It's a good idea to regard tubes that have red plated as being damaged until proven otherwise. Even if not completely failed, a prolonged period of red plating will likely change their characteristics, thereby potentially turning a pair that were reasonably well matched to a a pair that aren't. In such an amp, ie with a shared bias arrangement, tubes that aren't reasonably well matched will result in hum.
Try a 'known good' pair of 6V6 (that are a fairly good match to each other) in there.
What is the voltage rating of the HT caps? 7Vac doesn't necessarily mean they're bad, especially depending on how it's measured (p-p, rms, averaging).