Some possibilities, direct drive tubes, all in one bottle:
6B5
25B5
25/6N6
6AC6
Might be able to find the individual sections used in those in other bottles. But maybe these were tested for section match-up in the single bottle. Would have to check the datasheets to see if they satisfy the zero volt input grid to output cathode requirement.
Go to the head of the class immediately!! You must be an old guy like me.
For the 6AC6 I think you mean 6AC5. And the 25AC5 which is usually driven by a 6AE5. All cost too much now.
So I used a 6F6 much like a zero bias triode with G1 & G2 strapped together & found by experimentation that has a triode mu ~ 50. The driver is paralleled sections of a 6SN7. If you look at the triode mu of most audio pentodes & beam tubes they are in the range of 7 to 15. So the first triode needs to be meduim mu, the 2nd high. And all will look like a pentode.
I also did a 'Reach Thru' test on the 6SN7, refer to the attached. The measurement conforms 1/mu, nice to see for real!
But I did not do all this with the intention of building such an amp. I had long ago graduated from my slide rule & like any good HP employee I ran HP35, then HP67 & HP 71B with all the HPIL goodies. It was time to get some real simulation software so I bought Electronic Workbench Vers 5 to run in WIN95.
Curses, no pentodes, just any triode one could conceive of. And no obvious way to enter SPICE text files, sofar as I could see. What to do?
So I charged ahead & made my own models of pentodes using pairs of triodes. Just like we did here.
The other way round I use the voltage controlled voltage source for the triode & the voltage controlled current source for the pentode. All stuck to the proper plate rp.
