marv
Strangely, very old equipment that has been used once in a while or frequently fares better than stuff sitting in an attic or barn for decades. I'd like to add to the list of potential keepers: Mallory.
Fusing is a great idea for protection against catastrophic failures.
It's easy and cheap enough to gut and stuff cans with modern electrolytics. NOS cans that have been laying around for decades are just slightly less likely to not respond to reforming than used ones. And even then, I wouldn't trust them to stand up to more than about 75% of their rated voltage.
In any case, if you find signs that the electrolyte has been seeping out the bottom, or there are are any perforations in the aluminum can, don't try to reform it. The whole can is poisoned, even if only one section proves bad. The rest are most certainly soon to follow.
The leaky old wax caps that have doubled in measured value need to be replaced, especially in power amplifiers where it tends to get a little toasty under the hood. You can melt the old ones and restuff the cardboard tubes with modern replacements which will be much smaller, and then use a little beeswax candle drippings to seal them up again, and nobody would ever be the wiser. Do a sanity check first, as this will not make the set play better. This type of restoration is a major PIA reserved for only the very best.
While you're at it, rewire with a grounded plug and lose the "death" capacitors, if any.
Bottom line, you can buy a fist full of capacitors for the price of one rectifier tube, or 5% of a replacement power transformer, or 10% of a pair of good output tubes. It's up to you.
:::Circa 1954 mono AM and FM tuners, preamp, power amp and Garrard changer in Chairside. Lots of multi section can caps. New available are pricey. NOS reformed are reasonable. I have a Solar CB, but is this always successful? What if I remove all tubes except rectifier, power up with Variac or lower voltages, monitor transformer primary current, and try reforming. Has this been tried before? Have not measured any values to weed out suspects. Suggestions??
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::I think reforming capacitors past the age of 20 years is just dreaming. Sure you can point to test equipment that is much older and still functional, but it's operating on borrowed time. Just yesterday I powered up a Tek 7000 series scope that had worked fine in the past; now it has a trace like a fish hook--probably bad caps. You have a 55+ year old Fisher? Just bite the bullet, gut the cans and install new electrolytics; then, you can stop worrying. Replace all the others at the same time.
::Johnnysan-
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:I hear you, and there are at least two opinions on this. The ability to reforming / use 'reformed' caps depends a lot on the quality of the original cap, and how it has been stored. (Attics where high temperatures are reached is bad.) I do not know what Heath used. Personally I have had good success with Cornell-Dublier, Sprague, and Aerovox; not good with Solar and Sangamino. Be aware that old / reformed caps may have less than the original capacitance. I sometimes disconnect the caps, and reform with an external source ( voltage source with 5K 5W series resistor.) With the cap removed, it is easy to measure capacitance and leakage current. I have 1940's car radios that work well with original caps (except I did replace coupling caps, vibrator cap, output plate to plate caps - the ones seeing the most stress where failure could do other damage.) I typically fuse everything with hidden fuses under the chassis. If I was repairing a unit for someone else, I would likely replace the caps. I have often cut cans open with a Dremel cut-off saw, put in new discrete caps, and glued the can back together with super-glue. It is difficult to see; or a thin band of shiny aluminum tape does not detract. As far as ALWAYS replacing ALL electrolytic and paper caps, it sort of depends on what the goal is. For maxium reliability, probably best to replace all (except maybe paper bypass capacitors that see low voltage, and already have a parallel resistor anyhow, such as cathode bypass.) If the radio is mostly for display and / or to enjoy 'playing' with, it can be a lot of fun to see how much of the original everything can be left. (But treat it like you would a lit candle). You have to draw the line somewhere, and most of us would be horrified with the thought of gutting a beautiful old tube set, and putting in a whole new solid state electronics. When for my own use, I get a lot of enjoyment out of keeping everything as original as I can for "good" performance and reliability. I am reminded of the woodsman who bragged that he was using an axe that once belonged to Abraham Lincoln; only it had gone through two new heads and three new handles. Ed M
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marv
:Circa 1954 mono AM and FM tuners, preamp, power amp and Garrard changer in Chairside. Lots of multi section can caps. New available are pricey. NOS reformed are reasonable. I have a Solar CB, but is this always successful? What if I remove all tubes except rectifier, power up with Variac or lower voltages, monitor transformer primary current, and try reforming. Has this been tried before? Have not measured any values to weed out suspects. Suggestions??
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:marv
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