[Arran]

 On these sets the 6X5GT, in and of itself, should not be a problem. The maximum plate voltages on this set, as well as the current loads, are well bellow the maximum ratings for a 6X5 tube, the plate voltage is somewhere around 180 vdc, and the set uses #41s which are the same as a 6K6 electrically. Can 6X5s wear out, yes, but in spite of the hysteria they are not the spawn of Satan that the ARF crowd carries on about if they are used correctly, and not incorrectly as in one of their saintly order of the big black dial sets. Now the output transformers are a known weak point in these sets, in fact in most 1939-42 Philcos with push pull output tubes, so check that.
Regards
Arran