WhitakerAudio JC Whitaker 20 W Stereo Integrated Audio Amplifier, Manual

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WhitakerAudio
• Harmonic distortion 0.75% or less at 5 W
• Intermodulation distortion 1.5% or less at 5 W
• Phonograph preamplifier included
• Front panel switchable inputs (Phono, Line Input, Front Panel Aux)
• Front Aux input impedance 10 k
Ω
, 0.3 V rms nominal for full power output
• Line input impedance 10 k
Ω
, 1 V rms nominal for full power output
• Separate Bass and Treble tone controls provided
• Conservatively rated components used throughout
• Soft-start power supply to extend component life
• Adjustable output tube bias for optimal performance
• Automatic circuit protection built in, including auto-off feature
• Power requirements: 120 V ac, 60 Hz, 120 W nominal.
• Physical dimensions: 19-in wide by 16-in deep by 7-in high. Note that the depth
specification does not include back panel cables.
• Weight approximately 40 lbs.
The amplifier is built around four main printed wiring boards (PWBs) and four special-
purpose boards, engineered for top performance. Component placement and board traces have
been engineered to minimize hum and noise. The boards feature a unique mounting technique for
the vacuum tubes that keeps heat away from the PWB and minimizes hum in the amplifier. The
PWBs are designed to reduce off-board connections, thereby simplifying layout and providing for
controlled characteristics from one unit to the next. The PWBs include top and bottom solder
masks and top-side silk-screened legends.
The power supply uses a vacuum tube rectifier feeding a choke and followed by a high-
capacity bank of filter capacitors.
The phonograph preamp and tone control circuits utilize discrete transistors. The circuits are
based on classic 1960s designs. This approach intends to maintain the tube-era sound, even for a
solid-state implementation. The benefits of transistors in this design include low noise and small
physical size.
The active circuits of the power amplifier utilize a 6U8A input amplifier and phase splitter.
The power output stage is built around a matched pair of 6973 beam power tubes. Top-quality