atmasphere 6as7g output tubes.

It's your amp and it's your money, therefore, as long as you are using the same tube type, knock your socks off and roll the NOS tubes.

The American 6AS7Gs can have issues, although we have found that the 6AS7GAs are the ones that are most problematic.

Here is what we know about the American tubes so far:

1) you get best results if your amplifier is a Mk3 or later.
2) If NOS, the tubes should be preconditioned for 4 days and 4 nights. This is done by placing them in the amp and putting it in Standby only for that time. If you apply B+ during that period the preconditioning process is ended.

Preconditioning can double the life of the tubes, help restore a better vacuum by activating the getter, and will also reduce the possibility of premature arcing.

BTW this process applies to all output tubes, assuming they are new/untested or NOS.

I would regard the use of American 6AS7Gs as experimental as you may run into premature arcing, but some customers have had excellent results. I think a lot depends on the tubes, if they are really NOS, that sort of thing. However- stay away from the GA varieties- they won't work.

I have the S-30. NOS tubes are essential, as they are for my Audio Horizons preamp. Finding the best tubes can take time and money. But once you do there is no going back.

If you want nice 6SN7s, we have gotten really good feedback on the Psvanes, Sophias and TJ Music tubes. This applies to the amps and the preamps.

Morgan Jones, he of "Valve amplifiers" fame, has written a piece on baking tubes that might be of use here. It's a variant on what Atmasphere talks about above, but using an oven to speed up the process of activating the getter flashing to absorb residual gas. Reductions in grid current are measured and found to be quite substantial, so long as you take care not to damage valves with phenolic bases.

Morgan Jones, Baking Valves