WhitakerAudio J C Whitaker 20 W Stereo Audio Amplifier, Manual

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20 W Stereo Audio Amplifier
• Use only the amount of heat and solder necessary to do the job. Once a PWB is damaged
by excessive heat it is very difficult to repair. Excessive solder flux on the board will tend
to attract dust, which—at high voltages—can lead to arc-over problems.
• Inspect each solder connection to be certain that the mounting pad or via has been filled.
• Mount large components last. These typically include barrier strips and high-voltage
electrolytic capacitors.
All audio cables of length greater than about 6 inches should use shielded cable. Generally
speaking, the shield should be connected to ground at the load end. Grounding both ends of a
shielded cable to the same ground plane is not recommended as it may lead to circulating currents
that will adversely impact the noise floor.
Efficiently making the socket connections to the PWB requires a bit of practice. The
recommended procedure is detailed in Section 5. Be certain to wear protective eye glasses during
this process, and at other steps in PWB assembly.
The chassis is painted and the transformers are shipped painted. To ensure that the case of
each transformer is grounded, a ground lug is attached to each transformer. This is important for
safety reasons. While quite rare, transformer failures can occur. One failure mode can be a
shorting of one of the windings to the transformer case. By grounding the case, such a failure
would open the circuit breaker and prevent dangerous voltages above the chassis in a fault mode.
Because nearly all of the components are mounted on the PWBs, construction of the amplifier
is relatively straightforward. A decorative acrylic shield is supplied and can be used over the tubes
and transformers if desired.