HP-67 tantalum capacitor: where to buy it?

[sasa]

(10-24-2018 10:16 PM)Archilog Wrote:  HP-97 schematics didn't help so much because capacitance (6,8 uF) is mentionned but voltage is missing.

Higher voltage does not matter at all, it matters minimum projected voltage (usually 30% higher than needed is fine) and capacity. You can think of voltage limit in capacitors as a safety valves - until some maximum projected value they will not blow up and will work properly.

Tantalum caps have quite good characteristic, except they have large tolerance of about 20%, i.e. value 6.8uF +/- 20% is in spec. The main problem with it is that can blow-up as firecracker if reverse polarity or apply higher voltage and catch fire. Nowadays there is quite good LOW and ULTRA LOW ESR electrolytic capacitors with high durability, which also may work correctly.

You can safely use any "tear drop" shaped tantalum capacitor you can found in any electronic shop, which have value of 6.8uF and voltage higher than that, you (i.e in some electronic service) can probably measure on board.

As Tony said, if on plus terminal voltage is +6.25V, safe voltage value for capacitor is 10, 16, 25... Notice that with higher voltage also increase physical size of the capacitor, then be sure there is enough space inside to be placed.