atmasphere 6as7g output 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.

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.

Sabai, you may be confusing the driver tubes (6SN7s) with the power tubes (6AS7G). I've been doing this a long time- I don't know if I have ever even heard of Mullard 6AS7Gs.

I would like to know if anyone has compared the Sovteck to the RCA 6AS7G's and what their finding were?

Sure- in our circuits the American tube makes more power and is less reliable. This is particularly true of the GA variant which should be avoided entirely due to being particularly unreliable.

This is no small amount partially due to the fact that we employ a fixed bias scheme rather than self-bias. The American RCA is not spec'ced for fixed bias operation while the Russian (and Chinese) tubes seem to have no problem with this. But we have also found that the American tubes hog current more easily (which is why we suggest that they only be used in our gear if that gear is a MkIII series or later). In addition, the GA variant has a smaller grid heatsink, and since we employ Class A2 operation (where grid current can flow during part of the AC waveform at full power) the grid of such tubes can warp easily and cause an arc.

So we recommend if you want the best reliability, to use the Russian power tubes.