A preamplifier input terminal which is connected to the pick up tube by a direct current connection is connected to a control electrode of a transistor , to {HEAD ~ a terminal} of a resistor and, in accordance with the invention, by a diode to a terminal carrying {TAIL ~ a reference voltage} 
A preamplifier input terminal which is connected to the pick up tube by a direct current connection is connected to a control electrode of a transistor , to { HEAD ~ a terminal } of a resistor and , in accordance with the invention , by a diode to a terminal carrying { TAIL ~ a reference voltage }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL