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Originally Posted by andy
If you don't want to replace every paper cap, you need to get a cap tester that will measure leakage under full voltage. Sencore made a number of models which work well for that. I can almost guarantee that you'll find out every paper cap is bad. Not totally recapping a 50's TV is like restoring a 50's car and leaving the original rubber hoses, belts and tires on it. Sure, you might be able to get away with it for a while, but it will be unreliable and won't perform as it was desgined to.
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Yeah, I've got a couple of those capacitor testers (one Heathkit and one Knightkit), and I must say they're
really handy, since, as you say, they can test for leakage at full voltage. I've encountered high-voltage caps before that test great at 25V, but that quickly deteriorate once you get the voltage up past 100V. Usually it's a reasonably quick and helpful tool. In this particular case, though, the "bad guy" cap in question tested just fine at the maximum test voltage, so I didn't figure it to be the culprit. I guess it's just another reminder that test equipment doesn't necessarily reflect actual circuit performance..! I've also got one of those Sprague 'Quick-Check' testers that can check caps for opens and shorts even while in circuit.
As for the recapping philosophy, I can understand your point, and I realize that you're not alone in your opinion, but on the other hand, I'm not entirely sold on the analogy. Belts, hoses, and tires were always intended to be "consumable" parts on a car (take a look at what's not covered on the warranty of a new car!). I think a (somewhat) better analogy to completely re-capping a 50's TV would be that of replacing the carburator and fuel system along with the distributor, alternator, the wiring, and the rest of the electrical system on a 50's car all with equivalent components from a more modern car regardless of the condition or functionality of the original components. Sure, you may save some time and end up with a more reliable car, but one look under the hood will make the more modern replacements stand out and appear out of place. It's really a trade off, and one that I realize can be rather touchy and has its proponents on both sides. (Sorry!) On the one hand, I like to keep my vintage electronics close to as "original" as practical, but on the other hand, I also don't go so far as disguising modern components inside old shells (though I certainly don't have a problem with those who do). Since this set isn't intended to be a "daily driver", and I'm not in a big rush to finish, I think it's reasonable to try to keep things as original as is practical and safe. [If I was planning to run this TV for several hours a day, I'd be more likely to agree with your sentiment, but since I'm not...] Also, I tend to be of the "if it ain't broke, don't fix it!" mindset. Besides, if I just went and replaced everything wholesale, I'd miss out on most of the whole "troubleshooting" part of the project, which can be an educational experience all in of itself, even if it is frustrating at times.
Anyway, feel free to disagree!
PS: The chroma section of this set has very few paper caps (most of them are ceramic discs), and I've already tried replacing two of the more suspicious paper caps anyway, so I tend not to think it's a paper cap at fault in this particular case.