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I'm repairing some vintage electronics, and there are a handful of cracked ceramic disc capacitors that need replacement. They're mostly for decoupling, but I want to make sure I'm replacing with equivalent or better spec. (I'm also not trying to "upgrade" much to super-modern parts even though I'm sure I could.)

I'm finding the markings inconsistent with what I'm looking at for replacement options, and hoping someone can help me clarify. Here are examples of capacitors I need to replace:

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I get that these are 0.1 μF and 0.47 μF caps, 50 V and 12 V respectively, and that the letter codes of Z5V and Y5U as interpreted via here indicate temperature range and change over range. The 0.47 μF cap has the Z suffix indicating a wide +80/-10% tolerance, I believe, and that is a distinct spec from anything in the three-character code.

Most disc caps I've found as replacements simply don't have the three-letter codes, so I'm not sure how to match them up. I also have found modern ones with and without a capacitance tolerance suffix, e.g. 0.1Z vs 0.1.

Here are some candidate replacements, for example:

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None seem an exact match, but I can't tell if they are appropriate.

My questions are:

  • What is the implied capacitance tolerance if none is noted? (As in the orginal 0.1 μF cap and the third replacement example)
  • What is the implied three-character code if none is noted? (As in the latter two replacement examples)
  • For use as TTL circuit decoupling caps in a piece of computer equipment that will likely get warm but never frigid or fiery, how relevant are the tolerance and temperature ratings?

Thanks for any insight.

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    \$\begingroup\$ ”What is the implied three-character code if none is noted? (As in the latter two replacement examples?)” Probably a bad one, say Y5V. For decoupling, feel free to parallel several ones as long as the voltage rating is sufficient. If you value your time disassembling, solder and reassemble, buy new X7R. \$\endgroup\$
    – winny
    Commented Apr 22, 2023 at 8:09
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    \$\begingroup\$ I wouldn’t obsess too much. TTL is not as needy as high speed CMOS regarding decoupling, so just about anything with a near enough value should perform adequately. The old silicon is more likely to give you grief. Checkout the molded mud resistors and the ic footprints that were done with the Bishop Graphics stickers! 74xx rather than 74LS screams the 70’s. \$\endgroup\$
    – Kartman
    Commented Apr 22, 2023 at 8:22

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Surely when you buy capacitors you need to know their specs. If you care about the specs are they are unknown, don't buy them. So don't buy from weird places that don't know what they are selling. Modern capacitors are so tiny they usually don't have space to print the Z5V or Y5U on them.

And those are very old types and if you want equal or better, you commonly would go for X7R these days.

Even if the current capacitors are rated at 12V and 50V, you can safely substitute them both with 50V or 100V X7Rs. For just TTL chip bypassing purposes, the value is not that exact, and you can likely use 470nF for both.

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