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What are these caps good for?

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I have acquired several NOS Sprague capacitors( I'm guessing '70s-'80s) and am curious to know what they are best suited for.

There are:

Orange Drop 4PS, 6PS, and 10PS radials.

Black Cat PKM electrolytics.

Atom TVA electrolytics.

A plain aluminum electrolytic that has 30D and then a TE-**** number.

Thanks for any help.
I would throw the electrolytics away. The Sprague orange drops may be paper/mylar or all mylar depending on the date. Generally the dull orange ones are paper/mylar and the bright orange ones are all mylar. Look under the cap between the leads and if you see an opening then it is dipped. If so it is most probably paper/mylar. The paper/mylar were produced well into the 70s and possibly into the 80s. The bright orange (all mylar) ones are still made by SBE and they are powdered and baked, not dipped. They are a very bright orange.

The 4 means 400V etc. The PS was originally the “replacement line” when TV shops re-capped a radio, TV, etc. They were reliable and cheap replacements for the leaking beeswax/paper caps. They were first produced in the early 60s as I recall.

The Spragues are not bad because they have an impregnant that is stable. They are actually highly sought after vintage caps for guitar amps. They have the “60s sound.”
Many claim that the sound of a paper cap is due to the leakage taking the grid out of the linear region. Well, all of the old circuits built with the paper/beeswax caps were probably designed for a little leakage. The sound of paper in the cap may be paper dielectric distortion, but it is vintage.......as in late 60s psychedelic rock.

The impregnant in the paper caps that go bad is beeswax. The impregnant in a Vitamin-Q is a polymerized oil. This is why the Vit-Q doesn’t go bad.

The PS were originally called “difilm” because of the two dielectrics (paper and mylar). The very early ones were series 220 (written on the cap). All PS use a solid impregnant. I have a lot of them and none of them have shown up as bad. The impregnant is used to fill in the holes in the fibrous paper.

The paper/mylar PS series have a very small amount of normal leakage (a few microamps). This is harmless. Most of it is due to dielectric absorption. I talked with a Sprague engineer a few years ago about this and also tested some at 150% of rated voltage. The leakage goes to zero at this voltage. This was a micro-amps test with two 400VDC variable power supplies in series.

The Black Cat is of similar paper/mylar dielectric, but each company had its own “proprietary” impregnant and some of them go bad and have dangerous leakage. EM-Arco (chocolate brown) and Sprague caps are stable. I recall testing a Black Cat and recall not liking what I found, but not sure. Many of the metal can paper caps are also bad so don’t assume a mil-spec paper cap is still good. 396 with a quadrajet? Mark
Mark, Wow! Thanks for the detailed info. Some, if not all, of the Orange Drops are Difilm. I have the original plastic flip open cases they came in new. I was basically wanting to know if any of these were anything special, as far as use in audio and PSU circuits. I'm sure there are several versions, but I have heard "Orange Drop" tossed around for years, but have never really used any. Since I got them at no cost, I figured I'd check and see what I have, and see if they are worthy of use.

My 396 actually has a Holley spread bore, which replaced a Quadra-Jet before I owned it. Several years ago I replaced the Holley with an Edelbrock Q-Jet carb, but didn't like it. I have a Holley 750 DP and new intake to install, but have never taken the time to do the deed.
Difilm on the box makes the issue quite clear. The electrolytics will leak unless reformed with a voltage treatment. It is more practical to buy new ones from Mouser or other big distributor that has brand new ones on the shelf.

The DoublePumper (mechanical secondaries?) is a touchy little machine in my opinion. For street use I prefer the vacuum secondaries which can be calibrated to open as required by the rest of the hopefully tuned-up engine.

If you had the QJ then I was going to say that they need a liberal coat of permatex on the air horn because they usually leak there and won't tune.

Good luck with you muscle car. Big blocks have such large ports that they require a good ear to tune, IMHO. The 454 was next to impossible. They don't like the conversation to steer away from tubes so I will stop peeling out now. Mark
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