Any reason not to change Tantalum caps for aluminium electrolytics

[Puggie]

I'm re-capping a 70s tape machine (1/4" open reel) and there is a large ammount of tantalum caps in it, is there any reason (cos I can't think of one) why I cannot replace these with Aluminium Electrolytics?

thanks peeps.

[jcx]

probably unnecessary, tant can't "dry out", wet slug tantlum would be obvious if they've leaked

tantalum does have higher distortion so replacing signal coupling tants with nonpolar Al electros should be an improvement - maybe modern mylar film caps physically could fit, any film being better than the best electrolytic

[Puggie]

they are all the Tant bead type, they appear to be polarised on the circuit diagram! We are having a number of cap related problems on the boards so have taken the decision to replace the lot, I was hoping to replace them all with decent quality high temp (it does get a bit warm in there) polarised aluminium electrolytics, would this be an issue, I'm not going for the ultimate in SQ just at least as good as the Tants preferably better.

[jcx]

polar Al electros are fine for power bypass, "polymer electrolyte" types will probably have low enough esl/esr for tant replacement - use higher V and C rating Al where they can fit esp if polymer types are't used - definitely look for low esl

for signal path caps nonpolar Al electros have lower distortion than polar types but fewer options are available in high temp/long life

[anatech]

Hi Puggie,
Are you talking about a Revox or Studer? If so - YES! Do them all. The bad ones are in a whiteish rectangular case with one end rounded.

These days I try to get rid of most the tantalums I see. Normally with new electrolytics.

-Chris

[AndrewT]

Hi,
I seem to remember from the few capacitors tests I have read that tantalums perform better than electrolytics when used for audio. Both in bypassing rubbish to ground and passing signal downstream.

Is my memory going bad or really bad?

[anatech]

Hi Andrew,
Are those the tests from the Seventies and Eighties? I never believed them anyway.

If you look at the articles from Steve Bench, you will see the distortion on tantalums is worse than electrolytics. Besides, bypassing with film caps is better. Newer electrolytics have come a long way since the Seventies.

-Chris

[rdf]

Don't know if it's still the case, the failure mode of older tant caps was to short. If luck's with you when they go just the magic smoke gets out, if not it takes regulated power supplies with it. I believe that's why it's now rare to see them used as PS bypass caps.

[anatech]

Yes, tantalum capacitors tend to short when receiving current pulses. So they are bad for switching power supplies. Remember the Fosgate Punch 250? The tantalum capacitors tended to go up in flames in the power supply.

-Chris

[rdf]

Never had experience with the Fosgate, mine were all with McCurdy radio consoles. A couple of the last series before their eventual exit from field packed a dozen or two 'christmas firecrackers' per channel strip, so named because they only seemed to blow on long weekends. Some consoles had 28 channel strips. The power supplies were also the most byzantine of any console in my experience, not the happiest combination.