03-03-2013, 01:23 PM
Antique paper caps are regarded as the most failure-prone radio parts other than electrolytics. They are prone to fail both suddenly and gradually, and when they short, they can burn out parts that are difficult to replace, such as IF and other coils.
Orthodox radio restoration advice since the '80s has been to replace all 'lytic and paper caps during a restoration, and with good reason. Not that modern caps can't fail, but they are far less likely to, since they are new and are of far improved technology.
My personal experience is that at least 75% of paper caps leak at rated voltage, which to me means their intact cousins will do so soon. I'd go ahead and replace them wholesale. By the time you've made the effort to test them, it's not that much more difficult to replace them all.
Unfortunately, replacing paper caps in those '38 to '42 Philco sets could disturb the brittle rubber wire insulation, requiring replacing or reinsulating that wire as well. But hey, it just adds to the fun and to the pride of completing a robust restoration to better than original standards of reliability.
Orthodox radio restoration advice since the '80s has been to replace all 'lytic and paper caps during a restoration, and with good reason. Not that modern caps can't fail, but they are far less likely to, since they are new and are of far improved technology.
My personal experience is that at least 75% of paper caps leak at rated voltage, which to me means their intact cousins will do so soon. I'd go ahead and replace them wholesale. By the time you've made the effort to test them, it's not that much more difficult to replace them all.
Unfortunately, replacing paper caps in those '38 to '42 Philco sets could disturb the brittle rubber wire insulation, requiring replacing or reinsulating that wire as well. But hey, it just adds to the fun and to the pride of completing a robust restoration to better than original standards of reliability.
John Honeycutt
