Hello
Everybody think that all KT88 are the same . It is wrong . KT88 from Electro-harmonix do not sound much better than other one . You just have different screen current . Tubes with high screen current value may damage output transformers .It iseasy to check . You output transformers should always be cold .Never lukewarm .
To feinstei :
f the your digital ohm-meter reads 0, then the plate resistor has blown.... Sorry but no ! if the resistor has blown the voltmeter show OL (open loop) not zero . Zero is the lowest possible resistance value . When these resistors are bad you get no value , open in fact like a fuse will show !