UK Vintage Radio Repair and Restoration Powered By Google Custom Search Vintage Radio and TV Service Data

Go Back   UK Vintage Radio Repair and Restoration Discussion Forum > General Vintage Technology > Components and Circuits

Notices

Components and Circuits For discussions about component types, alternatives and availability, circuit configurations and modifications etc. Discussions here should be of a general nature and not about specific sets.

Reply
 
Thread Tools
Old 22nd Apr 2024, 6:07 pm   #21
knobtwiddler
Octode
 
Join Date: Mar 2016
Location: London, UK.
Posts: 1,071
Default Re: Tantalum vs. electrolytic capacitor

Quote:
Originally Posted by Cruisin Marine View Post
The word tantalum sends me in to a shaking state of frenzy. Seen far too many bad one's to ever trust them in the slightest.
Ditto here. If they fail across power rails, they can cause serious damage. In signal coupling applications, they can sow confusion by passing DC into places where you don't expect to see it, potentially making one bark up a lot of wrong trees. I once saw an output amp in a control amp have a shorted tant that coupled its input. It had an Al electrolytic across the O/P that blocked DC. However, the SC tant enabled DC to get across the pot that fed the last stage. This meant that whenever the owner swept the pot it fed DC into the final stage that evaded the final cap, due to its ramping nature. All the other caps had been changed, but the owner was perplexed that sweeping the pot would trigger his amp's DC protection...
knobtwiddler is offline   Reply With Quote
Old 22nd Apr 2024, 6:20 pm   #22
G6Tanuki
Dekatron
 
G6Tanuki's Avatar
 
Join Date: Apr 2012
Location: Wiltshire, UK.
Posts: 14,139
Default Re: Tantalum vs. electrolytic capacitor

Tantalum capacitors were sold as a sort of 'magic bullet' to designers in the Sixties and Seventies, because they got loads of low-ESR capacitance into a very small physical volume.

They were not cheap though, so never really caught on in generic consumer electronics, though the likes of the Military got a good dose of the things in their electronics.

Fifty years later, their problems are coming home to roost. Clansman radios being the case I am most familiar with, thankfully modern aluminium etched foil electrolytics are available and if you choose a good brand (Panasonic, Rubycon) and avoid fakes, they are the obvious answer to a Tantalum Tantrum capacitor.
__________________
I'm the Operator of my Pocket Calculator. -Kraftwerk.
G6Tanuki is offline   Reply With Quote
Old 22nd Apr 2024, 7:31 pm   #23
Jan Zodiac
Hexode
 
Join Date: Sep 2021
Location: Aabenraa, South Jutland, Denmark.
Posts: 250
Default Re: Tantalum vs. electrolytic capacitor

Thanks. I will definetely choose the aluminium electrolytics over tantalums. And there is still a fair amount of axial types on Mouser, Digikey etc., that comes close to the original values.

Bang & Olufsen also had a period in the 70's where tantalums were spread all over their products. Those, and then the red/orange/grey ROE/ERO electrolytics in plastic housings.

I once got a really cool Grundig CN 1000 HiFi cassette deck from a friend. I thought it looked so cool and well build. It had problems with the logic control of the different functions. When I opened it, it was filled to the brim with tantalum drops. I quickly closed it again...

Jan
Jan Zodiac is offline   Reply With Quote
Old 22nd Apr 2024, 9:17 pm   #24
factory
Octode
 
Join Date: Jul 2009
Location: Cheshire, UK.
Posts: 1,782
Default Re: Tantalum vs. electrolytic capacitor

Thanks for reminding me of Grundig, they put on quite a good smoke & fire show, had to be C13 too.

Click image for larger version

Name:	DSC_2520a.jpg
Views:	135
Size:	74.6 KB
ID:	296742 Click image for larger version

Name:	DSC_2528a.jpg
Views:	134
Size:	79.5 KB
ID:	296743 Click image for larger version

Name:	DSC_2523a.jpg
Views:	133
Size:	103.7 KB
ID:	296744

Pictures are from a VG1000 TV pattern generator.

David
factory is offline   Reply With Quote
Old 22nd Apr 2024, 9:37 pm   #25
Philips210
Nonode
 
Join Date: May 2007
Location: Redruth, Cornwall, UK.
Posts: 2,633
Default Re: Tantalum vs. electrolytic capacitor

Tant beads for supply filtering are not to be trusted in my experience although they should be fine in low voltage timing circuits where they're operating well within their voltage rating. Perhaps the manufacturers could devise a self fusing mechanism to avoid the conflagration.

I expect top quality low leakage electrolytic caps will be fine as replacements in most cases.

Regards,
Symon
Philips210 is offline   Reply With Quote
Old 22nd Apr 2024, 10:40 pm   #26
Ted Kendall
Dekatron
 
Join Date: Jul 2008
Location: Kington, Herefordshire, UK.
Posts: 3,716
Default Re: Tantalum vs. electrolytic capacitor

It's a toss-up between these and RIFA paper jobs as to which smells worse...
Ted Kendall is offline   Reply With Quote
Old 22nd Apr 2024, 11:02 pm   #27
Craig Sawyers
Dekatron
 
Craig Sawyers's Avatar
 
Join Date: Nov 2010
Location: Oxford, UK.
Posts: 5,089
Default Re: Tantalum vs. electrolytic capacitor

Back in the day in my first job, I designed lots of semi mil spec gear. The manufacturer's technical notes extolled the virtues of their tantalum bead capacitors for supply filtering. They made 6V ones for 5V rails, 16V ones for +/-15V etc.

Back in the early/mid 80's, so 40+ years ago.

Of course, if the gear is still in use, the little burning timebombs will be ticking big time.

In fairness, all I and others (like Tektronix of that era) did was follow the apps notes.

Craig
__________________
Doomed for a certain term to walk the night
Craig Sawyers is offline   Reply With Quote
Old 23rd Apr 2024, 12:34 am   #28
knobtwiddler
Octode
 
Join Date: Mar 2016
Location: London, UK.
Posts: 1,071
Default Re: Tantalum vs. electrolytic capacitor

Some Al electrolytics can go up in flames under certain circumstances as well - not just tants. The trouble with tants is that once they've ignited, they stay that way and don't extinguish easily. Aside from obvious safety concerns, a serious worry is for multi-layer PCBs that might have high density logic tracking. If a flaming cap manages to burn into the PCB, it can be very difficult, if not impossible, to bridge the damaged tracks as a repair. I speak from bitter experience.
knobtwiddler is offline   Reply With Quote
Old 23rd Apr 2024, 11:54 am   #29
ppalped
Pentode
 
ppalped's Avatar
 
Join Date: Aug 2023
Location: Lisbon, Portugal.
Posts: 106
Default Re: Tantalum vs. electrolytic capacitor

Tantalum capacitors still have their uses and, in my opinion, their reliability is not as bad as it is usually painted, if they do not operate too close to their maximum voltage rating.

A good rule of thumb is to double (or triple) the Vrating, meaning that if the capacitor will operate at 15V, then use a 35V - of course this kind of defeats one of the reasons why they became so popular: size. Another good reason why they are still being used is their excellent stability, both in temperature and frequency variations.

Most of the tantalum caps that I've seen failing in older equipment in spectacular ways were operating very close to their maximum ratings - I usually replace them with another tantalum, but doubling the voltage rating (at least).

Also, personally I wouldn't use a tantalum as a DC blocker, in any situation. Polypropylene are my first choice for these use cases.

Alex
ppalped is offline   Reply With Quote
Old 23rd Apr 2024, 12:29 pm   #30
turretslug
Dekatron
 
turretslug's Avatar
 
Join Date: Nov 2011
Location: Surrey, UK.
Posts: 4,421
Default Re: Tantalum vs. electrolytic capacitor

Back in the day, I used to work on quite a bit of Philips professional kit and became familiar with Philips solid aluminium capacitors, similar applications to tantalum bead types (broadband coupling/decoupling, low leakage, good capacitance/volume ratio). They have orange epoxy-dip cases, similar-looking but flatter than the rounded tantalum bead types. I don't think I ever encountered a single duff one, quite unlike tantalum beads.... I thought the latter were about as welcome on a circuit board as ticks on a dog, and not dissimilar in appearance.

The Philips solid aluminium caps used to be available from the familiar suppliers (certainly Farnell) but were discontinued a while back, perhaps the general improvement in the characteristics of "conventional" aluminium foil electrolytics made them uncompetitive, though they were notably cheaper than tantalum beads in their time.
turretslug is offline   Reply With Quote
Old 23rd Apr 2024, 6:11 pm   #31
Leon Crampin
Octode
 
Join Date: Nov 2005
Location: Surrey, UK.
Posts: 1,894
Default Re: Tantalum vs. electrolytic capacitor

I never approved any tantalum capacitors for use by the automotive electronics company I worked for. The main problem with tants is, I think an excess hot spot current when subjected to even moderately high values of dv/dt which can occur when connected to low impedance sources, such as regulated power supplies.

So, a need for similarly sized components arose for use in a starting aid timer. The Philips orange bead solid Al devices met this requirement perfectly, without any significant failures.

Leon.
Leon Crampin is online now   Reply With Quote
Old 25th Apr 2024, 5:31 pm   #32
John_BS
Octode
 
John_BS's Avatar
 
Join Date: Dec 2008
Location: Wincanton, Somerset, UK.
Posts: 1,792
Default Re: Tantalum vs. electrolytic capacitor

I'll second Leon's comments.
I recall we were sent a note back in the 80's (as designers) cautioning that tants don't like very high dV/dT (i.e. current pulse), and that they were perfectly OK provided you didn't use them to decouple HT lines & similar capable of delivering more than an amp or so. Especially true with any kind of plug-in module where the DC power might be applied instantaneously. They were generally low esr and happy to run at 0V (these are solid tants).
John_BS is offline   Reply With Quote
Old 25th Apr 2024, 7:15 pm   #33
Maarten
Dekatron
 
Join Date: Dec 2007
Location: Haarlem, Netherlands
Posts: 4,260
Default Re: Tantalum vs. electrolytic capacitor

In my limited experience, tantalum beads are 'sort of OK' but certainly not 'perfectly OK' in low current low dV/dt applications. Grundig used them as coupling caps in audio amplifiers as well and they started to sputter and rumble when they went wrong.
Maarten is offline   Reply With Quote
Reply

Thread Tools



All times are GMT +1. The time now is 4:43 pm.


All information and advice on this forum is subject to the WARNING AND DISCLAIMER located at https://www.vintage-radio.net/rules.html.
Failure to heed this warning may result in death or serious injury to yourself and/or others.


Powered by vBulletin®
Copyright ©2000 - 2024, vBulletin Solutions, Inc.
Copyright ©2002 - 2023, Paul Stenning.