[Amps] Blocking capacitor drift

[Peter Chadwick]

My experience with ceramic caps of this sort is not so much drift in capacity as apparent upwards drift in loss. Even if a coupling capacitor did drift in capacity, as Tom points out, you wouldn't really notice. Loss is another matter, especially for padder capacitors carrying a lot of current. If you keep the juice on for long enough, all sorts of interesting things happen, usually, I find, with bits becoming unsoldered internally, and the thing falling apart with  a smell of burnt paint, a few arcs and flashes and bangs and hopefully, the breaker or fuse pops before you have an expensive tube damaged.
The other point is that at least in my experience, once a ceramic cap decides to start getting hot, that's it - it is at the end of its life.But very often, I've found, at low current levels, it appears fine, so measuring on a Q meter may not show a problem.
73
Peter G3RZP