Will the dirty inside of the power amplifier affect the sound quality?

This depends on the specific situation, such as dust, oil pollution, humidity and so on. If there is too much dust, the dust will conduct electricity in wet weather, which will cause the bias resistance of the transistor of the power amplifier to change, the static working point of the transistor will be affected, and distortion will occur. , will seriously burn out the power amplifier tube. You can use a powerful hair dryer to blow it clean. If the oil stain is difficult to remove, it can be washed with cotton swab dipped in neutral detergent and then washed with anhydrous alcohol.