Figure 8.10 Tube Stereo Demultiplexer. With 6 exceptions there are no component values or numbered designations in this diagram. The input goes through a capacitor to the grid of a triode. The cathode goes through two resistors in series to ground. The junction of the two resistors goes through a resistor to the grid. The plate goes to the bottom of the primary of a transformer. The top of the primary goes to B plus 2. The transformer is labeled 23 to 53 kHz filter. We will come back and pick up the secondary later. Meanwhile the cathode of the triode goes through a capacitor then the primary of a transformer which is labeled 19 kHz. The capacitor forms a 19 kHz series tuned circuit with the inductance of the transformer primary. The secondary is center tapped and the center tap is grounded. One end goes to the anode of a semiconductor diode. The other end goes to the anode of another semiconductor diode. The cathodes of these two diodes are connected together. This forms a frequency doubler so the frequency at the two cathodes is 38 kHz. The diode cathodes go through a capacitor to the grid of a pentode. The cathode of the pentode goes to a tap which is near the bottom of a coil. It is labeled 38 kHz oscillator. The bottom of the coil goes to ground. There is a capacitor in parallel with the coil. The top of the coil goes through a capacitor to the grid. There is a resistor from the grid to ground. The screen grid goes to B plus 1. The screen also goes through a capacitor to ground. The suppressor goes to ground. The plate goes to the bottom of a transformer primary. It is labeled 38 kHz. The top goes to B plus 1. The bottom of the secondary is grounded. The top goes to the bottom of the secondary of the 23 to 53 kHz filter transformer. The top of this secondary connects to a dual diode tube as follows. The top of the filter secondary connects to the plate of diode 1 and the cathode of diode 2. The cathode of diode 1 connects to one end of a 75 k ohm resistor. The other end of this resistor goes through a 0.001 u f capacitor to ground. The plate of diode 2 goes through another 75 k ohm resistor and 0.001 u f capacitor to ground. The triode which was first to be described has its cathode connected to a coil which is labeled 15 kHz low pass filter. The other end of this coil goes through a capacitor to ground. The junction of the coil and capacitor goes through another capacitor to one end each of two 75 k ohm resistors. The other end of one of these resistors goes to the far end of the 75 k ohm resistor that comes from the cathode of diode 1. We will call this point L. The other end of the other of these two resistors goes to the far end of the 75 k ohm resistor that comes from the plate of diode 2. We will call this point R. Point L goes through a resistor to ground and through a capacitor to the left output. Point R goes through another resistor to ground and through another capacitor to the right output. End verbal description.
go back.