Discrimination of Triode Electrode and Tube Type

Semiconductor triode, also known as transistor, can be said to be the most important device in electronic circuits. Its main function is current amplification and switching. The diode is composed of a PN structure, and the triode is composed of two PN structures, and a common electrode becomes the base of the triode (represented by the letter b). The other two electrodes are the collector (represented by the letter c) and the emitter (represented by the letter e).

There are many types of triodes, and different models have different uses. Most of the triodes are encapsulated in plastic or metal. The appearance of common triodes is that the electrode with an arrow is the emitter, the one with the arrow pointing outward is the NPN type transistor, and the one with the arrow pointing inward is the PNP type. Actually the direction the arrow points is the direction of the current.   

The models of triodes commonly used in electronic production are generally marked on the plastic case, and the appearance is the same, and they are all TO-92 standard packages. In old-fashioned electronic products, 3DG6 (low-frequency low-power silicon tube), 3AX31 (low-frequency low-power germanium tube), etc. can also be seen, and their models are also printed on the metal shell. The transistors produced in our country have a set of naming rules, and electronic engineering technicians and electronic enthusiasts should understand the meaning of the triode symbol.

The first part of the symbol "3" represents the triode.

The second part of the symbol represents the material and construction of the device:

A——PNP type germanium material; B——NPN type germanium material; C——PNP type silicon material; D——NPN type silicon material. The third part of the symbol indicates the function: U——photoelectric tube; K——switch tube; X——low frequency low power tube; G——high frequency low power tube; D——low frequency high power tube; A——high frequency High power tube.

In addition, the 3DJ type is a field effect transistor, and the one headed by BT indicates a special semiconductor component.

2. Discrimination of Triode Electrode and Tube Type

(1) Visual inspection

① Judgment of tube type

Generally, whether the tube type is NPN or PNP should be identified from the model marked on the tube shell. According to ministerial standards, the second digit (letter) of the triode model, A and C represent PNP tubes, and B and D represent NPN tubes, for example:

3AX is PNP type low frequency low power tube 3BX is NPN low frequency low power tube

3CG is PNP high frequency small power tube 3DG is NPN high frequency low power tube

3AD is PNP low frequency high power tube 3DD is NPN low frequency high power tube

3CA is PNP type high frequency high power tube 3DA is NPN type high frequency high power tube

In addition, there are internationally popular 9011~9018 series of high-frequency low-power tubes. Except 9012 and 9015, which are PNP tubes, the rest are NPN tubes.

② Diode Judgment

Commonly used medium and small power transistors have metal round shell and plastic package (half column type) and other shapes. Figure T305 introduces three typical shapes and tube arrangements.