Polarity on vintage "Twist Lock" caps? - Page 1
Forum section: electronics / repair

author: Haatveit
author_rank: Regular Contributor
timestamp: June 22, 2018, 07:51:56 pm
content: As the title says. I have no idea how to decipher these arcane markings, squares, triangles, what? Anyone?I'massumingthat the pins connected to the outer case is negative, but I don't want to make assumptions... It's a bit hard to see the traces on the PCB so I can't tell from looking (big fat transformer covering most of it).

author: glarsson
author_rank: Frequent Contributor
timestamp: June 22, 2018, 07:58:49 pm
content: 200 uF between casing and pin marked with a square.The same case could also be used for components containing two or three capacitors. The other pins would then use some other symbols like triangle and circle.

author: Haatveit
author_rank: Regular Contributor
timestamp: June 22, 2018, 08:24:05 pm
content: Quote from: glarsson on June 22, 2018, 07:58:49 pmThanks! So the out casing would be a commonNegativeassuming these caps are polarized, and the inner pins would be the respective positive for different embedded caps?

author: andy2000
author_rank: Frequent Contributor
timestamp: June 22, 2018, 08:28:16 pm
content: Quote from: Haatveit on June 22, 2018, 08:24:05 pmThe can is almost always negative, and it would be labeled if that wasn't the case.

author: Cyberdragon
author_rank: Super Contributor
timestamp: June 23, 2018, 12:53:00 am
content: The can is sometimes not connected. In that case there will be an isolated common on the bottom.

author: Chris56000
author_rank: Frequent Contributor
timestamp: June 23, 2018, 11:58:33 am
content: Hi!From reading immumerable Heathkit and other American circuit–diagrams I can confirm the square, triangle, half–moon, triangle, etc., etc., always indicates POSITIVE capacitor terminals with can common negative – I think "Sam's Photofacts" key each symbol to the relevant capacitor on the circuit diagram!Usually the square is the one used for the reservoir (rectifier output) rated section, whilst the others are for lower ripple–current rated sections for decoupled h.t./l.t. lines!British multi–section electrolytic capacitors nearly always colour–code the tags, these can be looked up in older Radio and TV reference books, but RED is nearly always the reservoir, YELLOW first smoothing, GREEN second smoothing and so on!Both British & American twist–lock capacitors often have a hole punched in one of the twist–tabs to allow wiring, etc., to be connected to the can (negative) terminals!Chris Williams

author: Bashstreet
author_rank: Frequent Contributor
timestamp: June 23, 2018, 05:44:24 pm
content: Quote from: andy2000 on June 22, 2018, 08:28:16 pmYes this is also my understanding . Can one actually test capacitor polarity with multi meter ?

author: Chris56000
author_rank: Frequent Contributor
timestamp: June 23, 2018, 06:39:48 pm
content: Hi!QuoteNo, the meter test voltage from modern DMMs is usually too low - you need a current-limited variable power supply for this!My experience with multi-section capacitors is that the chances of finding anything other than can negative is virtually nil!However, if you come across very old multi-section capacitors with wire leads, (tend to be mainly American) and the lettering has gone or isn't clear, a variable PSU set to about 10mA current-limit will usually identify the polarity for you - connect the PSU to the capactior leads any way round - if the current rapidly limits without much rise in voltage, then you've got it wrong way round!Chris Williams

author: Bashstreet
author_rank: Frequent Contributor
timestamp: June 23, 2018, 07:43:32 pm
content: Quote from: Chris56000 on June 23, 2018, 06:39:48 pmMaybe someone will figure out how to make simple tester that will check polarity.It could be very handy in some situations.Cheers.

author: Decapitator
author_rank: Contributor
timestamp: June 30, 2018, 08:59:35 am
content: Type FP (twist tab) capacitors were made in negative can and floating can varieties. A negative can type could be mounted on a phenolic insulating plate and covered with a phenolic insulating can if a positive ground was required. The symbols blank, square, triangle, circle would identify each section individually in a multi section can. Each section could have a different capacitance and working voltage ratings.The number 235-7804 on your example is a manufacturer (235= PR Mallory) and date code (4th week of 1978) which could be useful in dating a piece of vintage equipment. Similar date codes can often be found on pots.http://www.technicalaudio.com/pdf/Electronics_Catalog_Extracts/Mallory_FP-WP_Series_capacitors_1985.pdf