The 68 Custom Deluxe Reverb I purchased a while back remains my favourite amplifier. I've kept the original 6V6 Groove (JJ) tubes and have no issues with them. There are no rattles and the amplifier sounds really good. I've changed the pre-amp tubes but that's it. A fellow I know and trust has some NOS 6V6's I can get at a "real deal" and he's offered to bias the amplifier properly for them as well. I have to admit I'm intrigued based on things I've heard about good NOS tubes. I don't want to fix something that's not broke and I know I can always reverse things. My question, have you had any personal experience, good, bad or meh, using NOS tubes? Besides tone, I'm concerned about the reliability. From what I've read if they are good NOS tubes they are more rugged than new tubes...but I can't say I know that to be a fact and I use this amplifier a lot at varying volumes. Any comments would be appreciated.