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I'm recapping a vintage amp, and that amp has two larger caps at 2200uF @ 50V. I have sourced some possible replacements, and I'd like some insight into why these are SO different in size, and how I should think about that. (These are both new parts. Original cap not pictured. I know they are slightly different in capacitance--the schematic asked for one thing but the original part was another-- but I think the question here still stands since the specs are so close).

enter image description here

The big one is a Sprague Atom rated to 85°C. (data sheet here). The small one is a JWCO part rated to 105°C. (Data sheet here)-- it's over an inch long, which makes the Sprague huge at like 2.5"+ and way more diameter.

Now, I get that the JWCO is a sort of no-name commodity part that I don't want to use in an audio amplifier-- I get that. But even a Nichicon audio cap at 2200/50 is only going to be a bit over an inch long.

But what I don't get here is WHY these are so enormously different in size, and what's up with the Sprague? Small variances wouldn't surprise me at all based on materials and construction but this is not a small variance. Even the 50-year-old cap I'm replacing is much smaller than the Sprague (though not as small as the JWCO or a Nichicon).

Thanks for any insight. Piecing together my knowledge of components by example!

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    \$\begingroup\$ SE supports HTML entities so you can use ° (degrees symbol) if you want to be cool. (It doesn't work in the comments.) \$\endgroup\$
    – Transistor
    Commented Apr 22, 2020 at 18:30
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    \$\begingroup\$ Different dielectric. Also possibly different ripple current rating. \$\endgroup\$
    – DKNguyen
    Commented Apr 22, 2020 at 18:34
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    \$\begingroup\$ @BenZotto You don't really for the most part anymore than you care how your cellphone works. \$\endgroup\$
    – DKNguyen
    Commented Apr 22, 2020 at 18:42
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    \$\begingroup\$ Ripple current rating and ESR (or tan delta) are probably different. But I'm not seeing them in the Sprague data ... there must be fuller data somewhere. \$\endgroup\$
    – user16324
    Commented Apr 22, 2020 at 18:43
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    \$\begingroup\$ I wouldn’t buy an electrolytic that didn’t have an endurance specified numerically. The Nichicon has 2000 hours specified and that is barely ok. The earlier two don’t have endurance specified hence, you can’t tell how long they will last in moderate temperatures. Buyer beware. See my answer here to understand why. \$\endgroup\$
    – Andy aka
    Commented Apr 22, 2020 at 19:16

3 Answers 3

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Alotta empty air... Those are very old designs (60's), one might use them to restore vintage equipment w/o affecting their appearance.

enter image description here

https://www.lespaulforum.com/forum/showthread.php?177151-Sprague-TVA-Atom-vs-Nichicon-VX-Series

Guitarists and audiophiles spend stupid money chasing "tone", thinking there's some sort of magic in the parts themselves.

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    \$\begingroup\$ Good to know. Thanks. sounds like the Sprague Atoms are a bit physically unique in this respect, so all other equivalent (and equally appropriate) caps will be somewhere near that smaller size and that's nothing to worry about. \$\endgroup\$
    – BZo
    Commented Apr 22, 2020 at 19:11
  • \$\begingroup\$ KyleB - two thoughts, one stranger than the other.. (1) If audiophiles chase the "tone", could it be that added air and the different dimensions of the outer shell cause some differences in parasitic inductance? (2) Electrolytic caps sometimes have explosive end of life, so maybe that larger shell + extra air works as a silencer (slow down waste gases and accidental moving parts) and a partial shield to minimize the collateral damage around it :) \$\endgroup\$
    – quetzalcoatl
    Commented Apr 24, 2020 at 0:10
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    \$\begingroup\$ You don't know any audiophiles, do you ??? ;) LOL You know that standard IEC power cable on the back of your computer? The one that you probably have 12 of in a drawer somewhere? What would you pay for one of those? That cord which is the last little bit of wire between your device and the nearest power transformer on a pole somewhere. How about $85 ?? amazon.com/Audiophile-Power-Amplifier-Carbon-IEC320/dp/… \$\endgroup\$
    – Kyle B
    Commented Apr 24, 2020 at 0:31
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    \$\begingroup\$ Cue monster cables for like 700 bucks a pop... very exploitable industry. Also, "warm lamp sound". \$\endgroup\$
    – htmlcoderexe
    Commented Apr 24, 2020 at 15:09
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Generally speaking, manufacturing has changed significantly since the old Sprague caps were designed, so unsurprisingly there's a lot of blank space in that case. Aluminum electrolytic capacitors can have same specs / be different physically due to a few factors, including lifetime, mechanical robustness, and designed specifically with ESR/ESL in mind. Different electrolytes, layer thickness, encapsulation, electrolyte volume, venting, etc. can all be tweaked to make a component for a specific application. Audio capacitors, You would definitely need more of the electrical specs to know why two "equivalent" caps would be different sizes.

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Be carful, Take a look first to make sure the cap is not in the power rail of the amp. You can't use any old cap due to the fact that if this is a audio amp, the cap is placed across the half bridge if so the type of capacitor is very important. If the cap is blown ,one end I'd blown out are you notice smoke , that means that the cap was used to control what is called pumping you have to make sure the cap has good thermal data, the cap has low ESR, MAKE SURE ITS A POWER CAP WITH WIRE LEADS ARE SCREW TERMINALS.

Because when the amp is on you have two power problem Pumping Very fast current coming from the power stage let say 300khz which will be constant, now you have the audio going thru the amp max freq . Are BW band width That cap will be under hi stress because you have to keep the switch signal near 85dB now the amp has to control pumping the louder the more pumping ,if you listen with no audio make sure you do no heat any time out of the speakers if you do the cap is going to blow, USE A GOLD SEAL CAPACITOR, USE KEMIT ARE CAPACITOR MADE BY MOLLARY CAPACITORS , USE CAPACITORS THAT HAS A RAPID CHARGE AND DISCHARGE LIKE CAPACITORS FOR ( PHOTO FLASH APPLICATION ) THEN YOU ARE SAFE if you wont take a picture of the board where the cap goes and I will find are locate a better part, now you no the cap is at 2200uF so this is in a part of the bulk dc voltage Email me at ( [email protected] ) send picture of the board and the cap and email it to me

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    \$\begingroup\$ This answer might be useful but needs to be written more clearly. Too many typos and explanations aren't clear enough \$\endgroup\$
    – Daniel V
    Commented Apr 24, 2020 at 6:42
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    \$\begingroup\$ Photo flash cap? Screw terminals? 300kHz? It's a "vintage amp", it's not going to have 300kHz on the power supply caps filtering caps. 60Hz maybe \$\endgroup\$
    – Kyle B
    Commented Apr 24, 2020 at 6:48

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