PrimaLuna ProLougue Four EL34 Power Amplifier March 2021 This is the PremaLuna ProLogue Four (PL4). Its a zero feed back, enhanced ultra linear, class AB Push-Pull Amplifier. 35W/channel output. I got it to power my Mid/Twt drivers, so it's circuit and tube complement are not concerned with Bass reproduction. As such, its EL34 tubes, renowned for their sweet midrange, are a good choice. My Bass drivers are powered by a Nord Class D amplifier 700w/4ohm. The full compliment of Tubes, in sequence (per channel) are: x1  12AX7  Driver Tube x1  12AU7  Phase Inverter x2  EL34 Power Tubes in Push-Pull configuration. Its a great sounding Amp, with a quite background. Its unique feature, is PrimaLuna's Adaptive AutoBias Circuit. No need to purchase matched tube sets or fiddle with settings under the hood to adjust the tube bias, just buy new tubes, fit and forget, the circuit automatically monitors/adjusts the bias, to run the power tubes in their optimum window.