Tubes Asylum

Posted by Steve O (A) on March 14, 2007 at 16:32:42

In Reply to: Kinky posted by Chris O on March 14, 2007 at 12:19:49:

Not sure of the etymology but I believe Kinkless Tetrode is a British term for beam tetrode...and the 6L6 is most certainly beam tetrode.

The beam tetrode is another way to get around the nasty kink in the plate curves of a "real" tetrode, the pentode being the other means. See the image below (a 24A) and notice the region below about 100V where g2 voltage is greater than plate. It's a region of negative plate resistance. Maybe OK for RF but not so good for audio.

Compare this to the 6L6 below and notice almost complete absence of the "kink". At very low plate current there is some waviness in the curve but nothing like the real tetrode. I think some see the waviness and think it's the kink...but it really isn't.

Now compare to the KT66 below.

Pretty much the same thing EXCEPT,...notice how GEC conveniently chose not to plot the curves below 50V, the very region where the faint waviness of the 6L6 shows up. The waviness is there in the KT66 curve if the plot is continued.

One may prefer the KT66 over the 6L6 but it's not because the KT66 is kinkless and the 6L6 is kinky.