Vacuum Tube Selection
Vacuum tube is one of the earliest electrical signal amplifier components. A cathode electron-emitting portion, a control grid, an acceleration grid, and an anode (screen) lead enclosed in a glass container (generally a glass tube) are welded to the tube base. An electric field is used to inject an electronic modulation signal into the control gate in the vacuum, and different parameter signal data after the signal amplification or feedback oscillation is obtained at the anode. In the early days, it was used in electronic products such as televisions and radio amplifiers. In recent years, it has been gradually replaced by amplifiers and integrated circuits made of semiconductor materials. However, in some high-fidelity audio equipment, vacuum tubes with low noise and high stability are still used as audio power amplifier parts.
When selecting an electronic tube, we should determine the appropriate tube type according to the characteristics and requirements of the specific application circuit firstly. Secondly, it should be ensured that parameters of the selected tube meet the requirements of the application circuit, especially the limit parameters must have sufficient margin.
The visual inspection can be performed by the following methods without using a special test instrument.
- Observe the color of the top of the tube. A normal tube is silver or black color on the top. If the top has become milky white or light black, the tube has leaked or aged.
- Observe if there are the debris in the tube. Gently shake or use your finger to gently bounce glass shell of the tube. Then tilt it upside down to see if there are debris, white oxide, broken mica and other debris. If there is a foreign matter in the electron tube, it means that the tube passes through the centering vibration, and the possibility of short circuit between the internal poles is large.