The standout that got my attention was the RCA 41-B (1934), several threads and the manual is in the tech docs. ruffrecords pointed out the Pultec MB-1 is as well, though for purposes of DC coupled NFB gain control; unique. This came up in a thread about the Collins 6R, in which case it's of minimal ratio, and relates to a current meter connection.
What else have you spotted?
RCA 41-B - barely predates recognition of NFB as a method, and when you consider the very small capacitor and lower transformer inductance values, probably several other things going on as well.
Pultec MB-1 - DC coupled NFB gain control from a cathode follower
Pultec SP-3 - similar to above
Collins 6R - small ratio combo related to cathode metering
Collins 6P - small ratio combo related to cathode metering
What else have you spotted?
RCA 41-B - barely predates recognition of NFB as a method, and when you consider the very small capacitor and lower transformer inductance values, probably several other things going on as well.
Pultec MB-1 - DC coupled NFB gain control from a cathode follower
Pultec SP-3 - similar to above
Collins 6R - small ratio combo related to cathode metering
Collins 6P - small ratio combo related to cathode metering
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