Preamp characteristics:

Number of inputs: 4

Gain: 14dB

THDN: 0.2% , 20Hz to 22kHz

Noise: -94 dBu, volume pot at minimum

Preamp schematic

Power supply schematic

Input switching schematic

THDN test

Frequency response test

Noise sweep test

Power supply board

Tube wiring

Input relays

Chassis