Your tubes are deading and you need to retube(try the new WE300B and you will like it better).
Hello, This is Darrin at Audio Limits.
I would have to say that it is time to replace the tube's.
edle is correct in recommending the WE 300b's they are incredible however charlie has stopped production on them as they are moving the factory into Alabama. we should be receiving 100 pairs hopefully by next month if you are interested. at this time they are very hard to find new with warranty.
my experience with Western Electric 300bs in my VAC 70/70 was just OK, nothing special. I think it really depends on the circuit that is using the 300b. The VAC is not the ordinary 300b amp. I've tried Western Electric, Golden Dragon and JJs, and the JJs were by far the best. A nice big solid sound, with plenty of detail and energy. I got a matched OCTET at eurotubes.com for under $700! definitely worth it!