[35Z5]

A resistor in the heater line should not blow, reguardless what you've disconnected on other pins. Requires a major short. 

Operating, the total current draw for tube elements is roughly 70-80 ma, by far most of that is the pair of 50L6 audio outputs. The 25Z6 operating with elements in parallel can safely supply maybe 150ma, above that it's in failure mode. The purple was either a severely overloaded tube or it catastrophically failed by it's own accord. 

By chance were you using the 25Z6 that was previously overloaded?  


My Birdie is still in pieces, maybe one of these days.