I just stumbled across the Turner Audio website. Lots of technical data related to building tube amps, solid state amps, speakers, etc. Also info on repairing/upgrading some older commercial tube amp designs. https://www.turneraudio.com.au/index.html
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I too have just found this web page. And I noticed they have a schematic for a phono preamp with active RIAA EQ that's very similar to the EAR834