Power tubes with poor thermal stability can cause midpoint voltage shift.
If the midpoint voltage is high, then the protection relay will definitely not close, first check the power supply at the back stage is normal or not, the power tubes at the end of the amplifier, the insurance resistor and so on, if they are all normal, then we have to check the front stage.
Basic information
Audio equipment is by the sound source (music playback equipment, pickup equipment that is the microphone), control equipment (analog or digital mixing consoles), the audio processor (previously used effects, equalizers, limiter, crossover, signal distributor, delay and other peripherals, and now there are integrated with the above functions of the digital system controller).
Power amplifier (amplifier), speaker composition. Audio has a one-piece and layered two categories. In a combination of audio, it's part of the circuit (including phonograph) are in a shell, this structure is generally used for low-grade combination of audio. In the layered combination of audio, according to the different grades of the machine is divided into different layers.
The combination of more layers of audio: a phonograph layer, a CD player layer, a tuner layer, a double card recording and playback seat layer, a tone controller layer, the main power amplifier layer. In the combination of less layered audio, the jukebox, CD player each divided into a layer, the other for a layer. Miniaturization, digitalization, specialization, film and television is the inevitable development trend of home audio.