I would go for shorted turns on the "900" ohm one especially if heating and
knocking fails to show any variation. Shorted turns tend to be "welded"
together . I only have test data for the EL80 but 25mA per pentode and
looking at some Premier Tx data for range of use 7 watt to 60W, DC of HT
side ranging from 1500 to 16000 ohm so 4000 ohm seems more likely.
What is the physical dimensions of your ones?