Larry,
I can tell you one thing: If you have the 6c45 tube, you're stuck with it. I tried the 5842's, and they don't work. I need to research tube specs to find something that I can sub for the Russian tube.
On the other hand, if I keep the gain switch on low I have all of the volume I need (which can sometimes be quite a bit) with no tube noise at all. They get a little microphonic with the gain set to high at higher lisening levels.
I think it is a very good tube, but I wish I had some more choices. It is fun using tubes as "tone controls" and different sounds. I had all kinds of fun when I was playing around with the 12ax7's in the Audio Note. I'll keep looking, and let you know....