WhitakerAudio AM/FM Stereo Tuner 2012, Assembly & User Manual

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123
AM/FM Stereo Tuner
– If the generator output is low and it is not possible to obtain –4 V of AVC, use the
maximum obtainable voltage. A generator output voltage of approximately 30 mV rms
should produce an AVC voltage of –4 V.
– Adjust the bottom of transformer T4 for maximum indication.
– Switch the tuner off.
– Connect a 10 k
Ω
0.5 W resistor between input IF transformer T3 terminals 3 and 4,
connecting it in a temporary fashion. This can be accomplished by soldering the resistor
temporarily to the available pads marked “Secondary Test Pins.” This will load the
secondary of the transformer to such an extent that the stage becomes impedance-coupled
and will give a single peaked response for alignment purposes. Alignment with a
voltmeter indicating output from a wide-band IF system is impractical, since indications
will be approximately the same over a spread of 19 kHz, making it impossible to find the
proper peak response.
– Connect the signal generator ground lead to the chassis and the output lead through a 0.01
μ
F capacitor to V2 pin #7. Use the TP pad adjacent to the pin.
– Switch the tuner on.
– Adjust the output of the signal generator to produce about –4 V on the AVC bus (10 mV
rms is typical).
– Adjust the top slug of IF transformer T3 for maximum indication on the voltmeter.
– Switch the tuner off.
– Remove the 10 k
Ω
resistor from T3 terminals 3 and 4. Connect the resistor between
terminals 1 and 2 of T3 in a temporary manner. This can most easily be accomplished by
using the R13 position on the PWB. Recall that R13 may be installed after final tests in
order to narrow the reproduced bandwidth of the tuner, if desired. Connection of the 10
k
Ω
resistor will load the primary of the transformer to such an extent that the stage
becomes impedance-coupled and will give a single peaked response for alignment
purposes. The R13 position is denoted by the legend “Primary Test Pins” on the PWB.