Another little known late 1940's Gates preamp. Some mod notes on there too; one winding of the input trans secondary was not used, I changed the 6J7 plate resistor, and re-tapped the output connection. I've since discovered that particular ADC does not like to work in SE connection, but is meant for PP connection. Gates did a lot of things like that due to supply issues, I suspect. This amount of gain means you need a really well shielded input transformer, and this ADC would not meet modern needs for hum rejection when this power transformer is used on the same chassis. Before anyone suggests DC filaments, you can ground the 6J7 grid and it's very quiet. Very cool sounding unit; another I no longer own, but did for awhile.