@drbond
My advice is to stay away from the 6080s on these amps! They are not built to the same spec as 6AS7Gs. The 6080 typically has a smaller grid heatsink and since the amp is biased in class A2, the grid can warp at higher power levels, causing the tube to arc- and often taking out multiple tubes at the same time. This won't damage the amp or speaker, but it can result in the user getting gun-shy and thinking there's something wrong with the amp when there isn't! Some people claim to have had good luck with 6080s but IME they've told me that while dealing in the same breath with failing tubes.
This advice extends to the 6AS7GA as well as any other variants. Stick to the 6AS7G. Now when dealing with American versions, if the tubes are NOS they will need to be preconditioned for *at least* 4 days and 4 nights in order to have any reliability. Otherwise the cathode coatings flake off and cause the tube to arc and fail. Of all the vintage types the Sylvania made examples hold up the best (and not surprisingly are the hardest to find).
So the Russian '6H13C' is the most reliable IME. If you use the Chinese 6N13 make sure its a military example such as seen with the 'PJ' suffix. The Chinese tube can develop what looks like a smoke ring on the inside of the glass; if you see this discard the tube (because the tube is failing and might arc). The Russian tube does not do that.
My advice is to stay away from the 6080s on these amps! They are not built to the same spec as 6AS7Gs. The 6080 typically has a smaller grid heatsink and since the amp is biased in class A2, the grid can warp at higher power levels, causing the tube to arc- and often taking out multiple tubes at the same time. This won't damage the amp or speaker, but it can result in the user getting gun-shy and thinking there's something wrong with the amp when there isn't! Some people claim to have had good luck with 6080s but IME they've told me that while dealing in the same breath with failing tubes.
This advice extends to the 6AS7GA as well as any other variants. Stick to the 6AS7G. Now when dealing with American versions, if the tubes are NOS they will need to be preconditioned for *at least* 4 days and 4 nights in order to have any reliability. Otherwise the cathode coatings flake off and cause the tube to arc and fail. Of all the vintage types the Sylvania made examples hold up the best (and not surprisingly are the hardest to find).
So the Russian '6H13C' is the most reliable IME. If you use the Chinese 6N13 make sure its a military example such as seen with the 'PJ' suffix. The Chinese tube can develop what looks like a smoke ring on the inside of the glass; if you see this discard the tube (because the tube is failing and might arc). The Russian tube does not do that.
