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.
