EL  250
Advanced Analog Circuits
Lab #2: Class A Power Amplifier
Andrew Buettner
Objective
To design and construct a class A single transistor power amplifier. Then to take readings from the amplifier concerning it's operation.
Equipment Used
1) Trainer #
2) Oscilloscope #
3) Multimeter #
4) AC function generator #
5) Various components from the EL  250 lab kit
Procedure
A: Circuit Design
1) Assemble the following circuit:
2) Calculate the values of R_{1}, R_{2}, R_{3}, and R_{4} so that the following specifications are satisfied:
i: b = 150
ii: I_{CQ} = 6  12ma
iii: V_{RC} = 4.8V
iv: V_{RE} = 1.8V
v: I_{R1} = I_{R2} = 20I_{BQ}
B: Circuit Construction and Operation
1) Assemble the following circuit:
2) Measure V_{B}, and V_{C}.
3) Apply a 1KHz signal to the input and maximize the input using the oscilloscope as a reference.
4) Measure the voltage at the output, source, and base.
5) Add a 1KW load resistor across the output.
6) Repeat steps 3 and 4.
Data
1) Diagram 1: Schematic 1  Enlarged view
2) Diagram 2: Schematic 2  Enlarged View
3) Table 1: Resistor values for circuit biasing
Resistor: 
R_{1} 
R_{2} 
R_{3} 
R_{4} 

Value: 
9.1KW 
3KW 
220W 
532W 
4) Table 2: DC Voltages at the Base and collector
Point: 
Base 
Collector 
Emitter 

Voltage: 
2.84V 
6.93V 
2.11V 
5) Table 3: AC Voltages (No Load)
Point: 
Base 
Output 
Source 

Oscilloscope: 
.17V 
4.8V 
1.6V 
DMM (RMS): 
147.1mV 
3.675V 
1.023V 
6) Table 4: AC Voltage (1KW Load)
Point: 
Base 
Output 
Source 

Oscilloscope: 
.17V 
3.2V 
1.6V 
DMM (RMS): 
147.1mV 
2.453V 
1.023V 
Answers to Lab Questions
1) Q: What is the theoretical values for the gain and efficiency with this circuit?
A: A_{v} = 196; A_{i} = .053; Efficiency = 100%
2) Q: What are the actual values of gain and efficiency for this circuit?
A: A_{v} = 28; A_{i} = .688; Efficiency = 57.1%
3) Q: Compare the theoretical and actual values.
A:

Theoretical: 
Actual: 
% Error: 

Av: 
196 
28 
85.7% 
Ai: 
0.053 
0.688 
1198% 
Efficiency: 
100% 
57.1% 
42.9% 
Conclusions
From this lab a simple power amplifier can be built to conform to a basic set of operational standards. However, I do not know the source of the exceptionally large amount of error between the theoretical values and the real ones. I did, however, find it interesting that wave form that occurs at the emitter of the transistor. The wave form was identical to that of the base, only slightly smaller.
Attachments
1) Original Lab Handout
2) Original Lab Data
3) Calculations