This is my SRPP linestage preamp based on the 6SN7, the Hong Kong-built BEZ Model Q4B by Edmund Lam. With all NOS tubes: '50s RCA 6SN7GTB blackplates, gas-regulators also by RCA (1958 OC3 and a 1967 OD3), and a NIB '50s Mullard GZ30 rectifier. With nothing but a 23-step attenuator and a 3-selector switch, it's simplicity all the way around that sounds great!