
operating range.

It's a low power device; basically sits pretty close to room temp.

Tantalums are also made from slugs. Aluminum electrolytics tend to be
wound; they may have some peculiar resonances.

Hmm. I'll take a look at the mfr spec sheets for the aluminums.
Thanks.



I suspect good low-ESR al. caps would work fine,and be much less
expensive.

--
Jim Yanik,NRA member
jyanik-at-kua.net
Click to expand...

May also be worth checking out the "Solid Aluminium" caps. These are
different from the aluminium electrolytics. They have very low ESR
(comparable to tantalums) and very long life.

Costas
 
Have you checked www.mouser.com?


"Walter Harley" <walterh@cafewalterNOSPAM.com> wrote in
news:vspni5c6bsge57@corp.supernews.com:

I'm replacing the electrolytics in a nearly-40-year-old HP 654A test
oscillator. This is a 10Hz to 10MHz sinewave oscillator. I have the
service manual and schematics for it.

Many of the caps are specified in the service manual to be tantalum.
Some are quite large values, up to 390uF. The caps are all axial
(cylinders with leads at each end), which is a relatively uncommon
package these days.

Can I replace these large-value tantalum caps with aluminum caps? I'm
thinking that in 1967, the ESR, tolerance, and stability of aluminum
was pretty lousy, but maybe now it's as good as tantalum was back
then?

Thanks for any input.
Click to expand...
 
On Tue, 2 Dec 2003 10:47:32 -0800 "Walter Harley"
<walterh@cafewalterNOSPAM.com> wrote:

I'm replacing the electrolytics in a nearly-40-year-old HP 654A test
oscillator. This is a 10Hz to 10MHz sinewave oscillator. I have the
service manual and schematics for it.

Many of the caps are specified in the service manual to be tantalum. Some
are quite large values, up to 390uF. The caps are all axial (cylinders with
leads at each end), which is a relatively uncommon package these days.
Click to expand...
If these are in the metal cans with the glass seal around the positive
lead, then these tend to be VERY reliable and I would not replace them
with aluminums under any circumstances. They are quite pricey, but if
you should actually have a bad one, you should replace it with another
tantalum.

These are a much better cap than the teardrop tantalums.

I've actually never seen one of these good tantalum caps fail, but
I've increased the reliability of a lot of my gear by replacing failed
(and commonly failing) low voltage alum electrolytics with these. If
you keep your eyes open you can often get good deals on these at swap
meets. I've been picking them up for years and now have a good supply
whenever I need one.

-
-----------------------------------------------
Jim Adney jadney@vwtype3.org
Madison, WI 53711 USA
-----------------------------------------------
 
Electrolytics can have low lifetime specifications. I once saw a some with a
spec of only 1000 hours. Thats about 41 days! Must have been a mistake?
 
CWatters wrote:
Electrolytics can have low lifetime specifications. I once saw a some with a
spec of only 1000 hours. Thats about 41 days! Must have been a mistake?
Click to expand...
No, just cheap caps. You need to select electrolytics with a higher
temperature rating to get a longer life. In other words, the closer you
run it to its rated temperature, the quicker it fails. Cheap caps are
rated to 85°C, better caps are 125°C. You have to consider the operating
temp of the equipment, plus the heat generated by any AC passing though
the cap. A low ESR cap will generate less heat and last longer. Both
higher temperature grade and low ESR cost more money, so lots of bean
counters use the cheapest piece of crap they can sweep off the floor at
the factory.
--
22 days!


Michael A. Terrell
Central Florida
 
"CWatters" <colin.watters@pandoraBOX.be> wrote in message
news:Zbjzb.57778$mZ5.2007110@phobos.telenet-ops.be...
Electrolytics can have low lifetime specifications. I once saw a some with
a
spec of only 1000 hours. Thats about 41 days! Must have been a mistake?
Click to expand...
I believe I've read that lifetime doubles for each 10C under the rated temp.
So if they were 1000 hours at 85C, then when run at 25C they'd be good for
64k hours. That's 7.5 years of continuous operation.

So they probably put them in TV motherboards at 35C, and then the TV dies
after 3 years and the owner buys a new one. The cap not only saves you
money, it *earns* you money!
 
This has to be a mistake. Can you think of the hundreds of electro-caps
used in each of every TV set and appliance???

--

Greetings,

Jerry Greenberg GLG Technologies GLG
=========================================
WebPage http://www.zoom-one.com
Electronics http://www.zoom-one.com/electron.htm
=========================================


"CWatters" <colin.watters@pandoraBOX.be> wrote in message
news:Zbjzb.57778$mZ5.2007110@phobos.telenet-ops.be...
Electrolytics can have low lifetime specifications. I once saw a some with a
spec of only 1000 hours. Thats about 41 days! Must have been a mistake?
 
"Jerry G." <jerryg50@hotmail.com> wrote in
news:bql6qt$nuk$4@news.eusc.inter.net:

This has to be a mistake. Can you think of the hundreds of electro-caps
used in each of every TV set and appliance???
Click to expand...
Look thru the Digi-Key catalog,the list the typical life of some of their
electrolytics.I think that's a worst-case spec though.


--
Jim Yanik,NRA member
jyanik-at-kua.net
 
Hi Jerry,
No mistake but the rated life is done in hours over time
at a given temp for so much change in value at a max.
If ran that way most would still work longer if the circuit
allows it but it would be a poor choice to use in that case.
Jeff

"Jerry G." <jerryg50@hotmail.com> wrote in message
news:bql6qt$nuk$4@news.eusc.inter.net...
This has to be a mistake. Can you think of the hundreds of electro-caps
used in each of every TV set and appliance???

--

Greetings,

Jerry Greenberg GLG Technologies GLG
=========================================
WebPage http://www.zoom-one.com
Electronics http://www.zoom-one.com/electron.htm
=========================================


"CWatters" <colin.watters@pandoraBOX.be> wrote in message
news:Zbjzb.57778$mZ5.2007110@phobos.telenet-ops.be...
Electrolytics can have low lifetime specifications. I once saw a some with
a
spec of only 1000 hours. Thats about 41 days! Must have been a mistake?
Click to expand...
 
On 3 Dec 2003 17:16:42 GMT, "Walter Harley" <walterh@cafewalterNOSPAM.com>
wrote:

"CWatters" <colin.watters@pandoraBOX.be> wrote in message
news:Zbjzb.57778$mZ5.2007110@phobos.telenet-ops.be...
Electrolytics can have low lifetime specifications. I once saw a some with
a
spec of only 1000 hours. Thats about 41 days! Must have been a mistake?

I believe I've read that lifetime doubles for each 10C under the rated temp.
So if they were 1000 hours at 85C, then when run at 25C they'd be good for
64k hours. That's 7.5 years of continuous operation.

So they probably put them in TV motherboards at 35C, and then the TV dies
after 3 years and the owner buys a new one. The cap not only saves you
money, it *earns* you money!
Click to expand...
Only if the customer is stupid enough to buy your brand again.

--

Boris Mohar
 
On Wed, 03 Dec 2003 10:48:25 GMT, "CWatters" <colin.watters@pandoraBOX.be>
wrote:

Electrolytics can have low lifetime specifications. I once saw a some with a
spec of only 1000 hours. Thats about 41 days! Must have been a mistake?
Click to expand...
There is bit more to it.

http://www.illcap.com/LifeCalculator.asp



Regards,

Boris Mohar

Got Knock? - see:
Viatrack Printed Circuit Designs http://www3.sympatico.ca/borism/
Aurora, Ontario
 
"Boris Mohar" <borism@sympatico.ca> wrote in message
news:46tssv0275t8ar40ofuvmaviugkhor9ct8@4ax.com...
So they probably put them in TV motherboards at 35C, and then the TV dies
after 3 years and the owner buys a new one. The cap not only saves you
money, it *earns* you money!


Only if the customer is stupid enough to buy your brand again.
Click to expand...
....Unless the customer figures that all the other brands suck just as much.

Far as I can tell, practically everything out there these days is made to
the same low standards. It all seems to be a race to pinch every last $0.01
out of the retail cost, regardless of whether it halves the useful life of
the device, makes it less usable, or what. Except for "audiophile" audio
gear, which is just as absurd in the opposite direction.

That's part of why I'm fixing the old HP 654A that triggered this thread -
because it was built to be fixed, and to work and last a good long time. I
could buy some new Chinese-crap-factory test oscillator for less than the
time to fix the HP is going to cost me, but I don't wanna.

(Sorry to offend any Chinese engineers out there. I'm sure there are
companies in China making superb, high-quality, reliable, robust products.
Unfortunately, there don't seem to be any USA companies that want to import
them.)
 
On Wed, 3 Dec 2003 17:34:17 -0800, "Walter Harley"
<walterh@cafewalterNOSPAM.com> wrote:

That's part of why I'm fixing the old HP 654A that triggered this thread -
because it was built to be fixed, and to work and last a good long time. I
could buy some new Chinese-crap-factory test oscillator for less than the
time to fix the HP is going to cost me, but I don't wanna.
Click to expand...
Are those HP tantalums bad? You would be surprised how long tantalums last if
not abused.

--

Boris Mohar
 
"Boris Mohar" <borism@sympatico.ca> wrote in message
news:in4tsv0e1la66du9220t3m1dvikrv4idjq@4ax.com...
Are those HP tantalums bad? You would be surprised how long tantalums
last if
not abused.
Click to expand...

This morning I measured their ESR, and they all seemed fine, though one or
two have a bunch of crystallization around the terminals.

Is that the definitive test? Is there a better test? (I suppose I should
also measure their capacitance, which I've not yet done.)

-w
 
In the military world, we treat reliability extremely seriously. We use
Tantalum for most of the high C applications.

There is an attempt to cut the price of military electronics by using
commercial off the shelf components (COTS), but the reliability is not
there. Apart from electrolytics drying out, we have issues with plastic
packaged ICs which are hygroscopic, and even the in-built tendency of
semiconductors to die after a few year due to diffusion of the metalization
through the Silicon, and the migration of the metal across the surface of
the die.

In summary, the electrolytics are just one of the components which, for
consumer level electronics, tend to die more often than we would like, but
believe me, you do not want to incur the cost of going high reliability on
your next television.

Cheers,

Bill

"Jim Adney" <jadney@vwtype3.org> wrote in message
news:rdsqsv8lmsa296c2431315rispi1ebd3em@4ax.com...
On Tue, 2 Dec 2003 10:47:32 -0800 "Walter Harley"
walterh@cafewalterNOSPAM.com> wrote:

I'm replacing the electrolytics in a nearly-40-year-old HP 654A test
oscillator. This is a 10Hz to 10MHz sinewave oscillator. I have the
service manual and schematics for it.

Many of the caps are specified in the service manual to be tantalum.
Some
are quite large values, up to 390uF. The caps are all axial (cylinders
with
leads at each end), which is a relatively uncommon package these days.

If these are in the metal cans with the glass seal around the positive
lead, then these tend to be VERY reliable and I would not replace them
with aluminums under any circumstances. They are quite pricey, but if
you should actually have a bad one, you should replace it with another
tantalum.

These are a much better cap than the teardrop tantalums.

I've actually never seen one of these good tantalum caps fail, but
I've increased the reliability of a lot of my gear by replacing failed
(and commonly failing) low voltage alum electrolytics with these. If
you keep your eyes open you can often get good deals on these at swap
meets. I've been picking them up for years and now have a good supply
whenever I need one.

-
-----------------------------------------------
Jim Adney jadney@vwtype3.org
Madison, WI 53711 USA
-----------------------------------------------
Click to expand...
 
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