[Arran]

 In a restored set I have very seldom had any problems with tubes, didn't seem to matter whether it was a series string AC/DC set or a transformer type. In an AC/DC set if a tube blows something, like the heater or a cathode, there is usually an external cause like a heavy current load. I've bought sets that had tubes with an open heater but I've never had one fail in service once I overhauled the set. In one case I had the 35W4 die in a Canadian Pye radio, but I bought that set as working, the previous owner recapped it other then the audio coupling cap between the 50C5 and the 12AV6, but since I never checked the tubes it may have been on it's last legs when I bought it. In the other case of a tube going bad it was also a 35W4, but in this case it was the cathode connection that popped, the reason being is that the 50C5 was loose in it's socket and kept cutting in and out of circuit whenever the radio got bumped, it ran fine as a daily driver for ten years before that though.
 As for AC tubes, I've never had a rectifier fail whilst in service, in fact many of the sets I get still have the original rectifier tube in place, sometimes worn out but often they are fine. In my latest restoration job, an Electrohome, it uses a 6X5GT, the strange part is that one diode tests fine but the other tests weak, and it is clearly a replacement since the original would have been either a Westinghouse or a Marconi brand tube not a Rogers. The set still had it's original filter caps in it, so that may explain why the 6X5GT was replaced with the Rogers one and why it's weak on one side. On the other hand the 6K6GT that sits next to it appears to be an original, and tests quite strong, the 6SQ7 that drives it seems to be borderline.
 From what I can tell this was a set with a high number of hours on it, or at least medium high, every resistor is either drifted or open, the 6SA7 is a Japanese GT style replacement, and someone stuffed a 6SJ7 where a 6SK7 should be. It could be that the original 6SA7 may have died due to a lightening strike, as the B.C band antenna coil was burned up, but 6SA7 tubes tend to be driven hard anyhow since they act as an oscilator-mixer and first detector.
Regards
Arran