6J1 still has good linear performance and working state even when voltage is lower than 50V. So supplying AC12V low voltage and boosting voltage to 28V can greatly extend the amplifier lifetime and increase SNR; DC power supply can use cheap components, which are easily to be purchase; No need expensive and large high voltage-resistant components; With volume control potentiometer, power switch, power input interface, audio input and output ports on board, convenient to use; With orange light LED on the bottom of the tubes.