Capacitor values in old schematic. - Page 1
Forum section: electronics / beginners

author: Stuart Coyle
author_rank: Contributor
timestamp: October 22, 2015, 04:50:35 am
content: I have the schematic for my 1980's Roland guitar amplifier here and the capacitors values are written in this manner: 100/16NP or 1/50 etc.Are these simply fractional representations of the value (I expect that NP means non-polar) that is 6.25 and 0.02. uF, nF or pF? Others are just written as 0.01I haven't yet opened the amp up to see what the caps in it actually are.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: October 22, 2015, 05:04:04 am
content: Standard schematic note: components are valued in their natural unit. Resistors in ohms, capacitors in farads, inductors in henries (duh!). Components are further valued by their most common multipliers: polarized capacitors in uF, nonpolarized in pF. Decimals are assumed uF as well. (Probably inductors in uH as well, but if they don't use many in the circuit, they might not bother.)"100/16NP" sounds like 100uF 16V nonpolarized (a particular variety of electrolytic). "0.01" might be applied to a ceramic or film capacitor, also with an assumed voltage rating, perhaps 50V. (And resistors are usually 1/4 or 1/2W by default.)All of this is "unless specified otherwise", of course.You might be able to look around and find a legend or note that describes this. Or it might be in the text. Or, it might be something they took for granted... in which case, you wouldn't know unless you asked.Tim

author: tautech
author_rank: Super Contributor
timestamp: October 22, 2015, 05:15:47 am
content: Quote from: Stuart Coyle on October 22, 2015, 04:50:35 amThe conventions used in old schematics can be quite confusing.Tim has put you on the right track, 100/16NP will be 100uF 16V non polarised, 1/50 will be 1uF 50V etc.All values like 0.02 etc are in uF and likely to be 50 or 100V disc ceramics or some MLCC like Green caps.

author: macboy
author_rank: Super Contributor
timestamp: October 22, 2015, 02:53:06 pm
content: Keep in mind too that in older schematics "microfarad" is often abbreviated as "mf" or "mF". Don't assume it means millifarad.

author: German_EE
author_rank: Super Contributor
timestamp: October 22, 2015, 07:12:35 pm
content: And to make it REALLY confusing a 100pF capacitor is sometimes shown as 100mmF.

author: TimFox
author_rank: Super Contributor
timestamp: October 22, 2015, 08:10:22 pm
content: "mmf" is pronounced "mickey mikes", if I remember correctly. Another common abbreviation is "mfd" for "microfarad".More modern drawings use "uF" for microfarad. I like the convention of placing the letter for the multiplier in place of the decimal point: i.e., 2k2 = 2.2 kohm and 3n3 = 3.3 nF. In that usage, "R" is used for a decimal point when needed, i.e. 4R7 = 4.7 ohms or whatever.The real confusion is "M" meaning "thousand", an accounting convention from the Roman numeral M = 1000. I have a very old Simpson 260 that actually used "M" on the ohmmeter scale to mean thousand, instead of megohms.Many people are far to sloppy about "m" vs. "M" (milli vs. mega). I once saw a relay specified with 10 Mohm contact resistance and 50 mohm insulation resistance, which would be a totally useless part. (I wish I could get majuscule omegas in this text editor.)

author: Stuart Coyle
author_rank: Contributor
timestamp: October 23, 2015, 07:52:35 am
content: Thanks all for the assistance. After looking closer at the schematic and the amp itself it is obvious that the notation is value/voltage as suggested above. Cheers.Now to find the source of that nasty 100Hz hum. (I will be checking out the ground connections and the power supply as a first stop.)

author: tautech
author_rank: Super Contributor
timestamp: October 23, 2015, 08:16:47 am
content: Quote from: Stuart Coyle on October 23, 2015, 07:52:35 amHow do know it's 100 Hz?Have you scoped it?