Picture tube circuit controls
The following section gives an overview about the Picture Tube Circuit Controls.
Overview of Picture Tube Circuit Controls:
- Manufacturers usually recommend a sufficiently high voltage to the second anode of the picture tube to produce adequate screen brilliancy for normal viewing.
- This voltage is always obtained from the output of the horizontal deflection circuit.
- The dc voltages to the screen grid and focus grid are also taken from the horizontal stage and adjusted to suitable values by resistive potential divider networks.
- This is shown in Fig. 4.8
Figure 4.8 Picture tube circuit and associated controls
- A variable bias control either in the cathode circuit or control grid lead is provided to control the electron density, which in turn controls the brightness on the screen.
- This control, known as the ‘brightness control’, is brought out at the front panel of the receiver to enable the viewer to adjust brightness.
- No focus control is normally provided and instead dc voltage at the focus electrode is carefully set as explained above.
- The contrast control through not strictly a part of the picture tube circuit forms part of cathode or control grid circuit.
- This control is also provided at the front panel of the receiver and its variation enables adjustment of contrast in the reproduced picture.