Upon completion of this chapter, you will be able to:
1. Determine the number and type of individual tubes contained within the signal envelope of a
2. Explain the function and operating principle of the beam power tube and the pentode tube.
3. State the difference between the capabilities of conventional tubes and variable-mu tubes.
4. Describe the construction of uhf tubes, and explain the effects that ultra-high frequencies have
on conventional-tube operation.
5. Explain the operation of gas-filled diodes, thyratrons, and cold-cathode tubes.
6. Explain the operating principles behind cathode-ray tubes, and the manner in which these tubes
present visual display of electronic signals.
INTRODUCTION TO SPECIAL-PURPOSE TUBES
Because of their great versatility, the four basic tube types (diode, triode, tetrode, and pentode)
covered in chapter 1 have been used in the majority of electronic circuits. However, these types of tubes
do have limits, size, frequency, and power handling capabilities.
Special-purpose tubes are designed to operate or perform functions beyond the capabilities of the
basic tube types discussed in chapter 1. The special-purpose tubes covered in this chapter will include
multi-unit, multi-electrode, beam power, power pentode, variable-mu, uhf, cold cathode, thyratrons, and
MULTI-UNIT AND MULTI-ELECTRODE TUBES
One of the probems associated with electron tubes is that they are bulky. The size of an electron tube
circuit can be decreased by enclosing more than one tube within a single envelope, as mentioned in
chapter 1. There is a large variety of tubes that can be combined into this grouping of "specialty tubes"
called MULTI-UNIT tubes. Figure 2-1 illustrates the schematic symbols of a few of the possible
combinations found in multi-unit tubes.