WhitakerAudio J C Whitaker 20 W Stereo Audio Amplifier, Manual

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WhitakerAudio
• Noise 70 dB below rated output (unweighted)
• Frequency response ±1 dB 10 Hz to 50 kHz at typical listening level (5 W)
• Harmonic distortion 0.75% or less at 5 W
• Intermodulation distortion 1.5% or less at 5 W
• Power supply for separate preamplifier included
• Line input impedance 100 k
Ω
, 1 V rms nominal for full power output
• 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 three main printed wiring boards (PWBs) and five 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 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 Hammond transformers are used throughout. The transformers are
conservatively rated, providing wide operating margins.
The output circuit utilizes a screen-tap configuration to optimize sonic performance. Generous
power supply filtering ensures a rock-steady reserve for the output stage.
Adjustable bias to the push-pull output tubes provides a wide range of operating points,
allowing users to find a good middle point between top performance and long tube life.