vintage tantalum capacitor replacement

[mongo]

I am having a hard time finding reliable information on the real value of replacing these.  I know that the 70's versions were fragile and would fail as a short but I am planning a major bit of maintenance on some vintage poly-synths and I would prefer to avoid replacing these if possible.

I am already going to replace all of the electrolytic as well as replacing all of the 4000-Series Chips with socketed modern versions but that is a far smaller number of items than the massive number of tantalum caps.

I will probably document all of the values as the schematics for these large vintage synths is quite sparse but as the number of VCOs, VCFs and VCAs is massive I am mostly worried that they binned these in matching values when they were built and that I will not have the budget to do the same.

But if there is a real concern I will do the work just so that I don't have to dig into them again.

As a side node only Vishay and Lelon seem to make axial electrolytic capacitors in the 10% tolerance range, but only for 500 hours in the sizes I need.  I have never used those brand and I think my normal axial brand Nichicon at 20% will be more stable over time but I would appreciate opinions.

I have never really had to plan for multi decade survivability before but I am doing both a Octave Plateau Voyetra 8 and an Oberheim ob-8 and would like to preserve them for as long as possible.

Thanks in advance.

[stj]

there is no value, failure is rare and usually caused by poor psu's effecting tants on a power rail.
i have never seen one fail in an audio path.

[mongo]

Thanks, it had a woo smell to it.

[stj]

they are dipped in resin. unless it shows signs of cooking i would ignore it.

[SeanB]

Why replace the working 4000 series devices, if they still work no need. Only change the dead ones, and if there are 2 or more with the same batch code that died then do all of those date code. Your replacement devices have much higher probability of either being dead from ESD damage or of being recycled and remarked fakes.

Only dipped tantalum capacitors on power rails had issues, and only there where they were used close to rated voltage. A 35V capacitor on a 5V rail almost never fails, but a 16V device on a 15V rail has a fair chance of popping, Replace with a regular 105C electrolytic, 20% tolerance is fine, and for a power rail you can go to the next higher capacitance and a higher voltage with very little issue, provided it will fit there. In any case a 100uF 63V 105C capacitor will replace any 10,22,47uF tantalum capacitor on a power rail with no problems, it will fit, and will have similar low ESR and a long life.

[mongo]

There are a few reasons.

The 6 micron RCA CD4000 and Motorola MC14000 series from the era have a reported metal migration issue so getting them into sockets will allow easier repairs in the future.

There are no known public schematics for the Voyetra 8 control lines and because they are simple two layer boards it will be easy to document when putting in sockets.

And while I am in there I can just replace these older chips with modern units for a very small amount of money and avoid the issues all together.

[dan3460]

In my experience tantalums depend on the year, I have had Tektronix equipment where almost all Tantalums are bad and I have had others, even older equipment, with all tantalums in top shape.
A couple of years ago I would do a shotgun replace of all tantalums, since then I have only been replacing what is bad. If I see that I had to replace two or three tantalums, I will do a shotgun replacement of all that I see.
 

[David Hess]

In my experience tantalums depend on the year, I have had Tektronix equipment where almost all Tantalums are bad and I have had others, even older equipment, with all tantalums in top shape.

A couple of years ago I would do a shotgun replace of all tantalums, since then I have only been replacing what is bad. If I see that I had to replace two or three tantalums, I will do a shotgun replacement of all that I see.

The early marketing and specifications for dipped solid tantalum capacitors touted them as not requiring voltage derating which Tektronix perhaps foolishly followed for a time.  All of the failures I have seen involved lack of voltage derating and I do the same thing; when I replace one, I check the others and replace them if they were not sufficiently voltage derated.

I have tracked down three different possible causes for the failures but they all involve thermal runaway of the self healing characteristic of these capacitors which is ameliorated by appropriate voltage derating.

Only dipped tantalum capacitors on power rails had issues, and only there where they were used close to rated voltage. A 35V capacitor on a 5V rail almost never fails, but a 16V device on a 15V rail has a fair chance of popping, Replace with a regular 105C electrolytic, 20% tolerance is fine, and for a power rail you can go to the next higher capacitance and a higher voltage with very little issue, provided it will fit there. In any case a 100uF 63V 105C capacitor will replace any 10,22,47uF tantalum capacitor on a power rail with no problems, it will fit, and will have similar low ESR and a long life.

When replacing solid tantalums I use roughly the same rule of thumb.  To get an equivalent ESR, an aluminum electrolytic capacitor will need about 2 to 4 times the capacitance.  This still will not yield as good of a performance at high frequencies but I have yet to see it be a problem.

Usually though I hit my local surplus electronics store and go through their bins for inexpensive NOS solid tantalum capacitors to use as replacements with appropriate voltage derating of course.  Since their origin is somewhat nebulous, I conduct my own burn in test as shown.

[Tantratron]

Few months ago, I had a failure on a tektronix PG506 and lately on a tektronix TG501.

Upon inspecting main root cause, the problem seems that main tantalum capacitor got shorted.

What is the best replacement strategy, technical choice wether full recap of tantalum capacitors or at minimum, replace for example these K100 20V and K100 10V capacitor in my TG501 (C640, C615 and C495 and C 496) or K47 25V and K15 20V in my PG506 (C170, C180, C1062 and C1065) ?

[David Hess]

I had several tantalum capacitor failures in my PG506.  After I replaced the first one, another shorted while I was watching it so I ended up replacing all of the solid tantalum capacitors on the 15 volt supplies.

Tektronix did not properly voltage derate solid tantalum capacitors in their instruments of that era so once there is a failure, I replace all of the solid tantalum capacitors operating at that voltage with new ones which have been voltage derated by 1/2 to 2/3rds, so I would use 25 volt capacitors on a 15 volt supply.  Alternatively, high frequency aluminum electrolytic capacitors of 2 to 4 times the capacitance can be used.

[Tantratron]

Hello David,

With my two PG506, it seems the failure concerns always the +/- 16.5V power rail bus (so circa +/- 15V). One failure on the main A1 board and another on the fast rise board.

With my TG501, same situation on the +15V where in the case, the A2 mixer board and main A1 board.

The +5V seems to better survive for some reasons but I could be wrong.

Ok now just to make sure I understand your recommendation if I go the route of stop using tantalum NOS and only replace by Nichicon electrolytics. Say I want to replace a K100-20V tantalum (+15Vdc bus), shall I replace by Nichicon 100uF of 50V or do you need to derate by 2 its capacitance as well (i.e. 200uF and 50V) ?

Albert

[gnuarm]

Why replace the working 4000 series devices, if they still work no need. Only change the dead ones, and if there are 2 or more with the same batch code that died then do all of those date code. Your replacement devices have much higher probability of either being dead from ESD damage or of being recycled and remarked fakes.

Only dipped tantalum capacitors on power rails had issues, and only there where they were used close to rated voltage. A 35V capacitor on a 5V rail almost never fails, but a 16V device on a 15V rail has a fair chance of popping, Replace with a regular 105C electrolytic, 20% tolerance is fine, and for a power rail you can go to the next higher capacitance and a higher voltage with very little issue, provided it will fit there. In any case a 100uF 63V 105C capacitor will replace any 10,22,47uF tantalum capacitor on a power rail with no problems, it will fit, and will have similar low ESR and a long life.

I used an epoxy coated tantalum in my design and have had a low, but significant failure rate at fabrication time.  Tantalum caps have can have tiny shorts that will self heal if given the time and the current restricted.  I don't recall the details, but they need to be brought up to voltage with current limiting.  After that they should be pretty reliable. 

I agree that most electronic components do not have a significant wear rate and will outlast the owner other than a few parts like electrolytic caps that have definite shelf lives. 

One caution about using overly large value caps in power circuits.  There is a surge current when applying voltage to caps.  The vintage equipment under discussion likely does not have a soft start on power up.  So these caps are given full voltage at startup with no current limiting.  That surge can be significant.  I'm working an issue right now where a set of six 1,000 uF caps are used.  On plugging in the battery a simulation shows over 200 amps peak!  I'm worried this will be a problem.  The caps have no rating for one time surge, but the rippled current is about an amp.  Heck, that surge exceeds the current rating for the power switch that selects the battery for the power source.

[gnuarm]

There are a few reasons.

The 6 micron RCA CD4000 and Motorola MC14000 series from the era have a reported metal migration issue so getting them into sockets will allow easier repairs in the future.

There are no known public schematics for the Voyetra 8 control lines and because they are simple two layer boards it will be easy to document when putting in sockets.

And while I am in there I can just replace these older chips with modern units for a very small amount of money and avoid the issues all together.

How is it easier to replace a part now rather than waiting for it to fail... if it fails?  Sockets themselves are a well known source of failure.  Connectors, sockets and switches should all be avoided for reliable equipment.

[gnuarm]

In my experience tantalums depend on the year, I have had Tektronix equipment where almost all Tantalums are bad and I have had others, even older equipment, with all tantalums in top shape.
A couple of years ago I would do a shotgun replace of all tantalums, since then I have only been replacing what is bad. If I see that I had to replace two or three tantalums, I will do a shotgun replacement of all that I see.

You are probably seeing design issues rather than date of manufacture.  I have no doubt there have been changes in reliability of tantalum caps.  Lord knows we've seen that plenty in electrolytic caps.  But to be associated with a line of equipment probably is associated with the design.  Tantalum caps have all manner of precautions and recommendations that must be observed for long life.

[gnuarm]

Hello David,

With my two PG506, it seems the failure concerns always the +/- 16.5V power rail bus (so circa +/- 15V). One failure on the main A1 board and another on the fast rise board.

With my TG501, same situation on the +15V where in the case, the A2 mixer board and main A1 board.

The +5V seems to better survive for some reasons but I could be wrong.

Ok now just to make sure I understand your recommendation if I go the route of stop using tantalum NOS and only replace by Nichicon electrolytics. Say I want to replace a K100-20V tantalum (+15Vdc bus), shall I replace by Nichicon 100uF of 50V or do you need to derate by 2 its capacitance as well (i.e. 200uF and 50V) ?

Albert

If the capacitors are not properly derated, they simply need to be replaced by components that are derated.  So for a 15 volt power rail a 100 uF should be replaced by a 100 uF, 35 volt tantalum.  It is hard for me to imagine replacing with an electrolytic cap as these have clearly stated, relatively short lifetimes.  Electrolytic caps are why most consumer electronics fails, especially anything that gets warm.  LED and CFL light bulbs are prime examples.  20,000 hours, not if you don't keep them cool!

[Tantratron]

Hello David,

With my two PG506, it seems the failure concerns always the +/- 16.5V power rail bus (so circa +/- 15V). One failure on the main A1 board and another on the fast rise board.

With my TG501, same situation on the +15V where in the case, the A2 mixer board and main A1 board.

The +5V seems to better survive for some reasons but I could be wrong.

Ok now just to make sure I understand your recommendation if I go the route of stop using tantalum NOS and only replace by Nichicon electrolytics. Say I want to replace a K100-20V tantalum (+15Vdc bus), shall I replace by Nichicon 100uF of 50V or do you need to derate by 2 its capacitance as well (i.e. 200uF and 50V) ?

Albert

If the capacitors are not properly derated, they simply need to be replaced by components that are derated.  So for a 15 volt power rail a 100 uF should be replaced by a 100 uF, 35 volt tantalum.  It is hard for me to imagine replacing with an electrolytic cap as these have clearly stated, relatively short lifetimes.  Electrolytic caps are why most consumer electronics fails, especially anything that gets warm.  LED and CFL light bulbs are prime examples.  20,000 hours, not if you don't keep them cool!

Thank your for this post and the previous ones where again I just remind another technical point on these vintage tektronix TM500 sections. One topic is the form size factor where I understand visually that most of these tantalum power rails are very small versus their capacitance.

I can make some close view pictures of my two tektronix boards, you'll see there is not much room left to solder safely wether a new derated tantalum or electrolytic. So here the problem is the physical left room on these old PCB's versus the new uF/mm3 ratio.

Say we look on digikey, mouser, farnell... what new tantalum would you recommend as a choice, for example replacing and old K100-20V by say a new 100uF-35V ?

[gnuarm]

Say we look on digikey, mouser, farnell... what new tantalum would you recommend as a choice, for example replacing and old K100-20V by say a new 100uF-35V ?

I honestly don't understand the question.  Or I should say I don't understand how I could answer the question.  As you say, the original part has a form factor which you have not shared that I am aware of.  A replacement would need to match that.  In the intervening years I expect the density of tantalum caps has improved.  I know they continue to improve in ceramic caps. 

If there is not a higher voltage part in the same package as you are replacing, you will need to find a package with a larger volume that is potentially compatible since you will be hand soldering I expect.  I don't even know if these are surface mount.  Do they have leaded tantalum caps?

Digikey has very good info on caps.  You are going to have to do your due diligence. 

[Tantratron]

Say we look on digikey, mouser, farnell... what new tantalum would you recommend as a choice, for example replacing and old K100-20V by say a new 100uF-35V ?

I honestly don't understand the question.  Or I should say I don't understand how I could answer the question.  As you say, the original part has a form factor which you have not shared that I am aware of.  A replacement would need to match that.  In the intervening years I expect the density of tantalum caps has improved.  I know they continue to improve in ceramic caps. 

If there is not a higher voltage part in the same package as you are replacing, you will need to find a package with a larger volume that is potentially compatible since you will be hand soldering I expect.  I don't even know if these are surface mount.  Do they have leaded tantalum caps?

Digikey has very good info on caps.  You are going to have to do your due diligence.

This thread is general tantalum vintage (many products) then some of us discuss the specific case of tektronix TM500, in particular these two sections PG506 https://w140.com/tekwiki/wiki/PG506 and TG501 https://w140.com/tekwiki/wiki/TG501. If you really want, I can zoom and show you which specific tantalum replacement is a form-size replacement issue

In the 1970's there were probably no surface mounts and my question was simple except I do not speak english as native language.

So the real topic is to find out if R&D, innovation offers a reduction of size in tantalum cap... same capacitance, same voltage then does the cap smaller ?

If yes then great where we solve the tektronix initial design issue by replacing with a higher voltage rating the same capacitance, same volume. Otherwise problem then no choice go electrolytic with risk of quick failure as you noted.

Higher voltage - same capacitance then can we buy new tantalum being smaller volume that its equivalent legacy in the 70's or 80's for ease of through soldering.

Voila

[gnuarm]

I did a search on through hole tantalum caps and yes, they are made.  I remember them now.  I had used them many years ago, but had forgotten.  Since you need a through hole part, the exact form factor is not important.  Leads can be inserted into the holes on your board by bending the leads to the appropriate spacing is required. 

So I don't see a problem with the form factor.  There is still the issue of needing to bring up the voltage with current limiting the first time.  You may want to construct a jig with a resistor in series with the cap applying the rated voltage or at least the voltage they will be used with in the circuit. 

[Tantratron]

One caution about using overly large value caps in power circuits.  There is a surge current when applying voltage to caps.  The vintage equipment under discussion likely does not have a soft start on power up.  So these caps are given full voltage at startup with no current limiting.  That surge can be significant.  I'm working an issue right now where a set of six 1,000 uF caps are used.  On plugging in the battery a simulation shows over 200 amps peak!  I'm worried this will be a problem.  The caps have no rating for one time surge, but the rippled current is about an amp.  Heck, that surge exceeds the current rating for the power switch that selects the battery for the power source.

This is a very valid good point where in the hypothesis to replace old legacy tantalum by electrolytic (same voltage but higher capacitance), there must be a tradeoff to not surge destroy the primary part of the tektronix TM500 section power supply.

To be or not to be... either modern tantalum through holes caps have same form factor where we increase their voltage rating (same capacitance) or we increase capacitance-voltage of electrolytic but then risk of your wisdom observation

[Kleinstein]

When replacing tantalum caps with aluminum ones, keep in mind that the ESR depends on temperature. This especially gets a problem for low temperature where the ESR goes up.

For the modern Al electrolytic caps there are also 3 types:  classical ones with high ESR, low ESR and polymer caps. For lowest ESR Ta cap replacement it would be mainly the low ESR or polymer type.

In a linear power supply often a very low ESR value is no needed and not even desirable.

The tantalum caps are usually relatively small, so I would not worry so much about inrush current. With changed capacity a possible problem could be the time it needs for the supply to come up and the may change the sequence. Slightly higher ESR may be the lesser evil compared to more capacitance.

It depends on the circuit - so ideally one pics a suitable cap based on the circuit, not so much on the old cap that was in there. In some places a higher capacitance is actually desirable and was just not available at the time.
In rare cases tantalum caps were also used for signal filtering, oscillators or delays.

[Zero999]

I've never had any problems with solid tantalum capacitors, which are properly voltage de-rated. I certainly wouldn't recommed replacing them with aluminium capacitors, which will have a higher ESR and probably won't last as long, as they tend to dry up, especially at high temperatures.

Solid tantalum capacitors don't dry up and have a low ESR. Replace them only if they're defective, or if it's obvious they're inadequately rated, in which case just choose a tantalum, with a higher voltage rating.

[gnuarm]

What voltage rating is required?  I've heard to derate them by 50%.  I've heard 60%.  None of that resolves the issue of infant mortality from the micro shorts.  I did some research into this and the tantalum makers recommend initial power to be applied with a current limit to allow the micro shorts to self heal (or burn out or whatever they do) without overloading the cap with a major current surge through the short.

I think it was Kemet who had the best white papers on this topic.  The fact that you haven't seen a problem doesn't mean it doesn't exist.  It means you just have not designed a circuit that was a challenge to the cap.  Do you know what parameters that you designed right?

[rsjsouza]

As a side node only Vishay and Lelon seem to make axial electrolytic capacitors in the 10% tolerance range, but only for 500 hours in the sizes I need.  I have never used those brand and I think my normal axial brand Nichicon at 20% will be more stable over time but I would appreciate opinions.

I would instead focus on the much wider availability and features of the radial variants. Sure, their overtwisted legs do not look as beautiful but you can get parts with much larger life span and usually lower cost. Just make sure you don't twist the lead too close to the device's body and all is well. An example is shown at my repair of an old calculator Casio AS-A

Just like others, I also think that shotgun replacement of the CD4k devices is a bit overkill. The amount of fully functioning vintage equipment with them is quite high. Also, for a portable equipment the sockets can be a problem, but be sure to get something from a reputable manufacturer, as endurance testing and mechanical tolerances will be better. All sockets can potentially show some mechanical trouble over the years, but the machined pins with inner springs tend to fare better than the press fit ones. Details at:
https://www.te.com/usa-en/products/connectors/sockets/ic-sockets/dip-sockets.html?tab=pgp-story

I have never really had to plan for multi decade survivability before but I am doing both a Octave Plateau Voyetra 8 and an Oberheim ob-8 and would like to preserve them for as long as possible.

I don't know the Octave, but the Oberheim is a beautiful synth. Congratulations!

[David Hess]

Ok now just to make sure I understand your recommendation if I go the route of stop using tantalum NOS and only replace by Nichicon electrolytics. Say I want to replace a K100-20V tantalum (+15Vdc bus), shall I replace by Nichicon 100uF of 50V or do you need to derate by 2 its capacitance as well (i.e. 200uF and 50V) ?

To get a comparable impedance at high frequencies, an aluminum electrolytic capacitor needs to have like 4 times the capacitance of the solid tantalum capacitor it replaces.  This is often reflected in old application notes which will recommend a 1 microfarad tantalum capacitor or 10 microfarad aluminum electrolytic.