LP70S

About the LP70S

The Conrad Johnson LP70S is a stereo vacuum tube power amplifier rated at 70 watts per channel into 4 ohms, using pairs of 6550 output tubes operated in ultralinear configuration for optimal power and low distortion. It features a three-stage audio circuit with a triode input amplifier, a cathode-coupled phase inverter, and a high-current output stage. The amplifier uses massive transpectral output transformers with intricately interleaved windings for extended bandwidth and high phase linearity. It employs about 12 dB of loop negative feedback to reduce distortion and achieve a high damping factor. The power supply uses discrete low-impedance DC regulators for the input and phase-inverter stages, polypropylene capacitors (no electrolytics), and a large reservoir bank for stable voltage. Bias adjustment is user-friendly with built-in LED indicators. The LP70S is known for its remarkable ability to reproduce the dynamics, textures, tonalities, and ambience of live musical performances, drawing on over three decades of Conrad Johnson research. It weighs approximately 80 lbs and measures 19" wide, 9" high, and 20.5" deep. The amplifier was produced in the 1990s and is considered a vintage high-end tube amplifier.