[Arran]

Regarding short circuits between tube elements other then a rectifier I have never run into a short that caused catastrophic damage in a radio. Whenever I have encountered a shorted tube it's usually a short between the grids, which are close together, and somewhat delicate, on occasion a heater to cathode short, which causes hum, but that's more common in power output tubes in AC/DC sets, like a 50B5/50C5. Most tube failures are either open heaters/filaments, poor emission, gas, or the odd one can become intermittent.
Regards
Arran