I have a BT-1 preamp, EQ-1 RIAA equalizer, and 50 watt AMP-1 still in use from 1974. All built by the Quintessence Group from Sacramento. I switch the preamp out with a BT-2 from Audionics of Oregon circa 1980, still sweet! The EQ is especially useful as it was designed around the inflection points on the RIAA record curve. They are in use in my office system, main system is newer stuff.