For some reason, as I remove original caps, I like to test them just out of curiosity. Interestingly, the General Instrument caps were all good, no leakage. Virtually all the Cornell Duilier caps had moderate leakage (but not serious enough to keep the preamp from playing satisfactorily).
I replaced them all anyway, but I wondered what General Instrument did differently? Both brands appeared to be very similar in construction, at least from the outside.
So, I sectioned several caps with a hack saw. Both brands were similar in construction, with foil separated by a clear, thin dielectric material, something like cellophane or fine mylar (although I don't think mylar existed in 1960). Neither brand of caps used paper.
The clear dielectric material used in the General Instrument caps seemed perhaps a slightly heavier guage, possibly accounting for lower leakage.
Perhaps somebody who knows more about cap construction than I can shed some light on all this.
marv
:I just completed recapping a Dyanaco tube-type stereo preamplifier from about 1960. Most of the original caps looked like Sprague "Black Beauties," but they weren't. About half were Cornell Dubilier "Black Cats" and the others were manufactured by General Instrument.
:
:For some reason, as I remove original caps, I like to test them just out of curiosity. Interestingly, the General Instrument caps were all good, no leakage. Virtually all the Cornell Duilier caps had moderate leakage (but not serious enough to keep the preamp from playing satisfactorily).
:
:I replaced them all anyway, but I wondered what General Instrument did differently? Both brands appeared to be very similar in construction, at least from the outside.
:
:So, I sectioned several caps with a hack saw. Both brands were similar in construction, with foil separated by a clear, thin dielectric material, something like cellophane or fine mylar (although I don't think mylar existed in 1960). Neither brand of caps used paper.
:
:The clear dielectric material used in the General Instrument caps seemed perhaps a slightly heavier guage, possibly accounting for lower leakage.
:
:Perhaps somebody who knows more about cap construction than I can shed some light on all this.
I don't have a digital micrometer. If you do, email me your postal address, and I'll send you samples of the two dielectric films for you to mic. I can send samples from caps with the same voltage rating (400V), but their values will be different.
:Doug,
:1st: were the windings the same size for same value caps? 2nd: Have a digital micrometer, can you mic the thickness of the dielectric, which may be a clue. I would assume the thicker dielectric, if the same material would be less likely to be leaky. Were the dielectrics even the same mat'l?
:
:marv
:
::I just completed recapping a Dyanaco tube-type stereo preamplifier from about 1960. Most of the original caps looked like Sprague "Black Beauties," but they weren't. About half were Cornell Dubilier "Black Cats" and the others were manufactured by General Instrument.
::
::For some reason, as I remove original caps, I like to test them just out of curiosity. Interestingly, the General Instrument caps were all good, no leakage. Virtually all the Cornell Duilier caps had moderate leakage (but not serious enough to keep the preamp from playing satisfactorily).
::
::I replaced them all anyway, but I wondered what General Instrument did differently? Both brands appeared to be very similar in construction, at least from the outside.
::
::So, I sectioned several caps with a hack saw. Both brands were similar in construction, with foil separated by a clear, thin dielectric material, something like cellophane or fine mylar (although I don't think mylar existed in 1960). Neither brand of caps used paper.
::
::The clear dielectric material used in the General Instrument caps seemed perhaps a slightly heavier guage, possibly accounting for lower leakage.
::
::Perhaps somebody who knows more about cap construction than I can shed some light on all this.
:Doug,
:1st: were the windings the same size for same value caps? 2nd: Have a digital micrometer, can you mic the thickness of the dielectric, which may be a clue. I would assume the thicker dielectric, if the same material would be less likely to be leaky. Were the dielectrics even the same mat'l?
:
:marv
:
::I just completed recapping a Dyanaco tube-type stereo preamplifier from about 1960. Most of the original caps looked like Sprague "Black Beauties," but they weren't. About half were Cornell Dubilier "Black Cats" and the others were manufactured by General Instrument.
::
::For some reason, as I remove original caps, I like to test them just out of curiosity. Interestingly, the General Instrument caps were all good, no leakage. Virtually all the Cornell Duilier caps had moderate leakage (but not serious enough to keep the preamp from playing satisfactorily).
::
::I replaced them all anyway, but I wondered what General Instrument did differently? Both brands appeared to be very similar in construction, at least from the outside.
::
::So, I sectioned several caps with a hack saw. Both brands were similar in construction, with foil separated by a clear, thin dielectric material, something like cellophane or fine mylar (although I don't think mylar existed in 1960). Neither brand of caps used paper.
::
::The clear dielectric material used in the General Instrument caps seemed perhaps a slightly heavier guage, possibly accounting for lower leakage.
::
::Perhaps somebody who knows more about cap construction than I can shed some light on all this.
Dupont introduced Mylar polyester film in the early 50's, according to their website. Try to stretch the dielectric film. Mylar will stretch and distort, but the cellophane or paper film will break before stretching. At least this is what I found when dissecting capacitors.
I restore a lot of 57 Chevy Hybrid radios, and they have 2 caps that always test good on my Sprague T0-6 (must be Mylar), and also some other caps that always test leaky (probably paper/foil construction). Interestingly enough, in these radios, the Mylar ones are in waxed paper cylinders, and several of the leaky ones are in plastic casings.
Meade
:Yes, the dielectric film from each manufacturer seemed to have the same appearance, but I can't say for sure that they were made of the same material.
:
::Doug,
::1st: were the windings the same size for same value caps? 2nd: Have a digital micrometer, can you mic the thickness of the dielectric, which may be a clue. I would assume the thicker dielectric, if the same material would be less likely to be leaky. Were the dielectrics even the same mat'l?
::
::marv
::
:::I just completed recapping a Dyanaco tube-type stereo preamplifier from about 1960. Most of the original caps looked like Sprague "Black Beauties," but they weren't. About half were Cornell Dubilier "Black Cats" and the others were manufactured by General Instrument.
:::
:::For some reason, as I remove original caps, I like to test them just out of curiosity. Interestingly, the General Instrument caps were all good, no leakage. Virtually all the Cornell Duilier caps had moderate leakage (but not serious enough to keep the preamp from playing satisfactorily).
:::
:::I replaced them all anyway, but I wondered what General Instrument did differently? Both brands appeared to be very similar in construction, at least from the outside.
:::
:::So, I sectioned several caps with a hack saw. Both brands were similar in construction, with foil separated by a clear, thin dielectric material, something like cellophane or fine mylar (although I don't think mylar existed in 1960). Neither brand of caps used paper.
:::
:::The clear dielectric material used in the General Instrument caps seemed perhaps a slightly heavier guage, possibly accounting for lower leakage.
:::
:::Perhaps somebody who knows more about cap construction than I can shed some light on all this.
Film capacitors normally don't leak, but I have bought leaky polypropylene caps at the flea market, so nothing is impossible.
Probably my most useful handout from college engineering days is a magazine reprint from the 1950s on identifying plastics by burning a tiny sample in a match flame and noting the color of the flame, whether it melts and drips, smell, smoke produced and so on. Cellophane (though I never heard of it being used for capacitors) should burn cleanly, like paper. According to the reprint, polyester has a yellow flame with blue edges, and does not melt. A very thin sample might behave differently.
Film capacitors normally don't leak, but I have bought leaky polypropylene caps at the flea market, so nothing is impossible.
Probably my most useful handout from college engineering days is a magazine reprint from the 1950s on identifying plastics by burning a tiny sample in a match flame and noting the color of the flame, whether it melts and drips, smell, smoke produced and so on. Cellophane (though I never heard of it being used for capacitors) should burn cleanly, like paper. According to the reprint, polyester has a yellow flame with blue edges, and does not melt. A very thin sample might behave differently.
Film capacitors normally don't leak, but I have bought leaky polypropylene caps at the flea market, so nothing is impossible.
Probably my most useful handout from college engineering days is a magazine reprint from the 1950s on identifying plastics by burning a tiny sample in a match flame and noting the color of the flame, whether it melts and drips, smell, smoke produced and so on. Cellophane (though I never heard of it being used for capacitors) should burn cleanly, like paper. According to the reprint, polyester has a yellow flame with blue edges, and does not melt. A very thin sample might behave differently.
Film capacitors normally don't leak, but I have bought leaky polypropylene caps at the flea market, so nothing is impossible.
Probably my most useful handout from college engineering days is a magazine reprint from the 1950s on identifying plastics by burning a tiny sample in a match flame and noting the color of the flame, whether it melts and drips, smell, smoke produced and so on. Cellophane (though I never heard of it being used for capacitors) should burn cleanly, like paper. According to the reprint, polyester has a yellow flame with blue edges, and does not melt. A very thin sample might behave differently.
Film capacitors normally don't leak, but I have bought leaky polypropylene caps at the flea market, so nothing is impossible.
Probably my most useful handout from college engineering days is a magazine reprint from the 1950s on identifying plastics by burning a tiny sample in a match flame and noting the color of the flame, whether it melts and drips, smell, smoke produced and so on. Cellophane (though I never heard of it being used for capacitors) should burn cleanly, like paper. According to the reprint, polyester has a yellow flame with blue edges, and does not melt. A very thin sample might behave differently.