Summary: The circuit is very simple Diodes D1 D4 and D6 D9 are IN4006 The D5 diode is more interesting It is 1 5KE6 8CA This is special diode 1500 WATT PEAK POWER TRANSIENT VOLTAGE SUPPRESSOR Note J3 On PCB it is small gap between GND and signal wire In older telephone equipment special discharge devices are used for surge protection
Image Dimensions: 400 x 437
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