Elenco Electronics AM-550TK Instruction Manual download pdf (Page 21)

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Figure 16

Amps COM V/Ω

GND

R10

STATIC MEASUREMENTS

With the power OFF, connect the negative lead of your

VOM to any ground and the positive lead to the emitter

of Q3 as shown in Figure 16. Set the VOM to read 9

volts DC and turn ON the power. The voltage at the

emitter of Q3 should be approximately 1 volt. If your

reading is different by more than 0.5 volts, turn off the

power and check your battery of power supply voltage.

Also check components R7, R9, R10 and Q3.

Q3 BIAS

If you do not have an RF generator or oscilloscope, skip the following test and go to Section 4.

DYNAMIC MEASUREMENTS

With the power turned OFF, connect the oscilloscope and

the RF generator to the circuit as shown in Figure 17.

Set

the RF generator at a frequency of 455kHz, no

modulation and minimum amplitude output. Set the

oscilloscope vertical sensitivity at 1 volt/division. The

scope probe must have an input capacitance of less

than 50pF or it will detune transformer T3. Turn the

power ON and slowly increase the amplitude of the RF

signal until you have 4 volts peak to peak on the

oscilloscope. Tune transformer T3 for a maximum

output while readjusting the RF generator amplitude to

keep 4Vpp at the oscilloscope. After T3 is aligned,

move the scope probe tip to the base of Q3 and record

the peak to peak amplitude of the signal here:

Vb=__________Vpp.

Turn the power OFF. The AC gain of the second IF

amplifier at 455kHz is equal to 4/Vb, and should be

greater than 100. If your gain is less than 100, check

components C7, C8, R7, R9 and R10. Also, make sure

that transistor Q3 is properly installed.

AC GAIN

Oscilloscope

Generator

Figure 17

Probe

.02μF

Output

Adjust

GND

R10

GND

R10

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Elenco Electronics AM-550TK Instruction Manual Page 21

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