It’s very important to maintain the stability and accuracy of the operating points of the tube amplifier, especially of the power tube. The screen current changes when the tube gets ageing, or replacing the tube. Break away of the required operating points will influence sound resolution and the stability of the machine. So, please check and adjust the screen current after a long time of use, and it is the same when changing the tube.
Methods of Measurement of the TUBE BIAS VOLTAGE
Use a multi-meter to measure. Adjust the multimeter to volts d.c. 1V range, and the volume of the amplifier the minimum, then insert the anode of the multi-meter pen into the positive hole, and the cathode into the negative hole respectively. The bias voltage should be about 0.9V when the standard input voltage is 230V or 115V.
Adjustment Methods of the Tube Screen Current
When replacing the tube, use a multi-meter to see whether there is a deviation from the screen current. (It should be about 0.9V when the standard supply voltage is 230V or 115V). If you find out a deviation, please use tools to adjust the variable resistance in each DIAS ADJ. hole. The variable resistance increases clockwise, and decreases counter-clockwise. Make sure that the screen current is about 0.9V when the standard supply voltage is 230V or 115V. Measure and adjust it once again when the tube is hot enough.