7404 and 5691 tube available or substitute?

For the 7404 I found this on Google
http://www.google.com/search?source=ig&hl=en&rlz=&q=7404+vacuum+tube+equivelent&oq=7404+vacuum+tube+equivelent&aq=f&aqi=&aql=&gs_sm=e&gs_upl=5927052l5943795l0l5945101l27l27l0l20l20l0l346l1950l2-6.1l7l0

For the 5691
http://www.google.com/search?source=ig&hl=en&rlz=&q=7404+vacuum+tube+equivelent&oq=7404+vacuum+tube+equivelent&aq=f&aqi=&aql=&gs_sm=e&gs_upl=5927052l5943795l0l5945101l27l27l0l20l20l0l346l1950l2-6.1l7l0#sclient=psy-ab&hl=en&source=hp&q=5691+vacuum+tube+equivalent&pbx=1&oq=5691+vacuum+tube+equivalent&aq=f&aqi=&aql=&gs_sm=e&gs_upl=7704l8419l1l9537l4l4l0l0l0l1l197l633l0.4l4l0&bav=on.2,or.r_gc.r_pw.,cf.osb&fp=63d36238f7bf8551&biw=1152&bih=734
Looks like several to choose from

Thanks for the help. I feel pretty dumb on this one. apparently the 7404 is the production date in this tube. It is an RCA and looks like its from the 70's. I have been told that this tube is actually an OC3 voltage regulator tube. Does that sound correct?
Thanks

I'm not familiar with Cary. Nor am I a tube expert. In fact I got my Octave about a year ago and am trying to learn more about the tubes I can use. Just google it. I responded to your question because I would hate for someone to think they have to retire a tube amp because of availability of a tube.