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 Post subject: Waxed Paper Capacitors?
PostPosted: Feb Wed 13, 2019 3:08 pm 
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Joined: Mar Fri 27, 2009 8:57 pm
Posts: 521
Location: Alexandria Louisiana
When did the old waxed paper capacitor manufactures stop making them? Carl-Louisiana


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 Post subject: Re: Waxed Paper Capacitors?
PostPosted: Feb Wed 13, 2019 5:24 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 4465
Location: Charleston, W.Va.
Hi Carl,
I can't give an exact answer, maybe some others here can. But I know that some were still made as late as the early 1960s, or at least were still being sold by suppliers. By that time, very few were used in new-production radios & TVs. They had largely been superseded by plastic-bodied paper caps, which turned out to be just as bad (if not worse) than the older tubular waxed-cardboard paper caps.

NOTE: It should be noted that not every plastic-bodied cap from this era is paper. Some, including the Sprague "Black Beauties" with the red lettering, are mylar film caps and most of these are still just a good as anything you can purchase today.

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 Post subject: Re: Waxed Paper Capacitors?
PostPosted: Feb Wed 13, 2019 6:23 pm 
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Joined: Jun Fri 19, 2009 6:34 pm
Posts: 8265
Location: Long Island
There are two ways the question can be answered. The paper dielectric in typical tubular capacitors of the 1930s and 1940s was wax impregnated, then the wound foil/paper "slugs" were placed in cardboard outer tubes, end plugs with leads attached were inserted, then the assembly was sealed with molten beeswax or other types of wax under pressure. The cardboard outer tubes and beeswax gave way to plastic cases and dipped coatings in the 1950s. Internally, wax impregnated paper lingered on as the dielectric for some small electronics capacitors until the early 1960s before it was finally displaced by Mylar and other plastic films.

Prior to the development of waxed tubular capacitors, paper capacitors were usually enclosed in metal cases with pitch or tar filling. The tubular style of cardboard and wax cased capacitor (as part of a tone control for radios) was invented by Sprague in the late 1920s. The tone control didn't sell too well but the tubular paper capacitor from it was a huge hit and became their first major product. Micamold appears to be the first to offer small paper capacitors with molded-on Bakelite cases in the early 1930s. Solar Mfg. Co. offered "Sealdtite" plastic cased tubular capacitors in the 1940s. For reasons yet to be fully understood, the Micamold caps are nearly always bad today while the Solar ones often still test okay. Sprague bought the Solar line when the latter company went bankrupt in 1948, apparently to secure the Sealdtite patents, and a few years later introduced their "Bumblebee" line of phenolic cased, tubular paper caps. One of the major innovations in those was, the paper was impregnated with oil rather than wax.

Another Sprague innovation was "Di-Film" in the late 1950s. This is a hybrid paper-mylar dielectric which has the same characteristics as paper but much higher leakage resistance. It was a perfect replacement for paper-only dielectrics and was in production well into the 1970s. Metalized paper, which is a metallic film is deposited on a paper substrate has been around since the 1970s, maybe earlier, and is still in production today for applications where the superior surge resistance and long term stability of paper are superior to plastic dielectrics. Large power capacitors for industrial and utility company use are also often still made with paper.

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 Post subject: Re: Waxed Paper Capacitors?
PostPosted: Feb Wed 13, 2019 10:56 pm 
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Joined: Jan Thu 01, 1970 1:00 am
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Location: Perrysburg, OH, U.S.A.
Paper dielectric caps are still available: https://www.mouser.com/Passive-Components/Capacitors/Film-Capacitors/_/N-9x371Z1yzvvqx?P=1yznbzo
John

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