Elenco AM/FM Radio Kit - Manual (Page 21)

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Figure 17
Figure 18
AC BANDWIDTH
If an oscilloscope is not available, skip the following test and go directly to Section 2.
You may have to change scales on your VOM for the
most accurate reading. Turn the power OFF. The AC
voltage gain of your audio amplifier is equal to the AC output voltage divided by the AC input voltage, or 1/Vin.
The gain should approximately equal the calculated
gain.
Connect the oscilloscope and audio generator to your
circuit as shown in Figure 18.
Set the audio generator for a frequency of 1kHz and
minimum voltage output. Set the oscilloscope to read
0.5 volts per division. Turn on the power and slowly
increase the volume control to a comfortable level.
Increase the amplitude of the audio generator until the
oscilloscope displays 2 volts peak to peak, (Vpp), at
TP19. It may be necessary to adjust the volume
control. Move the oscilloscope probe to the base of
Q10 (TP16) and record the input voltage here:
Vin = _______ Vpp
(at this point, you may want to verify the AC gain).
Move the oscilloscope probe back to TP19 and slowly
increase the frequency from the audio generator until
the waveform on the oscilloscope drops to 0.7 of its
original reading (1.4Vpp or 2.8 divisions). The
frequency of the generator, when the output drops to
0.7 of its original value, is called the high frequency 3
decibel (dB) corner. Record this frequency here:
(f high 3dB) = __________ kHz.
GND
TP17
GND
TP17
Generator
Oscilloscope
(use AC input)
GND
TP17
GND
TP17
Generator