>Actually, most all tetrodes today have a suppressor grid, but it is connected to the cathode internally, and is not externally accessible as it is with most tubes called pentodes. Additionally, only tubes classified as tetrodes today have beam forming plates.

No. In fact, I never see any currently-made "tetrodes" or "beam tetrodes" with suppressors. Such tubes appeared occasionally in the past, usually due to laziness or mislabeling. And I often see data sheets and other info calling 6L6 types "power pentodes" and EL34s "beam power tubes". It's a common error. Not helped by the existence of genuine beam-power versions of 6CA7s, such as the one Sylvania made in the 1970s/80s. (New Sensor is working on a new beam-tube "fat bottle" 6CA7 right now.)

>Generally speaking, cathode bias yields a more musical sound, while grid bias yields more power.

That's too debatable. Cathode bias produces slightly lower efficiency and higher distortion. I still regularly encounter guys who hate cathode-biased SE or PP amps--"too mushy sounding". Leave the personal choice to the user, I'd say. It's safer.

>Among popular types, these include the 6L6GC, KT66, KT88, 6550, 6CA7, 6BG6, and EL509/6KG6, to name a few. Popular pentodes include the EL34, EL84, and SV83. Popular indirectly heated triodes are the 6AS7 and the cult favorites, the 1626, 12B4, and the unusual 6C33. Directly heated audio triodes include the 2A3, 45, 300B, and transmitter style triodes like the SV-572, 211, 811, and 845. Almost all commonly used small signal tubes are triodes, with the exception of perhaps the EF86, which is a pentode.

Some of these tubes are dead issues. I would leave out the EL509 as a "popular type", as it never was very popular. The 6BG6 is defunct. The SV83 is still available from New Sensor but I can count the number of amp mfrs. using it on (half of) one hand. The SV572 is probably dead also, when New Sensor gets rid of the remaining stock I seriously doubt they will get more made. And I'm pretty sure the EF86 is not made anymore, because that was a Svetlana-Malevishera product and I don't think they are making anything but 300Bs there now. They also used to make a pretty good ECL82 and the 6D22S. I doubt those have much future.

I have been TRYING to write accurate articles about audio tubes for WIKIPEDIA. The few articles on Wikipedia about vacuum tubes were total crap in the past.

Wikipedia has major problems, not because there's a shortage of experts, but because that thing attracts mostly young computer nerds who want to talk about what interests them--Star Trek, Star Wars, Buffy the Vampire Slayer, Tolkein, shoot-em-up videogames, obscure alt-rock bands, etc.

You should see the Buffy listing on Wikipedia. Hundreds of subpages for every minor character that ever appeared on that well-written-but- kinda-silly cult show. Which was canceled last year, btw. But I had to REWRITE the short listings for "vacuum tube", "thyratron", "Nuvistor", "nixie tube" and several others--because they were incoherent, error-filled garbage. Computer dorks don't know a damn thing about any electronics that came before Atari Pong. But they do like to talk about Buffy...

vampires don't count as a major social problem, ignorance does!

Go to wikipedia.org and look up KT66, for example. I wrote it. Did you know that RCA didn't actually invent the beam tetrode, they licensed the design from M-OV? Because M-OV didn't think they could manufacture them in quantity. AFTER they saw the success of the 6L6, M-OV came out with the KT66......the references are listed there.

For that matter, anyone can write and post a Wikipedia article. You experts on here should post articles THERE. Don't waste your writings on a forum, post them somewhere that lots of people will see them! It is becoming a very popular place for people to do research--in spite of the lack of editorial oversight! You can help fight off misinformation, AND have a ready source of FAQ for linking to, by putting it on Wikipedia. Just a suggestion...