6SN7 very common tube. If the set uses others swap them as a test.
If the vert is small but stable its usually a high ohm resistor. To test
you can nip one wire off & test.
Replace one thing at a time the try set before moving on.
Keep filter cans were they were in the set Mount a terminal strip for them
enuf fer now
73 Zeno
LFOD !