:Replace 'em all including the electrolytics and don't power it up until you do.
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:You will probably find the resistors have all migrated up, and for a nickel each, replace 'em. As fo the silver micas (dominos,) it's a crap shoot. I no longer wonder, just replace them with fresh stock. Include those hiding insode IF cans, if any.
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:The prevailing school of thought on this forum is replace . replace .. replace. Not a bad thing for a fancy or high end radio. But I do not want to discourage new-comers to the hobby, and in some sets, to get to all capacitors, one has to do much disassembly. Also, unless one is careful, experienced, and sometimes just lucky, sockets and switches can be damaged. There are other schools of thought. One school might be to keep everything as original as possible, which might include putting new caps inside the old capacitor cases. Another school might be to replace only what is likely to hinder proper operation of the radio, might be consevatively expected to fail, or where failure could take out tubes, transformers, or other items. It might depend on what you are going to do with the radio after it is repaired / rebuilt. I encourage those who like to work on old radios to learn as much about radio history and how circuits work as possible; books from the 40's can be found in the internet at reasonable prices - any radio club can make suggestions. Technology was not the same during the golden age of radio as it is today, and I respectfully suggest that it is far too easy to measure yesterdays technology by today's standards. (Or to be part changers.) Many of the old paper capacitors had 'leakage' when new; much of the test equipment of the era was not sensitive enough to measure it. ALL modern aluminum electrolytic capacitors have some leakage - it is specified in the data sheet. (A capacitor with no leakage, if charged up to rated voltage, laid on the table for a week not connected to anything, will still be charged to that voltage a week later.) Some manufacturers actually graded the old wax paper capacitors, using the best ones in audio coupling or AVC circuits, and the more leaky ones in cathode or screen bypass circuits, WHERE LEAKAGE ABSOLUTELY DOES NOT MATTER, unless you have a really BAD capacitor. Manufacturers used 600 volt capacitors in 200 volt circuits, not because they needed the voltage rating, but because they had thicker paper or more layers of paper, and therefore less leakage. Resistor values were often used by convention (such as the 220K or 470K resistor to the plate of a 12SQ7), and in most applications could vary by plus or minus 50% or more, and not affect the operation or reliability of the equipment. In fact early 'dogbone' resistors were manufactured and used with a perfectly acceptable plus or minus 20&%. So I suggest, that for most applications, all electrolytic capacitors should be replaced, all paper audio coulpling capacitors should be replaced, maybe any paper caps in an AVC circuit; any discolored resistors are suspect, but leave ceramic, molded mica, and paper screen and cathode bypass capacitors alone (these units are typically shunted by a resistor of much smaller value than the leakage resistance, so the whole point of leakage is moot.) Ed M
::::I am repairing a Halicrafters S-108 radio, it has all Cornell Dubler plastic capacitors it it, how reliable are these units? If they were paper/wax units I would replace them all, as I have had nothing but bad luck with these old type of caps, what would you do?
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:::Depending on the type of capacitor, they may be plastic on the outside, but just a lousy paper capacitor on the inside. I would not trust any capacitor of that age without testing for leakage; many types I won't even test because it's a waste of time.
:::Johnnysan-
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:::You were sure right! I tested 4 of these caps and all had severe leakage, I woun't even waste the time to check the rest, just replace them all.
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