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

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AM/FM Stereo Tuner
high FM frequencies, try moving the tap away from the ground end, but no farther than 1.5 turns
from the ground end (the center of the coil).
6.1.2 Oscillation
If the tuner operates but tends to whistle when a station is tuned in, or very low sensitivity is
evident, it is possible that the unit is oscillating. A reliable indication is a high negative AVC
voltage when no station is tuned in. Oscillation is usually caused by poor connections or
improper lead dress. Resolder any connections about which there may be some doubt. A defective
tube may also cause instability and substitution is the only definitive test. Slight adjustment of the
IF transformers will often stabilize the tuner, especially when it is unaligned.
6.1.3 Hum and Noise
A certain amount of noise is normal when the receiver is tuned between stations. This noise
should disappear or quiet substantially when a station is tuned in, depending on the signal
strength. Failure to quiet properly may indicate improper alignment or a poor antenna installation
if the tuner is receiving distant stations. Oscillation can cause excessive noise in the receiver, as
can a defective tube. In some cases, 60 Hz frequency modulation of the oscillator may result in
hum in the output of the FM tuner.
The antenna lead-in can pick up noise. In the case of the FM tuner, this noise can be reduced
by twisting the lead-in approximately one turn for each two feet of 300
Ω
ribbon cable.
6.1.4 Excessive Drift
A small amount of drift will normally be noticed during warm-up of the tuner, but it will quickly
stabilize. Usually the drift will be noticeable only on weak stations. Continuous drifting is
typically caused by a poor connection or a defective component, most likely a tube. Improper
tuning can also result in drift over time. Under certain conditions, the IF stages can drift but this is
relatively small unless something is wrong with the circuit.
6.1.5 Low Sensitivity
Lack of sensitivity may be traced to improper alignment or to a defective tube. Both should be
checked if optimum performance is to be obtained. Also, the loop antenna (AM) and dipole (FM)
are directional and should be oriented for best overall results.