80 Watt Stereo Amplifier AA-40

• alternative name: Heath Company

The Heathkit AA-40 is a vintage high-fidelity vacuum tube stereo power amplifier originally released as a kit in 1962. It is highly regarded by collectors for its "massive iron" transformers and clean, classic analog sound.

Technical Specifications:
The amplifier is designed with a common power supply that provides voltages to both channels, featuring separate input levels and bias adjustments for each. 
Power Output: 40 watts per channel into 8Ω in stereo mode, or 80 watts into 8Ω when switched to mono operation.
Frequency Response: 20Hz to 20kHz.
Total Harmonic Distortion (THD): 1.5%.
Signal to Noise Ratio: 85dB.
Dimensions: 15 inches wide, 11 inches deep, and 7.25 inches high.
Weight: 35.75 lbs (approximately 16.2 kg).

Tube Complement and Internal Components: 
The AA-40 uses a specific "valve complement" to achieve its output power and sound characteristics. 
Output Tubes: 4 x EL34 (two per channel).
Driver/Input Tubes: 2 x 6AN8.
Semiconductors: Includes 4 silicon diodes and 1 selenium diode rectifier for bias voltage.
Rectifier Circuit: Uses a voltage-doubling circuit for the main power supply.

Performance and Maintenance:
Expert reviewers and enthusiasts often compare the AA-40 to having two Heathkit W-7 amplifiers on a single chassis. 
Restoration: Due to its age, many units found today require restoration, including replacing coupling and electrolytic capacitors. Restoration kits are still available from specialist sellers like those on eBay.
Adjustments: The unit includes built-in bias voltage and balancing adjustments, though an external voltmeter is required to set them accurately.
Reliability: According to users on diyAudio, these amplifiers are "keepers" that can rival modern high-end gear when properly reconditioned. 

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Elenco delle radio e altri apparecchi della Heathkit (Brand), Heath Co.; Benton Harbor (MI)