The world of audio amplifiers offers a multitude of designs, each striving to achieve exceptional sound reproduction. The transformer-coupled SET amplifier, like the one depicted in this schematic, represents a classic approach valued for its sonic characteristics and relative simplicity.
This design philosophy prioritizes core functionalities, employing a minimalist approach to achieve a warm, detailed, and engaging listening experience. Let’s delve into the inner workings of this circuit to understand how it accomplishes this feat.
Explanation of Stages:
- Input Stage (V1: 12AX7): The signal from your audio source (e.g., turntable, phone) enters the first triode section of the 12AX7 tube (V1a). This stage amplifies the weak input signal.
- Coupling Capacitor (C1): Blocks DC voltage from the previous stage while allowing the AC audio signal to pass to the next stage.
- Grid Resistor (R1): Sets the input impedance of the first triode section and affects gain.
- Cathode Bypass Capacitor (C2): Improves AC signal fidelity and stability in the first triode section.
- Phase Inverter Stage (V1b): The second triode section of the 12AX7 tube (V1b) inverts the phase of the amplified signal. This is a common technique in single-ended amplifier designs to drive the push-pull output stage.
- Coupling Capacitor (C3): Blocks DC voltage from the previous stage while allowing the AC audio signal to pass to the output stage.
- Output Stage (VT2a & VT2b: 6AQ5): The two 6AQ5 tubes (VT2a and VT2b) are connected in a push-pull configuration, a common design for power amplifier stages in SET amplifiers. This configuration utilizes both the inverted and non-inverted signals from the phase inverter stage to improve efficiency and reduce distortion.
- Output Transformer (Tr1): Matches the impedance of the push-pull output stage to the speakers for efficient power transfer and optimal sound reproduction.
- Power Supply (Not Shown): The schematic doesn’t depict the power supply section, but a complete amplifier would include a power transformer, rectifier tube (likely a 5Y3K), filter capacitors, and voltage regulator circuits to provide the necessary DC voltages for each stage of the amplifier.
Key Points:
- This is a simplified explanation based on the visible components in the schematic. A complete understanding of the amplifier’s operation would require the entire circuit diagram, including the power supply section and component values.
- Transformer-coupled SET amplifiers are known for their warm sonic characteristics and simple design. However, they typically have lower output power compared to other amplifier designs.
Safety Reminder:
Tube amplifiers operate with dangerous voltages. If you’re working with this amplifier circuit, exercise caution and follow proper safety precautions as you would with any high voltage equipment. Consider consulting with a qualified professional if you’re not comfortable working with electronics and high voltage systems.
Bill of Materials (BOM):
Note: Due to the incompleteness of the schematic (missing power supply section) and the absence of specific component values, this BOM provides general component categories:
- Input Stage:
- 1x 12AX7 Tube
- 1x Resistor (value to be determined by design)
- 2x Capacitors (values to be determined by design)
- Phase Inverter Stage:
- (Utilizes components from the 12AX7 tube in the input stage)
- Output Stage:
- 2x 6AQ5 Tubes
- 1x Output Transformer (impedance to match speakers)
- Other Potential Components (power supply not shown in schematic):
- Power Transformer
- Rectifier Tube (e.g., 5Y3K)
- Filter Capacitors
- Voltage Regulator Components (resistors, capacitors, etc.)
- Chassis to house the circuit components
- Hookup Wire for connections within the circuit
- Hardware (screws, nuts, standoffs) for mounting components within the chassis
Additional Notes:
- Building a tube amplifier requires expertise and knowledge to handle high voltages safely. Always refer to a verified and complete schematic diagram for accurate component selection and assembly instructions.
- Consider safety certifications: If you plan to purchase a pre-built amplifier, look for models with safety certifications from reputable organizations.
I hope this introduction, explanation, and bill of materials provide a good starting point
