Cant blow up the schematic so I could only guess. Whatever the case
the cathodes can have high current at volume. Also note I can see no bias
adjustment. The other thing is HH Scott loved to make production changes
& without a visit to the factory it could be a challenge. The cats there
were always helpful & sometimes would run off an actual blue print !
BTW I lived & worked a few miles from the HH Scott factory. There were
piles of it in the area & had I known I could have had a barn full of it
for free or near so from the dump, yard sales etc. I would guess at the shop 75% of the mid to high end audio repairs were Scotties.
73 Zeno
LFOD !