ampllifier design

The 6DJ8/6922 family of tubes, which includes the Russian 6H30 extension, are not designed for audio, and while quite linear, tend to have a microphonic signature that is considerably more pronounced than in other tubes designed for audio, like the 12A* series, 6SN7 or the like. The 6CG7 is the same thing as a 6SN7 but in a miniature style package. It tends to have more microphonics than the 6SN7 does as a result.

Although less efficient, power triodes otherwise will run circles around the best pentode power tubes in every way, including longer life.

Hi Jimjoyce25- bingo! We got great linearity out of them, but they would often ring like a bell. Handpicking them got the microphonics down, but never to the point that you can get with a 12A* series tube or 6SN7. I'd always been a fan of the 6CG7, but when I realized that it and the 12AU7 were evolved from the 6SN7 geometry, I decided to try the 6SN7. There was no looking back at that point.