Email from Paul Reid 8-4-2015
I spotted Philbrick modules in a ribbon microphone featured in AUDIO magazine.
August 1965 (11MB PDF file)
A "New" Ribbon Microphone
page 19 (p21 in PDF)
schematic on 3rd page of article
"A1 is Philbrick P65 AU amplifier; A2 is Philbrick PP66 emitter follower"
The intent was to eliminate the double-transformer coupling (double losses) from ribbon to tube grid. A transformer is needed to couple the low-low voltage signal from the <<1 Ohm ribbon into any practical amplifier; the opamp gives gain and buffering so a transformer is not needed between line and recorder.
A major test-tool was "an antique harpsichord".
Apparently the Philbrick P65 can give a noise-figure of 1dB at 15K source impedance. Turns-ratio was 1:180!
Thought you might like this excerpt for the Archive.