[John L Stewart]

First of all, calculate the driver gain in grounded cathode mode from published specs-

For the 6SN7 family at 250 volts supply
Mu = 20
Rp = 7.7 K while grid volts is –8

Let A1 be the gain with these conditions,
Then A1 = ( mu*Rl ) / ( rp + Rl )
= ( 20* 27 ) / ( 7.7 + 27 )
= 15.56

Then find the maximum gain possible for any non-feedback triode stage-

Then A2 = mu
= 20

Gain change is A2/A1
= 20 /15.56
= 1.29

In DB becomes 20 log A2/A1
= 2.18 db

The feed back in the case of the bootstrapped driver is to the triodes anode, so no gain above mu is possible. There is no gain thru the triode being plate driven.

NTL, some experimenters have actually built working amplifiers this way using many triodes such as the 6S4 & 12B4. Starting digging, you will find them.

Hope this all mkes sense. Cheers to all, John