Strange Capacitor Symbol on an old schematic - Page 1
Forum section: electronics / beginners

author: Midphase
author_rank: Regular Contributor
timestamp: January 21, 2025, 07:06:18 pm
content: Can anyone tell me what these are supposed to be? I found some resource that seemed to indicate they are obsolete (i.e. not utilized) components, but there are far too many in the schematic for that to be the case.Are they some weird symbol for polarized electrolytic capacitors? If so which is the + and which is the - side? The line from the left side connects to 15v, so I would assume the left side would be the positive terminal?Many thanks and sorry for the noob question:

author: Fryguy
author_rank: Regular Contributor
timestamp: January 21, 2025, 07:24:15 pm
content: They are electrolytic caps 25V 100µF - i haven't seen this symbol in a long time , can't remember where they came from . . .And yes - the left side is positive !

author: TimFox
author_rank: Super Contributor
timestamp: January 21, 2025, 07:24:36 pm
content: It is a now-unfashionable symbol for a polarized electrolytic capacitor.The small bit is the positive terminal, the larger bit represents the “can”, which is the negative terminal.This follows the physical construction of axial-lead electrolytic capacitors.

author: Midphase
author_rank: Regular Contributor
timestamp: January 21, 2025, 07:32:15 pm
content: Thank you both. This particular schematic is for an old Akai AX 60 Synthesizer from the mid 80's, built in Japan.

author: TimFox
author_rank: Super Contributor
timestamp: January 21, 2025, 07:37:29 pm
content: I seem to remember that symbol in Japanese equipment of that vintage.

author: Analog Kid
author_rank: Super Contributor
timestamp: January 21, 2025, 07:45:49 pm
content: I found this guide to capacitor symbols online:And it doesn't even cover all the different symbols that have been in use. (This picture really covers different capacitortypesrather than different symbols for common types of caps.)

author: Simmed
author_rank: Frequent Contributor
timestamp: January 21, 2025, 07:46:19 pm
content: old style looks good

author: PGPG
author_rank: Frequent Contributor
timestamp: January 21, 2025, 08:20:01 pm
content: Quote from: Midphase on January 21, 2025, 07:06:18 pmThis is the first electrolytic capacitor symbol I've ever seen (I sow it in 1968 reading book written in 1953) and for many years the only one I sow. Others I sow may be around 1985.

author: Konkedout
author_rank: Frequent Contributor
timestamp: January 22, 2025, 03:13:30 am
content: Quote from: PGPG on January 21, 2025, 08:20:01 pmIn USA before my time we used to have capacitor symbols which indicated "outer foil". Those were particularly intended for wound film-foil capacitors, and I think particularly for audio.Intuitively the symbol being asked about seems to show outer foil for one electrode.Curses!! Foiled Again!!https://ennyman.medium.com/curses-foiled-again-ac2fb0f80f97

author: CatalinaWOW
author_rank: Super Contributor
timestamp: January 22, 2025, 04:58:45 am
content: While I agree that the symbol is for an electrolytic capacitor (polarized), I think that its origins are far older and is a direct representation of the first capacitors (Leydon jars).

author: Gyro
author_rank: Super Contributor
timestamp: January 22, 2025, 09:28:08 am
content: I still rather like that symbol. The 'wrap around' is fairly descriptive, if only to remind you that the outer can is at negative potential and a potential accidental contact hazard in negative rail supplies. It could be confused with an outer foil indication if somebody forgot the '+' symbol and value though.The idea that it harks back to the Leyden jar is intriguing, there's probably more than a grain of truth in that. Leyden jars were shown diagrammatically at some point (trying to think back to some of my old books).

author: golden_labels
author_rank: Super Contributor
timestamp: January 22, 2025, 12:01:30 pm
content: Taken from April 1943 issue of “Electronics”,(1)a compilation of most often used symbols. So it seems Konkedout is right.That it couldn’t be just an older symbol for a capacitor is confirmed by it appearing together with other “competing” symbol in the same diagrams. Here’s an example from a 1960 servicing manual:(2)A nice collection of truly old symbols can be found in 1920s “Standard handbook for electric engineers”.(3)They were much more resembling an actual physical structure.(1)Pages 84–86,a copy on Archive.org.(2)Taken froma huge collection of radio servicing manuals, by Beitman. I also bring your attention to component C10 on page 20, together withmulti-section capacitor photos here.(3)Image taken frompage 182.