I scored some absolutely pristine 6AU5 (National brand) tubes at an estate sale. I put a pair into the (6AV5 wired) sockets of my G*S*G, and had a listen. They worked, but had an objectionable "gritty" sound. I am not talking "Golden Ears" gritty, it is readily noticeable. Considering how well the 6AV5 output tubes sound, I expected similar sound from the 6AU5 tubes. I cannot find anything by comparing both tube type's data sheet that would make me think they should not work. I believe the only difference is one more watt additional dissipation for the 6AV5 vs the 6AU5, and the smaller T9 envelope on the 6AU5's. Has anyone else tried using 6AU5 output tubes. I would be interested in your experience with them.
Thank you,
J.W.