ELECTRICAL PARAMETERS OF DIODES

1-13 The silver spot you will sometimes see on the inside surface of the glass envelope of a vacuum tube is normal. It was caused by the "flashing" of a chemical during the manufacture of the tube. Burning the chemical, called the GETTER, helps to produce a better vacuum and eliminates any remaining gases. ELECTRICAL PARAMETERS OF DIODES Thousands of different tubes exist. While many of them are similar and even interchangeable, many have unique characteristics. The differences in materials, dimensions, and other physical characteristics, such as we have just covered, result in differing electrical characteristics. The electrical parameters of a diode, and any tube, are specific. In the process of discussing these parameters, we will state exact values. Voltages will be increased and decreased and the effects measured. Limiting factors and quantities will be explored and defined. The discussion will be based on simplified and experimental circuits. It is important for you to realize that practically all of the parameters, limitations, definitions, abbreviations, and so on that we will cover in these next paragraphs will apply directly to the more complex tubes and circuits you will study later. Diode parameters are the foundation for all that follows. Symbols You have learned to use letters and letter combinations to abbreviate or symbolize electrical quantities. (The letters E, I, and R are examples.) We will continue this practice in referring to tube quantities. You should be aware that other publications may use different abbreviations. Many attempts have been made to standardize such abbreviations, inside the Navy and out. None have succeeded completely. Table 1-1 lists electron-tube symbols used in the remainder of this chapter. The right-hand column shows equivalent symbols that you may find in OTHER texts and courses. SYMBOLS THIS TEXT MEANING OTHER TEXTS E_p PLATE VOLTAGE, D.C. VALUE E_bb PLATE SUPPLY VOLTAGE, D.C. B+ E_c GRID BIAS VOLTAGE, D.C. VALUE E_g E_cc GRID BIAS SUPPLY VOLTAGE, D.C. C- e_b INSTANTANEOUS PLATE VOLTAGE e_c INSTANTANEOUS GRID VOLTAGE e_g A.C. COMPONENT OF GRID VOLTAGE e_p A.C. COMPONENT OF PLATE VOLTAGE (ANODE) I_p D.C. PLATE CURRENT R_p D.C. PLATE RESISTANCE R_g GRID RESISTANCE R_k CATHODE RESISTANCE R_L LOAD RESISTANCE Table 1-1.—Symbols for Tube Parameters Plate Voltage-Plate Current Characteristic You know that a positive voltage on the diode plate allows current to flow in the plate circuit. Each diode, depending on the physical and electrical characteristics designed into the diode, is able to pass an exact amount of current for each specific plate voltage (more voltage, more current-at least to a point).