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Adding a line fuse and strategically-placed B+ and/or cathode-circuit fuses (pigtail fuses hidden under the chassis with clear heat shrink tubing slipped over them, for example) tends to minimize risk of catastrophic failures, even with some marginal capacitors left in place. What I typically do is add some safety features and as much preventive recapping as my clients are willing to pay for, which tends to vary somewhat. For items in my private collection, I add safety devices and perform needed repairs first, then recap as preventive maintenance as time permits. Some years ago, tubes were rated with TWO sets of ratings, designated "CCS" for "Continuous Commercial Service" and "ICAS" for "Intermittent Commercial/Amatuer Service" and many of the devices we AK members restore are actually transitioning from the continuous use for which they were initially designed to intermittent use.
Paper capacitors which show visible signs of "hot spots" (bubbles in their wax coating) and those which are responsible for crummy performance and/or out-of-spec readings during a check of tube pin voltages are the first ones I replace. Any significant change in the set's performance is a sign to me that it needs to be inspected more thoroughly at some point, and I've had good results with having adequate advance warning of performance issues. Anything from a sudden onset of touchy sync to a blown fuse will get a set in my collection tagged for a trip to the workbench at my earliest opportunity.
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03-04-2007, 07:01 AM
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