Hi Chuck, You can see how Hughes Aircraft used to figure that on the bottom of this link: http://wc6w.50webs.com/wc6wamps/index.html?fr432.html 73 & Good morning, Marv WC6W -- "Partain, Chuck" wrote: I see a lot of formulae(is that plural???) on determining the output impedance of a tube. some say just plain plate volts divided by plate current, some have a 1.8 x formula and so on. I Want to determine this gu-84b impedance so I can start work on the tank setup. I run 3.9kv and I'm GUESSING 2 amp. I stuck a 2k in there and played some with the values so far and things look ok, no suprises. this is my motive for the question. lets hear some opinions! thanks as always. Chuck Partain http://home.comcast.net/~KA1MWP _______________________________________________ Amps mailing list Amps@contesting.com http://lists.contesting.com/mailman/listinfo/amps ________________________________________________________________________ Try Juno Platinum for Free! Then, only $9.95/month! Unlimited Internet Access with 1GB of Email Storage. Visit http://www.juno.com/value to sign up today!