( 
)Ever wonder what those numbers are on vintage capacitors? This article will cover most aspects of vintage Paper in Oil capacitors codes so they can be easily identified. These typse of capacitors are quite popular among the audio diy enthusiest for it's unique sound quality and reliability. Love them or hate them the old paper in oil capacitors were built to last. Rarely do you find any that exibit current leakage these caps are components to be reckoned with. Todays oil capacitors run the average audio dork like me $30+ each. Hence the popularity of these vintage caps is steadily growing when when the average Audio dork can pick up a pair for under $10 on eBay. Unfortunately as the popularity grows the global supply of these caps that have been out of production since the early 80's gets depleted. Anyways, leta move on my point. First of all I don't feel like writing an article for the rest of the night so I'm just gonna cover the most commonly found and used types. Information on these types of capacitors is almost impossible to find on the web so this information is from my own personal research and experiments such as deconstructing every type I have seen. If anyone spots any errors please correct me.
Lets start with the best way to identifying a paper in oil capacitor. That would be from the CP or CPO code. Usually fallowed a number, a letter and then another number ex. CPO5A1. All of which describe the dielectric, construction and type of paper in oil. CP or CPO can be remembered as Capacitor Paper or Capacitor Paper Oil. You can be assured that a cpacitor is a paper in oil type if it has a CPO### code on it. So here are a few codes and definitions...
CPO4 and CPO5 - These types have an inserted tab construction making them the smaller, compact in size paper in oils. These types are hermetically sealed glass to metal terminals. CPO4 types have a plain metal casing where CPO5 types have an insulating sleeve. The insulating sleeve can be a clear tape, plastic or colored rubber. These types meet or exceed MIL-C-25C requirements -55° C to +125° C and can have a tolerance form 10% to 20%. CPO5 types are a little more desirable as it minimizes the chance of a short. If not careful one can cause some problems if somehow something comes in contact with the CPO4 casing completing a connection with something else.
CPO8 and CPO9 - These types have an extended foil or non inductive section construction. Also hermatically sealed glass to metal terminals. CPO8 has a plain metal casing where CPO9 has an insulated sleeve. These types meet or exceed MIL-C-25C requirements -55° C to +125° C and can have a tolerance from 10% to 20%.
Floating Case and Case Gounded:
The 5th character in the CPO codes indicates wether or not it is case grounded or insulated / floating. This is represented by an A or B. Type A means that the terminal leads are insulated or floating from the metal casing. Type B means case grounded. In type B's this is easy to see because one of the terminal leads are soldered directly to the outside of the casing. Only one end of the capacitor will have a glass end seal. Examples would be CPO4B1 which would indicate it's an inserted tab constructed capacitor, case grounded. This type of construction makes ths cap much smaller size. For example a .1uf / 100v cap will be roughly the same size as a .1uf / 600v cap. One must be extra careful when dealing with B type capacitors! With what might be some much needed relistate in your gear could come at a price if you do not give full attention to detail. Very easily you can you ruin sensitive components or even elctricute yourself. I would suggest putting some type of sleeving on CPOP4 and CPO8, A and B type capacitors. maybe some tape or shrink wrap tubing.
Probably the most popular paper in oil of all are Sprague's Vitamin Q capacitors. Sprague along with all of those other infamous capacitor mfg's like Astron, Gudeman, West-Cap, C-D, Good-All, Micamold among others used there own series identification codes along with the standard CPO codes. I will not get into all of them cause like i said i dont want to be typing all night. But i will throw out a few tips for identifying some of them starting with everyone favorite the Vitamin Q.
Sprague Vitamin Q capacitors had many different series / types
Vitamin Q types exceed performance requirements of MIL-C25A
Type 91P - These types have an inserted tab construction making them the smaller. Hermetic sealed glass to metal and an 85° C operating temp.
Type 96P - Equivelent to CPO4 & CPO5 types. Also inserted tab construction, hermetic sealed but with a 125° C operating temp.
Type 191P - These have an extended foil construction, hermetic sealed with a 85° C operating temp.
Type 196P - Equivelent to CPO8 & CPO9 types. Also extended foil construction, hermetic sealed but with a 125° C operating temp.
Vitamin Q capacitors usually have an 11 digit code. The first 3-4 digits indicating series construction. The fallowing 3 digits indicate capacitance. Fallowed by a digit indicating tolerance, which is represented by a 9 = 10% or a 0 = 20%. The fallowing digit or 8th character idicates voltage x 100. And fallowed by 2 characters indicating terminal and vibration grade which i wont get into.
ex. 191P47293S4 = Vitamin Q .0047uf / 300v 10%...
Ok i covered the most popular and abundunt types for the most part. To end this article im gonna name off a few codes or tips to look for on these vintage caps so you can confrim that are indeed paper in oil capacitors and not just some polyester film cap in a metal casing. hope this helps some people out or is at least is some what good knowledge to have. Like i said i didn't cover everything so if you have questions feel free to contact me through my eBay store AudioGrade
Vitamin Q's - SR196P, 181P, 86P, P68, CR, CPV
Cornell-Dubilier - TWU, TWS
Astron - TQF, TQS
Pyramid - EPGIXV
Good-All, Micamold, Gen. Instr. - 354A, 627G, 613G
West-Cap - 815, FSN
Other Standard Paper in Oil codes that represent type of casing such as rectangular metal cans, bathtub, threaded end with nut, chassis mountable and o-tab. These are just the initial digits and will be fallowed by other digits indicating specs. -
CP53, CP61 to CP72, CP10, CP11, CP12, CP28, CR, BP
A good rule of thumb for these types is to remember that an A or B after the initial 2 to 4 digits indicates case floating or case grounded. Like talked about above. ex. CP11B3 = Paper in Oil with threaded end and nut, case grounded. CP11A would be a floating case .
Omar Masri from AudioGrade
Lets start with the best way to identifying a paper in oil capacitor. That would be from the CP or CPO code. Usually fallowed a number, a letter and then another number ex. CPO5A1. All of which describe the dielectric, construction and type of paper in oil. CP or CPO can be remembered as Capacitor Paper or Capacitor Paper Oil. You can be assured that a cpacitor is a paper in oil type if it has a CPO### code on it. So here are a few codes and definitions...
CPO4 and CPO5 - These types have an inserted tab construction making them the smaller, compact in size paper in oils. These types are hermetically sealed glass to metal terminals. CPO4 types have a plain metal casing where CPO5 types have an insulating sleeve. The insulating sleeve can be a clear tape, plastic or colored rubber. These types meet or exceed MIL-C-25C requirements -55° C to +125° C and can have a tolerance form 10% to 20%. CPO5 types are a little more desirable as it minimizes the chance of a short. If not careful one can cause some problems if somehow something comes in contact with the CPO4 casing completing a connection with something else.
CPO8 and CPO9 - These types have an extended foil or non inductive section construction. Also hermatically sealed glass to metal terminals. CPO8 has a plain metal casing where CPO9 has an insulated sleeve. These types meet or exceed MIL-C-25C requirements -55° C to +125° C and can have a tolerance from 10% to 20%.
Floating Case and Case Gounded:
The 5th character in the CPO codes indicates wether or not it is case grounded or insulated / floating. This is represented by an A or B. Type A means that the terminal leads are insulated or floating from the metal casing. Type B means case grounded. In type B's this is easy to see because one of the terminal leads are soldered directly to the outside of the casing. Only one end of the capacitor will have a glass end seal. Examples would be CPO4B1 which would indicate it's an inserted tab constructed capacitor, case grounded. This type of construction makes ths cap much smaller size. For example a .1uf / 100v cap will be roughly the same size as a .1uf / 600v cap. One must be extra careful when dealing with B type capacitors! With what might be some much needed relistate in your gear could come at a price if you do not give full attention to detail. Very easily you can you ruin sensitive components or even elctricute yourself. I would suggest putting some type of sleeving on CPOP4 and CPO8, A and B type capacitors. maybe some tape or shrink wrap tubing.
Probably the most popular paper in oil of all are Sprague's Vitamin Q capacitors. Sprague along with all of those other infamous capacitor mfg's like Astron, Gudeman, West-Cap, C-D, Good-All, Micamold among others used there own series identification codes along with the standard CPO codes. I will not get into all of them cause like i said i dont want to be typing all night. But i will throw out a few tips for identifying some of them starting with everyone favorite the Vitamin Q.
Sprague Vitamin Q capacitors had many different series / types
Vitamin Q types exceed performance requirements of MIL-C25A
Type 91P - These types have an inserted tab construction making them the smaller. Hermetic sealed glass to metal and an 85° C operating temp.
Type 96P - Equivelent to CPO4 & CPO5 types. Also inserted tab construction, hermetic sealed but with a 125° C operating temp.
Type 191P - These have an extended foil construction, hermetic sealed with a 85° C operating temp.
Type 196P - Equivelent to CPO8 & CPO9 types. Also extended foil construction, hermetic sealed but with a 125° C operating temp.
Vitamin Q capacitors usually have an 11 digit code. The first 3-4 digits indicating series construction. The fallowing 3 digits indicate capacitance. Fallowed by a digit indicating tolerance, which is represented by a 9 = 10% or a 0 = 20%. The fallowing digit or 8th character idicates voltage x 100. And fallowed by 2 characters indicating terminal and vibration grade which i wont get into.
ex. 191P47293S4 = Vitamin Q .0047uf / 300v 10%...
Ok i covered the most popular and abundunt types for the most part. To end this article im gonna name off a few codes or tips to look for on these vintage caps so you can confrim that are indeed paper in oil capacitors and not just some polyester film cap in a metal casing. hope this helps some people out or is at least is some what good knowledge to have. Like i said i didn't cover everything so if you have questions feel free to contact me through my eBay store AudioGrade
Vitamin Q's - SR196P, 181P, 86P, P68, CR, CPV
Cornell-Dubilier - TWU, TWS
Astron - TQF, TQS
Pyramid - EPGIXV
Good-All, Micamold, Gen. Instr. - 354A, 627G, 613G
West-Cap - 815, FSN
Other Standard Paper in Oil codes that represent type of casing such as rectangular metal cans, bathtub, threaded end with nut, chassis mountable and o-tab. These are just the initial digits and will be fallowed by other digits indicating specs. -
CP53, CP61 to CP72, CP10, CP11, CP12, CP28, CR, BP
A good rule of thumb for these types is to remember that an A or B after the initial 2 to 4 digits indicates case floating or case grounded. Like talked about above. ex. CP11B3 = Paper in Oil with threaded end and nut, case grounded. CP11A would be a floating case .
Omar Masri from AudioGrade
Guide created: 11/14/08 (updated 09/21/09)
Thank you for voting. If your vote meets our 
