Allow me to explain some things. Most "beamie tubes" I see nowadays that are classified as "tetrodes" have an internally connected suppressor grid illustrated in their pinout diagrams. Correct me if that's not so in reality. I've never had the nerve (money?) to bust open a $40 KT88 and find out! I too, see 6L6GCs labeled as "power pentodes" and EL34s (not 6CA7s) labeled as "beam power tubes." Are the pinout schematics of the "beam tetrode" KT66, KT88, 6550, etc, equally misleading? Is there a suppressor or no?

Your point about the musicality of cathode bias is well taken. To each his own. I was speaking from personal experiences, and guess that experience can't speak for everybody. Most every serious DIY'er I know, including myself, prefers cathode bias though. I suppose it's like DHTs. I know people who HATE the 300B sound, and others who will have nothing else. My personal taste for the 300B is a mixed bag. I do enjoy and appreciate the "warm honey euphonic 300B sound," but really prefer the less syrupy sound of 2A3s.

I probably shouldn't have listed some of those as "popular types." I simply meant that they were indeed used somewhat, albeit not on the scope of EL34s! I should have listed the 6BG6 under the "cult tube" heading, as this is where it's usage is seen.

I regret to hear that the SV572 stock is uncertain. Although it enjoys a strong following among DIY extremists, I guess it never took off in the way they had hoped. I REALLY regret hearing the Svetlana EF86 is not being made! I have a few examples of some old "S" logo tubes, and IMO they are one of the best sounding small signal tubes I've ever heard when configured as a triode.

Long ago I built a customer a simple SE EL84 amp with a triode configured EF86 driver, and to this day it remains one of the most musical sounding amplifiers I've ever heard. I recently saw some "winged C" EF86s. I presume by your post they are, but are these the same tube as the older "S" logo, and not new production?

Thanks for your take on the 6L6 and KT66. I had read the story I had posted in two or three places, and took for granted that it was accurate. I had read that MOV was having difficulty with inventing a way to accurately align the screen grids in an expedient way and gave up, as you had said. But, the articles I had read said that it was RCA who had came up with a beam tetrode first, and then MOV went into high gear later when they saw the 6L6's success.

Thank you for your insight, experience, and stellar knowledge of all things tube. It is much appreciated. I've been servicing, modding, and building tube gear as a hobby and part time income since the mid 80's. I've learned a great deal over time, but still have nowhere near your vast knowledge and experience. Maybe someday........

Thermionic :)