by Ty_Bower » Sun Jun 21, 2009 9:25 am
I have a couple quads of the 6CA7EH. The ones I have are clearly beam tetrodes. You can see the beam formers inside. They also have some minor grid issues. You can hear faint mechanical jingling coming from the grids while the amp is on. There might be a couple tiny spots on the screen where it glows a little bit. I'd also recommend you keep a watch on the overall dissipation, and keep it under 25 watts. Aside from these minor issues, they're decent tubes. They have a good sound that I like. From what you've written it appears you've already picked up on most of their details.
If you like beam tubes, you might also consider the Russian 6p3s-e (on the far right in the photo). Their prices have gone up recently, but you can still find a quad for less than $40 shipped. I'm not sure how they would fare in a ST70, as I've never tried them in one. I have run them wired ultralinear, with 450 volts B+. Keep the overall dissipation under 20 watts and they will be happy.
"It's a different experience; the noise occlusion, crisp, clear sound, and defined powerful bass. Strong bass does not corrupt the higher frequencies, giving a very different overall feel of the sound, one that is, in my opinion, quite unique."