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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.

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Old 25th Jul 2019, 2:37 pm   #21
Maarten
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Default Re: How to test low voltage capacitors?

Quote:
Originally Posted by Craig Sawyers View Post
Quote:
Originally Posted by Uncle Bulgaria View Post
Do I buy higher-voltage-rated modern tantalums (the big suppliers seem to offer them at several pounds a go, which makes this option alarming), or are film or aluminium types worth going for (if they fit)? The particular 1979 circuit diagram for this unit that prompted the question specifies six different capacitor types with different symbols, so whether this is still valid today is a question I am not qualified to answer.
In the last post I mentioned Tektronix. In one of the longest continuously manufactured products (the 7A26 dual amplifier plug in) they started with tant beads for many years. Then after repeated failures, in later plug ins they substituted aluminium electrolytics.

Craig
Same with Revox. I don't have the bulletin but I have from someone who restores them that Revox after a few years sent out a bulletin regarding replacement of all tantalums.
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Old 28th Jul 2019, 12:58 pm   #22
Uncle Bulgaria
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Default Re: How to test low voltage capacitors?

Craig - surely changing the capacitance would affect the functioning of the circuit? I can't say I'm knowledgeable to do more than just slavishly copy what's in the circuit diagram when doing repairs, but it's an interesting proposal.

As far as this tantalum proposition goes, I've replaced all on the playback amplifier and the difference is night and day on the headphones. I won't use any of those 'audiophile' terms, but where the sound was before 'fine', it's now 'very good'. No muffledness or the hisses and crackles that there were before.

Considering the tantalum C316 was the cause of the channel failing, I'm happy to believe the others were not too happy after forty years, even without the ability to definitively test them.

I'm a bit sad I haven't any wet slugs though. Better search in the garden...
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