WhitakerAudio AM/FM Stereo Tuner 2012, Сборка и руководство пользователя

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7 Setup and Alignment
It is tempting to put the AM/FM Stereo Tuner into service upon completion of the previous steps.
However, for best performance, the following tests and adjustments should be conducted.
Users may hear shortly after the tuner is powered on a slight buzzing noise from the chassis
for a few seconds. This is normal. As the tuner warms up, the surge-limiting power thermistor
bypass circuit of VR2 and C36 ramps up the voltage to relay RYL1. During a brief portion of this
ramp, the relay may vibrate slightly; however, within a few seconds the relay will close. The
speed of this action is a function of the ambient temperature.
In the steps that follow, whenever it is necessary to make a connection inside the tuner, switch
the unit off and let all filter capacitors fully discharge. When instructed to switch the receiver on,
allow at least 60 seconds for warm-up and stabilization before taking measurements or making
adjustments.
An aluminum shield plate is provided with the tuner to increase the accuracy of alignment.
For initial adjustments, the shield is not used. After a first-run-through, it is recommended that
touch-up adjustments be made with the shield in place.
7.1 AM Section
6
Figure 7.1 illustrates a conventional AM receiver IF response curve and shows sideband
attenuation at several frequencies. Audio response will be roughly equivalent to one half of the IF
waveform without compensation. A wide-band transformer is used at the input of the IF system,
6. The setup and alignment steps described here and Figures 7.1 and 7.2 are adapted from: Heathkit: “Assembly and Operation of
the Heathkit Broadcast Tuner Model BC-1A,” the Heath Company, Benton Harbor, MI,
Figure 7.1 AM tuner IF bandpass response.
( a ) ( b ) ( c )