germanium line amp, modify for variable gain?

[abbey road d enfer]

by incresing the open loop gain you can have a lower input impedance than 600 ohm, that're the nominal impedance of this amp.
Obvius, it can run with the actual gain the same (and infact it runs), but who would want to have a "more active summing amp" from this stage can use the bootstrap, just a my modest idea 

I agree 100%, but in the context of the era, I think the idea of putting to market an amplifier with ca. 65dB gain and an input Z of 60r was somewhat too advanced. Many mixers were built according to a cookbook; terminating a mixing network into such a low impedance was too exotic. And so much gain was certainly bound to be noisy, eh?

but in this case using 22k- 47k res on summing net the closed gain is only a bit more than without bootstrap so the noise is not increased pratically. 

That was a sarcastic comment. Many technicians of the era swore that such a large unmatching of impedances was devilish, and they believed that gain equalled noise. I had a technical director in the early seventies who explained me that opamps could not be used in audio, because their gain and input impedance were too high...