6H30's went into the 5900, not the 2900, and are not a replacement for 6DJ8/7308/6922. The 6H30 requires higher filament current, plate voltage, place current and dissipation than 6922. That said, if you have a 6H30 device, you can use the 6DJ8 type tubes, but not the other way around. I hope this was helpful.