Transistor Circuit versus Triode Circuit

• Class-A amplifiers using a transistor as the active component in the circuit typically provide an almost distortion-free output. Transistors are readily available and are less expensive than their vacuum tube (triode) counterparts. Some audiophiles, however, prefer triode circuit amplifiers to transistor circuit amplifiers due to the "warm" harmonic sound that triode-based amplifiers produce.
  
  

Constructing a Transistor-based Class-A Amplifier

• To construct a Class-A amplifier you will need the following: one NPN transistor, three resistors, electrical wire, a DC power supply, electrical pliers and a datasheet detailing the transistor pin-outs. To construct the circuit, you will also need either an electronics breadboard, or a soldering iron and solder.
  
  Cut four lengths of wire. Strip the wires of ½-inch of insulation at each end. Using the first wire, connect one of the leads of the first resistor to the positive terminal on the DC power supply. Connect the other lead of the first resistor to the transistor "collector" lead. Connect one end of the second wire to this electrical joint.
  
  Connect one end of the third wire jointly to the transistor "base" lead and one of the leads on the second resistor. Connect one of the leads on the third resistor to the transistor "emitter" lead. Connect the free leads of the second and third resistor together. Connect the fourth wire jointly to both resistors. Connect the free end of the fourth wire to the negative power supply terminal.
  
  In this circuit, the second wire serves as the output lead, while the third wire serves as the input lead.
  
  

Constructing a Triode-based Class-A Amplifier

• The procedure for constructing an amplifier with a triode in place of a transistor is identical. However, the electrical connections on a triode are named differently than those on a transistor.
  
  In a triode-based amplifier, the "grid" lead is analogous to the transistor "base" lead. The "cathode" lead substitutes for the transistor "emitter" lead, and the triode "plate" lead serves the same purpose as the "collector" in a transistor circuit.
  
  A triode also requires a second power supply. This power supply is used to power the filament heater in a triode. The filament heater must be connected to the power supply for the triode to work.