Vintage Tubular Capacitors: Paper or Polymer?

by Jesse Acorn

Non-polarized capacitors (aka condensers) with more-or-less cylindrical bodies have been used for the entire history of commercial electronics, and many varieties are still produced. They are simple components, each consisting of two metal electrodes rolled into a cylinder with a dielectric material between them. With very few exceptions, this dielectric is either paper, plastic film, or both wound together as in hybrid capacitors (often called Difilm, which was Sprague's trademark). This capacitor roll is then encased in a tubular package, typically made of either hard plastic, ceramic, cardboard sealed with wax, or metal sealed with rubber or glass.

When restoring or rebuilding vintage electronics, especially vacuum-tube equipment of the 1960s and earlier, "re-capping" is often done. This is the act of replacing every electrolytic and paper capacitor in something, for the sake of improving reliability, and sometimes as part of necessary repairs. As for electrolytics, suffice it to say that their main problems are evaporation of the liquid electrolyte and "deforming" of the oxide dielectric; these defects basically result in failing open or shorted repectively, with the former being most common. In some applications, an electrolytic failing short can damage expensive and/or difficult-to-replace parts, such as power transformers and rectifier tubes. Luckily, electrolytic capacitors are easy to identify because of their distinctive packages, large size, high capacitance, and polarity.

Paper capacitors are also among the most troublesome parts. The paper tends to decompose and absorb moisture, causing increased electrical leakage; eventually, the capacitor may fail short. Depending on application, this failure mode can destroy transformers and tubes, or in rare cases create a shock or fire hazard. Now, keep in mind that reliability depends somewhat on the type of paper, its impregnation (wax, oil, polymer, etc.), and the tightness of the package's seal (with hermetically-sealed parts faring best). The worst types tend to be wax-paper capacitors with wax-coated cardboard bodies, since those are the least well-sealed, and the wax is not very stable, besides that such caps are mostly over 60 years old. Some plastic-bodied types are also notoriously bad, such as "Bumblebees" with oil-filling spouts. Without knowing the reputation of a particular type, recapping should be considered after measuring one or more suspect parts and considering factors such as package design (e.g. hermetic or non-hermetic), type of impregnation, etc.

Conversely, there is no reason to replace plastic film capacitors preventatively, because all polymer dielectrics age extremely well in comparison to paper—only in the rare event of failure should they be replaced. I also tend to leave Hybrid capacitors in place, since if the paper degrades, the permissible working voltage may decrease (and capacitance may drift slightly), but at least the polymer prevents leakage from developing prior to a breach of the dielectric, which I've never seen happen so far. In fact, my main purpose here is to prevent wasted effort replacing plastic caps, not to encourage replacing paper caps, which can sometimes be left in place without worry.

So, replace some paper caps, leave plastic caps. No problem, right? Well, there is a problem: they often look identical. There is no way to reliably distinguish between them without either breaking them open, or already knowing what's inside the given type. There is a lot of misinformation about this topic online. I have read in multiple places that "Bumblebees" without spouts are mylar or hybrid. They aren't. Every one that I've dissected was just paper. I've even read that most molded-plastic capacitors in vintage tube electronics are plastic film, and that the polymer breaks down just like paper. This is also completely false; most of them are paper, with the transition to plastic film being made primarily in the early '60s, and those that are polymer do not develop leakage the way paper does. In fact, even the earliest polymer types usually test as good as new, with virtually no leakage, and capacitance well within tolerance.

Tired of misinformation, and more often a plain lack of information, I decided to make a list of vintage tubular capacitors and their dielectrics. It contains only info that I have personally verified or taken from official documents. By "personally verified", I mean that I have broken open at least one capacitor and looked inside. Also note that I have only included the most potentially misleading cardboard-bodied types, since these are nearly all paper. Many were made before the commercial application of polyester—the first common polymer dielectric—dafter all. The list would be a real mess if every cardboard type I'd ever seen were included!

Also included are many Soviet-made tubular caps, which are common on eBay and similar sites. Notoriously unreliable paper types (such as БМ-2, БМТ-2, and МБМ) were produced in great quantities well into the 1980s, long after such capacitors were abandoned by the West. They often appear in Soviet-made tube and solid-state electronics.

"Good" dielectrics are bolded, and one very rare and practically unknown dielectric is italicized. So, without further ado, here is the list:

Brand:Type:Text Color:Body Material & Style:Dielectric:Notes:
? "MOLDED" Black Molded plastic, blue w/ white label PlasticPossibly made by Mallory, sometimes called Ajax
Aerovox "Hi-Q" Black Ceramic, white Ceramic
Aerovox B161Y White Molded plastic, black HybridPlastic film and Kraft paper.
Aerovox BE "Bi-electric" White Molded plastic, black HybridRadial leads. Polyester and paper.
Aerovox K323Z Black Metal PlasticMetallized polycarbonate, hermetic.
Aerovox P82Z White Cardboard, black PaperMetallized paper, Hyvol K (PCB oil) impregnated.
Aerovox P83Z White Molded plastic, black PaperMetallized paper, Hyvol K (PCB oil) impregnated.
Aerovox P84CM "Duramic" Black Ceramic, white Paper
Aerovox P85N Black Cardboard (?) Paper
Aerovox P88 "Duranite" White Molded plastic, blue Paper
Aerovox P89M Black Metal PaperOil-filled. Suffixes A, AP, AY, P, X, XP, XY, and Y.
Aerovox P89Z Black Metal PaperMet. paper, Hyvol K or M imprg., hermetic. Suffixes XP, XY, Y.
Aerovox P92ZN Black Molded plastic, whitePaperMetallized paper, Aerolene / Hyvol N (PCB oil) impregnated.
Aerovox P123S Black Metal PaperHyvol S impregnated, hermetic. Various suffixes.
Aerovox P123Z Black Metal PaperMet. paper, Hyvol S imprg., hermetic. Various suffixes.
Aerovox P123ZN Black Metal PaperMet. paper, Hyvol N imprg., hermetic. Various suffixes.
Aerovox P123ZNNBlack Metal PaperMet. paper, type NN solid impregnant, hermetic. Various suffixes.
Aerovox P151N "Autopass" White Molded plastic, black PaperRadial leads.
Aerovox P159N "Polycap" White Molded plastic, black PaperRadial leads.
Aerovox P161N "Polycap" White Molded plastic, black Paper
Aerovox P323S Black Metal PaperHyvol S impregnated, hermetic. Various suffixes.
Aerovox P8292ZN Silver Molded plastic, black PaperMetallized paper.
Aerovox V84C "Aerofilm" Black Ceramic, white PlasticPolyester.
Aerovox V146XR "Aerofilm" Black Wrapped plastic, yellowPlasticPolyester.
Aerovox V161 "Aerofilm" White Molded plastic, black PlasticPolyester.
Aerovox VBC "Vibrator Buffer" Red Ceramic, white PaperHyvol M (PCB oil) impregnated.
Ajax PMTC Black Ceramic, white Paper
Armaco JCP-TNN-R Blue Ceramic, white Paper
Astron AP Green Ceramic, white PaperNo type label.
Astron AQ "Meteor" Black Metal PaperF suffix = floating, P suffix = plastic sleeve.
Astron ARMF Black Metal PaperMineral oil filled.
Astron ARMG Black Metal PaperMineral oil filled.
Astron BP "Blue Point"Green Molded plastic, yellow w/ blue fill PaperNo type label. Mineral oil impregnant. Note changeover!
Astron BP "Blue Point"Green Molded plastic, yellow w/ blue fill HybridNo type label. Solid thermoset impregnant. Note changeover!
Astron ML "Metalite" Black Cardboard, painted silver, wax-coated PaperHydrocarbon wax impregnated.
Astron MLL "Hy-Met" Black Cardboard, wax-coated Paper
Astron MQC "Metalite" Black Metal PaperMet. paper, mineral wax. F suffix = floating, P suffix = plast. sleeve.
Astron MQZ "Metalite" Black Metal PaperMetallized paper. F suffix = floating, P suffix = plastic sleeve.
Astron MQL "Hy-Met" Black Metal PaperMet. paper, hermetic. F suffix = floating, P suffix = plastic sleeve.
Astron MRF "Metalite" Black Metal PaperMineral wax impregnated, hermetic. P suffix = plastic sleeve.
Astron MRG "Metalite" Black Metal PaperHermetic. P suffix = plastic sleeve.
Astron RQL Black Metal PlasticMetallized polyester, hermetic.
Astron TQ "Meteor" Black Metal PaperF suffix = floating, P suffix = plastic sleeve.
CCL OS Black Ceramic, white Paper
Condenser ProductsASG "Glassmike" Black Glass w/ metal ends, red PlasticPlastic film, silicone-filled, hermetic.
Condenser ProductsLSG "Glassmike" Black Glass w/ metal ends, blue PlasticPlastic film, silicone-filled, hermetic.
Condenser ProductsTACM "Plasticon" Black Metal PlasticTeflon.
Condenser ProductsTAG "Plasticon" Black Glass w/ metal ends PlasticTeflon.
Cornell DubilierBC "Plug-In" White Molded plastic, black PaperRadial leads.
Cornell DubilierCUB Yellow Molded plastic, black Paper
Cornell DubilierDT "Dwarf Tiger" Blue Cardboard, wax-coated PaperHalowax impregnated.
Cornell DubilierDPMS White Dipped plastic, brown HybridRadial leads. Fixfil impregnated. No type marking on parts.
Cornell DubilierMD "Blue Tiger" Blue Cardboard, wax-coated PaperDykanol D (PCB oil) impregnated.
Cornell DubilierMP "Pup" White Cardboard, blue or black, wax-coated PaperMetallized paper, wax impregnated.
Cornell DubilierMPX White Cardboard, wax-coated PaperMetallized paper, Polykane impregnated.
Cornell DubilierMPY "Super Pup" Yellow or white Cardboard, painted black PaperMetallized paper, polyester resin impregnated.
Cornell DubilierMTM "Metapup" Black Metal PaperMetallized paper, non-hermetic.
Cornell DubilierMTV Black Metal w/ cardboard sleevePaperOil soaked paper, hermetic.
Cornell DubilierMTW "Sealpup" Black Metal PaperMetalized paper, hermetic.
Cornell DubilierMTX Black Metal PaperMetalized paper, Polykane impregnated, hermetic.
Cornell DubilierPJ "Tiny Chief"Yellow Molded plastic, pink Paper
Cornell DubilierPKM "Black Cat"White Molded plastic, black HybridPaper and polyester, Fixfil impregnated.
Cornell DubilierPM Black Molded plastic, green PlasticPolyester.
Cornell DubilierPTE "Blue Cub" White Molded plastic, blue PaperVikane impregnated.
Cornell DubilierSTM "Miniroc" Black Ceramic, white PlasticPolyester.
Cornell DubilierTMC Black Metal Paper
Cornell DubilierTVC Black Metal PaperDykanol B (PCB oil) soaked paper.
Cornell DubilierTWH "Demicon" Black Metal PaperWax paper, hermetic.
Cornell DubilierTWC "Demicon" Black Metal PaperDykanol C (PCB oil) soaked paper, hermetic.
Cornell DubilierTWU "Demicon" Black Metal PaperDykanol U (PCB oil) soaked paper, hermetic.
Cornell DubilierTWMA "Demicon" Black Metal PlasticPolyester, hermetic.
Cornell DubilierType I Molded Molded plastic, black PaperSquare domino with silver 1st dot.
Cornell DubilierWMF Black Wrapped plastic, yellow PlasticPolyester and foil.
Elmenco MPD Silver Dipped plastic, brown HybridRadial leads. No type markings on parts, just "EM".
ERO Black Metal w/ beige epoxy ends Paper
Erofol I „K“ Black Clear plastic, green Plastic
Eroid „K“ F Black Clear plastic, orange Paper
Facon 020 White Clear glass w/ black paper label Paper
Film Capacitors IncA1 Black Ceramic w/ metal ends PlasticPolystyrene, hermetic.
Film Capacitors IncA4 Black Metal PlasticPolystyrene, hermetic.
Film Capacitors IncC1 Black Ceramic w/ metal ends PlasticTeflon, hermetic.
Film Capacitors IncD6 Black Ceramic w/ metal ends PlasticHermetic.
Film Capacitors IncHD4 Black Metal PlasticPolyester, hermetic.
Good-All 522M Black Cardboard, wax-coated PaperStrong smell upon opening, no measurable leakage.
Good-All 600UE White Molded plastic, brown Plastic
Good-All M503 Black Cardboard, wax-coated PaperStrong smell upon opening, no measurable leakage.
Hammond AO-500 Black Ceramic, white PlasticRebranded.
Hammond AO-00747 Black Metal w/ green or yellow plastic sleevePaperRebranded, sometimes John Fast.
Hammond AO-18727 Black Cardboard, wax-coated PaperRebranded, sometimes Micamold or EUC.
Hunts A White Molded plastic, brown PaperVery brittle plastic body, often cracked.
Hunts AC White Molded plastic, black Paper
John Fast F369 White Molded plastic, black Plastic
Mallory GEM Black Molded plastic, brown, squared-off Paper
Mallory GEM Black Molded plastic, brown, squared-off HybridSelect values.
Mallory GEM White Molded plastic, brown, rounded PlasticChangeover somewhere between 1960–65.
Mallory MT Black Metal w/ cardboard or plastic sleeve PaperHermetic.
Mallory OT Black Metal w/ cardboard or plastic sleeve PaperHermetic.
Mallory PlascapRed or greenMolded plastic, yellow Paper
Mallory PVC White Dipped plastic, dark brown PaperRadial leads. Note changeover!
Mallory PVC Black Dipped plastic, orange PlasticRadial leads. Note changeover!
Micamold Tropicap Yellow Molded plastic, green Paper
Micamold Type 345 Molded and black Molded plastic, brown PaperRectangular domino.
Neokon „85“ Black Molded plastic, yellow Paper
Planet Rockette Black Molded plastic PaperPlastic impregnated.
Pyramid IMP Yellow Molded plastic, black Paper
Rubycon CP-A Black Metal w/ gray plastic shrinkwrapPaper
Sangamo Black Molded plastic, pink Paper
Sangamo 30 Black Molded plastic, green Paper
Sangamo 33 Black Molded plastic, green Paper
Sangamo 33M Black Molded plastic, green Plastic
Sangamo Canada Molded & BlackMolded plastic, pink Paper
Sangamo Canada 30 Molded & BlackMolded plastic, beige or pinkPaper
Sprague "Bumblebee" (with spout)Molded plastic, black Paper
Sprague "Bumblebee" (no spout)Molded plastic, black Paper
Sprague 73P Yellow Molded plastic, black PaperWith filling spout on one end.
Sprague 91P "Vitamin Q" Black MetalPaperVitamin Q polymer impregnated, hermetic.
Sprague 96P "Vitamin Q" Black MetalPaperVitamin Q polymer impregnated, hermetic.
Sprague 102P "Thru-Pass" Black MetalPaperVitamin Q polymer impregnated, hermetic.
Sprague 103P "Thru-Pass" Black MetalPaperVitamin Q polymer impregnated, hermetic.
Sprague 114P "Styracon" Black MetalPlasticPolystyrene, hermetic.
Sprague 118P "Difilm" Black MetalHybridMet. paper & polyester film, mineral wax imprg., hermetic.
Sprague 118P-S2 Black Metal PaperMetallized paper, hermetic.
Sprague 121P Black Metal Paper Metallized paper, hermetic.
Sprague 127P "Filmite E" Black Metal PlasticPolyester.
Sprague 139P "Filmite F" Black Metal Plastic
Sprague 141P "Filmite G" Black Metal PlasticTeflon.
Sprague 142P "Filmite G" Black Metal PlasticTeflon.
Sprague 155P "Black Beauty"Red Molded plastic, black PaperMetallized paper.
Sprague 156P "Black Beauty"Red Molded plastic, black PaperMetallized paper.
Sprague 160P "Black Beauty"Red Molded plastic, black Hybrid
Sprague 185P "Telecap Difilm" Yellow Molded plastic, black Hybrid
Sprague 191P "Vitamin Q" Black Metal PaperVitamin Q polymer impregnated, hermetic.
Sprague 192P "Pacer" Black Dipped plastic, orange PlasticPolyester and foil.
Sprague 196P "Vitamin Q" Black Metal PaperVitamin Q polymer impregnated, hermetic.
Sprague 205P Black Glass w/ metal endsHybridPaper and polyester, impregnated with Vitamin Q polymer.
Sprague 220P "Orange Drop" Black Dipped plastic, orange HybridRadial leads.
Sprague 225P "Orange Drop" Black Dipped plastic, orange PlasticRadial leads. Polyester and foil.
Sprague 259P "Metfilm K" Black Metal PlasticMetallized polycarbonate, hermetic.
Sprague 260P "Metfilm K" Black Metal PlasticMetallized polycarbonate, hermetic.
Sprague 416P "Yellow Jacket" Black Wrapped plastic, yellow Plastic
Sprague 418P "Orange Drop" Black Dipped plastic, orange PlasticPolyester and foil. Radial leads.
Sprague BF "Isofarad" Red (or black)Molded plastic, black (occ. painted red)PlasticPrefix 5.
Sprague DF "Orange Drop" Black Dipped plastic, orange PlasticMetallized film. Radial leads. Prefixes 1 and 2.
Sprague MB "Buffer" Black Cardboard, wax-coated Paper
Sprague MB "Buffer" Yellow Molded plastic, black PaperWith filling spout on one end.
Sprague MB "Buffer" Red Molded plastic, black HybridNo spout. Note changeover; may not all be hybrid?
Sprague PS "Orange Drop" BlackDipped plastic, orange HybridPaper and polyester, HCX imprg. Prefixes 2, 4, 6, 10, 16, & 20.
Sprague PX BlackMetal w/ cardboard sleevePaperOil-filled, oil-impregnated, hermetic.
Sprague SE "Autocon" Yellow Molded plastic, black PaperRadial leads. HCX plastic impregnated. Prefixes 2, 4, and 6.
Sprague TM "Black Beauty" Yellow Molded plastic, black PaperWith filling spout. Prefixes 2, 4, 6, & 10.
Sprague TM "Difilm Black Beauty" Red Molded plastic, black HybridNo spout. Paper and polyester. HCX imprg. Prefixes 2, 4, 6, & 10.
Sprague TVM "Black Beauty" Yellow Molded plastic, black PaperMineral oil impregnated.
Sprague WF "Yellow Jacket" Black Wrapped plastic, yellowPlasticPolyester and foil. Prefix 2.
Sprague CP04 Black Metal PaperVitamin Q polymer impregnated, hermetic.
Sprague CP05 Black Metal w/ clear plastic sleevePaperVitamin Q polymer impregnated, hermetic.
Sprague CP08 Black Metal PaperVitamin Q polymer impregnated, hermetic.
Sprague CP09 Black Metal w/ clear plastic sleevePaperVitamin Q polymer impregnated, hermetic.
Sprague CP26 Black Metal w/ clear plastic sleevePaperMineral oil impregnated, hermetic.
Sprague CP28 Black Metal w/ clear plastic sleeve & bracketPaperMineral oil impregnated, hermetic.
Standard Black Cardboard, uncoatedPlastic
Sun Capacitors Black Ceramic, white PaperTranslucent brown end filler.
Suzuki OIL JCP-A Black Metal w/ gray plastic shrinkwrap Paper
TCC 493 "Plastiseal" Black Cardboard, soft-plastic-coated Paper
TCC 693 "Plastiseal" Black Cardboard, soft-plastic-coated Paper
USSR БМ-2 / BM-2 Black Metal PaperNon-hermetic. Often leaky.
USSR БМТ-2 / BMT-2 Black Metal PaperNon-hermetic. Often leaky.
USSR К40П-1 / K40P-1 Molded Molded plastic Paper
USSR К40П-2А / K40P-2A Black Metal, painted PaperNon-hermetic.
USSR К40П-2Б / K40P-2B Black Metal, painted PaperNon-hermetic.
USSR К40У-9 / K40U-9 Black Metal PaperHermetic.
USSR К42У-2 / K42U-2 Black Metal, painted greenPaperHermetic.
USSR К71-4 / K71-4 Black Metal PlasticMetallized polystyrene.
USSR К72П-6 / K72P-6 Black Metal PlasticTeflon and foil.
USSR К73-11 / K73-11 Black Wrapped plasticPlasticMetallized polyester.
USSR К73-15 / K73-15 Black Metal PlasticPolyester and foil.
USSR К73-15А / K73-15A Black Molded plastic PlasticPolyester and foil.
USSR К73-15В / K73-15V Black Metal PlasticPolyester and foil.
USSR К73-16 / K73-16 Black Metal PlasticMetallized polyester.
USSR К73П-2 / K73P-2 Black Metal, painted PlasticMetallized polyester.
USSR К75-10 / K75-10 Black Metal, sometimes painted HybridMetallized paper and polyester film, hermetic.
USSR К75-24 / K75-24 Black Metal, sometimes painted HybridHermetic.
USSR К76П-1 / K76P-1 Black Metal LacquerLacquer film, hermetic.
USSR К77-1 / K77-1 Black Metal PlasticMetallized polycarbonate.
USSR КБГ-И / KBG-I Black Ceramic w/ metal ends PaperHermetic. Flat radial leads.
USSR КБГ-М1 / KBG-M1 Black Metal, painted PaperHermetic.
USSR КБГ-М2 / KBG-M2 Black Metal, painted PaperHermetic.
USSR МБМ / MBM Black Metal PaperNon-hermetic.
USSR ОСБМ-2 / OSBM-2 Black Metal PaperNon-hermetic.
USSR ПМ-2 / PM-2 Black Metal PlasticPolystyrene and foil.
USSR ФТ-1 / FT-1 Black Metal PlasticTeflon and foil.
Wima White Dipped plastic, brown PaperVery brittle plastic, often cracked. Rounded square shape.

Note that except where transistions (from paper to plastic or hybrid) are known, my list generalizes; I assume that all of a particular type of capacitor use the same dielectric, based on only one or a few examples.

Again, I should state plainly that I am not encouraging replacing all paper capacitors; in many cases, especially with relatively late molded types, they can be left in place without problems. Rather, my main intention is to save myself and other technicians valuable time, effort, and resources by pointing out which types are plastic film and hybrid, and should therefore be excluded from recapping unless proven faulty. As well, where I've specified dielectric materials (based on official documents), my list may be useful for finding certain rare dielectrics, as well as knowing which paper dielectrics are impregnated with PCB oils.

If you have capacitors not listed that you are curious about, here are some suggestions. If you don't wish to destroy the capacitor, a reliable test can be done using Mr. Carlson's Lab low-voltage leakage tester. The design is only available on his Patreon page, and you have to build it, but it performs magnificently. The extremely sensitive "forecasting / mica" setting will almost always detect leakage on a paper capacitor, even some brand new ones. Yet, it will always show no leakage on a polymer capacitor, even those from the 1950s and 60s. Hybrid capacitors also nearly always show no leakage.

While the Carlson tester gives you a good idea of whether an individual capacitor is worth worrying about, breaking it open is the only way to be certain of what's inside. I find that squeezing between large pliers is sufficient to break away the shell of most molded plastic types, and metal cans can be pierced by flush cutters. Wear eye protection and disposable gloves, and work in a well-ventilated area, since you may encounter nasty vapors, possibly those containing PCBs. Once the shell is breached, the rolled layers can be cut with a blade and picked apart using fine tweezers.

From picking at the layers, you can easily discern the material. Paper is always translucent to opaque, and white to brown in color. It tears easily, giving a ragged fibrous edge. This is compared to polymer, which is transparent to translucent, and will sometimes stretch before tearing. When it tears, it does so in a clean line, or with some scalloped irregularity (if stretched to breaking), devoid of fibres. Most often, the dielectric will be easy to separate from the aluminum foil electrodes. Sometimes, the dielectric is "metallized", meaning it is coated in aluminum, comprising the electrode instead of a separate foil layer. It can be slightly harder to identify the material as a result of being unable to distinguish its color and opacity, but the same tests can be applied: stretching and tearing will reveal whether it is paper or film. Also consider that metallized polymer types are more common than metallized paper.

Below shows a metal-can paper capacitor cut open with flush cutters starting at the rubber seal. Note that the paper is brown, translucent, fibrous, and easily torn. This capacitor showed no leakage even on the "mica" setting of a Mr. Carlson tester, suggesting it might be plastic. No, it was just an especially good paper-in-oil. The paper was still noticeably wet; the rubber seals really did their job on this capacitor.

Below shows the inside of a 1950s polymer capacitor: a Good-All 600UE. This tested perfectly in both capacitance and leakage. Breaking it open, the film is very obviously plastic, since it is translucent blue, and stretches slightly before tearing cleanly and without fibres.

Lastly, here is a dielectric sample from a classic yellow-bodied "Blue Point" Astron capacitor, showing that it is hybrid. You can see the transparent plastic base layer, on top of which is a partially torn translucent paper layer. The plastic stretches and has no fibres, while the paper tears easily, giving a fibrous edge. Note that Astron Blue Point capacitors are one of several series that transitioned from plain paper to hybrid at some unknown point!

If you'd like to contribute to this list, I certainly welcome it, though there is a certain standard of proof necessary: either provide a scanned datasheet (or other "official" reference), or pictures of the capacitor both in unbroken and broken states. Here are a few types that I am especially curious about:

  • Astron Metalite in yellow molded plastic (and green or black text); these look nearly identical to "Blue Point" caps, but are almost certainly metallized paper.
  • Cornell Dubilier type ST "Budroc", a ceramic-bodied type. Probably paper, but don't know for sure yet.
  • Good-All types 623 and CMI-1. My suspicion is that both are plastic film, but I am not sure.

Links

If you notice any errors or have additional information that you would like to add, please contact me!


First Published: 12/30/2019