A distortion-canceling push-pull tube amplifier using inexpensive TV tubes, designed by Pete Millett. For more information, schematics, and circuit boards, please visit Pete Millett’s DIY Audio pages for the Engineer’s Amplifier. Circuit boards for this project are also available via Pete Millett’s eBay store.
Instead of the custom Edcor transformer, this version uses a Hammond power transformer well suited for the Engineer’s Amplifier.
Hammond 372HX (or equivalent)
Primary: 120 V / 240 V, 50/60 Hz
High Voltage Secondary: 275-0-275 V AC @ 200 mA, center-tapped
Heater Supply: 6.3 V AC @ 6 A
Rectifier Supply: 5 V AC @ 3 A
This transformer provides robust headroom, excellent regulation, and long-term reliability, making it a proven choice for vacuum-tube audio amplifiers.
The audio output stage uses Hammond push-pull tube output transformers.
Two × Hammond 1650H Output Transformers
Power Rating: 30 W
Primary Impedance: 8 kΩ (push-pull)
Secondary Impedances: 4 Ω, 8 Ω, and 16 Ω
Wide frequency response suitable for high-quality audio reproduction
These transformers are well known for their solid construction, neutral tonal character, and consistent performance in high-fidelity tube amplifier designs.
All Hammond transformers are wound using high-quality copper magnet wire, designed for optimal electrical performance, durability, and thermal stability.
Hammond transformers utilize high-grade grain-oriented silicon steel laminations, carefully selected to ensure low losses, minimal distortion, and excellent magnetic efficiency.
Precision-engineered bobbins are used to ensure consistent winding geometry, mechanical stability, and long service life.
Power transformer leads: UL-approved insulated lead wire, suitable for high voltage and heater currents
Output transformer leads: Color-coded insulated leads for easy and reliable wiring
All transformers are supplied with steel end bells for chassis mounting using four screws. The end bells feature Hammond’s classic black painted finish, providing a clean, professional appearance suitable for both open and enclosed tube amplifier builds.
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