A day to be an official AC DC amplifier, fault show insufficient power output significantly, and sound distortion.qbFservice manual download site
qbFservice manual download site
After the examination, the power supply voltage +24V normal. Check and found that the two do they power output performance deterioration on the damage, after replacing two DD 15 tube, test the power output increased, but the sound is still distorted, loud distortion (see Figure 1). Carefully check the normal front, push tubes and other components and replacement signal coupling capacitance and no effect, suspect circuit by changing the offset the static working point, the circuit was part of the adjustment:qbFservice manual download site
qbFservice manual download site
qbFservice manual download site
1. half-tribe voltage 0.5V-0.7V only original power amplifier and the amplifier output tubes using composite using two DD 15 is clearly insufficient static pressure, easily lead to signal distortion. After repeated tests, when under power amplifier bias resistor 820 ω increases to 1.2k when measured power amplifier half-tribe about 1.2V-1.5V bias.qbFservice manual download site
qbFservice manual download site
2. Front-level logging (V1) quiescent current is small, and canceled b,c V1 add-ins 1M ω resistance between electrodes, to biasing resistor voltage divider, bias on 120K resistance 6.8V bias resistor 15K under ground, and V1-emitter resistance plus 100 μg f electrolytic capacitors, upgrade Exchange gain. After the above changes, the power output was greatly improved, significantly improved sound quality.qbFservice manual download site