Posted by Damir [ 213.202.68.159 ] on February 12, 2005 at 15:27:09:

In Reply to: 6EJ7 posted by Tnuctipun on February 11, 2005 at 19:28:55:

You probably know this, but just in case... Amplification of the cascode is A=gm*Ra, just like in pentode, where gm is gm of "compound device, quasy pentode", or A~gm1*Ra , where gm1 is transconductance of the lower triode, IME - always gives a little "optimistic" values. With unbypassed Rk, gm1`~gm/3, and with Ra~8k2 - A~40.
Of course, there are "full" formulas for this ("Valve Amplifiers", RDH, "Vacuum tube amplifiers"). For complicated cascode versions there`s always SPICE (hey, I have EF184 pentode 3f4 model - if you feel desire for it...).
I also thought about cascode RIAA, but that Rout...

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