i have an amp with a magnavox 6CA4 rectifier. i have noticed it "pings" when i tap the tube. also my power transformer seems to be running hotter than usual. when should a rectifier be replaced and do they have any effect on tone? i have read that some "sound better" than others. should i go for a high quality nos or use a current prodution? how important is this? i see them anwhere from 10 bucks to over 100 for a gold lion. is this just because of the rarity or is it really that much better? all other tubes in the amp are new. what is the story? thanks.