[Arran]

Quote: "It is not necessary to do this mod on sets with 5AR4, 84, 6X5, 7Y4 etc. rectifiers, as these tubes have a "heater/ sleeve" cathode arrangement, which are not likely to short." Actually it is probably more necessary, because one of the failure modes in a 6X5 is a heater to cathode short, the isolation can break down if the tube is overloaded. I've never had any problems with an #80 itself, in fact it's no unusual for me to run into a 1930s era AC set that still has it's original #80 rectifier. More often then not it's a short, or low resistance across the H.V line that cause the rectifier to fail, usually the input filter cap. I've also had HV windings develop shorts between the turns, particularly on early 1940s set with small transformers, presumably they were damaged in some way.
Regards
Arran