So I'm on AK and an update pops up in a JBL L19 mod thread. Here's the verbatim post, with my emphasis:
Er, AFAIK, and I think the JBL literature of the era backs this up, the cardboard tubed caps were mylar or polyester, of no particular fancy construction other than being wound, and then sealed for ease of assembly as "radial" standup units. I may grant that the capacitors would need to be hand soldered with extending wire leads but I cannot find any evidence that JBL's suppliers (usually sourced from US and Mexico, makes Chicago, IMB, Electro-Cap, etc.) used anything but plain tinned copper wire with common pvc or similar insulation.Originally Posted by ZOOM
I have a number of JBL crossovers and have examined the caps and their wiring closely. The wire insulation is very flexible and has a matte or flat appearance and a drag texture to it, indicative of thin PVC, not Teflon (TPFE) insulation which tends to be glossy in appearance and has a very slippery feel. Also, the original cap wiring is easy to cut and strip, while Teflon insulated wire is difficult to cut, even in smaller gauges. While the wire is quite silvery and shiny, I see no evidence of silver plated copper wire as would be found with Teflon insulation.
Although JBL was on the leading edge in terms of crossover knowledge and used mylar caps extensively from the late 50's on (probably the only speaker maker to do so), the advent of boutique capacitors was still not fully appreciated till the Jung/March article in Audio, circa 1978 or so, and still did not see wide use in crossovers for another decade. As for stacked film caps, AFAIK, they would have been made from mylar, they weren't widely available in the 70's and because of their construction, they don't offer a high volumetric efficiency for large values (above say 2uf). I haven't been able to find ANY stacked film caps in sizes above 2uf as their construction and use is primarily for PC board use. I suspect they would have been too expensive to build, purchase, and use, especially for values typically used in crossovers.
Another reason why the typical cardboard encased cap is not likely exoticly built or an exotic material is the simple fact that JBL would have touted their use in their product literature, consumer or professional, and discussed the merits of the type of material, construction, and use. JBL DID discuss use of bypass caps, eventual polycarbonate and polypropylene bypass in the 80's, as well as crossover topology when they were used on select models.
The last factor arguing against exotic is simply cost. Although JBL could certainly specify and buy in bulk and get the highest quality, even back then, costs mattered, especially in the consumer lines. It would make little sense for JBL to specify and use exotic caps in the L19/4301 at those lower price levels. The L100 of the early 70's used similar caps and the tech was even less known then.
Here's a couple of older threads which discuss the cap issue and thanks to mbottz for the helpful deconstruction of the OEM caps that look tubular and have no end plate as would stacked film types.
http://www.audioheritage.org/vbullet...l=1#post320369
http://www.audioheritage.org/vbullet...type-cap-is-it