15W Valve Modulator Amplifier circuit

The output of this modulator consists of two 6AQ5 lamps arranged in a push-pull configuration with a maximum output of 15W. A 6C4 lamp is employed as a reversing lamp. The double-stage ESC83 serves as the pre-amplifier. The potentiometer R1 is utilized for adjusting voice volume, and a crystalline microphone is connected to the amplifier input. The amplified frequency range extends from 50 Hz to 10 kHz, with a 0.7% drop in amplification at these extreme frequencies, measured at 3 dB. The distortion of the amplifier is approximately 8%. The T1 transformer features a primary impedance of 10 kΩ and a transformer ratio of about 1, with the core rated at 15W. The power supply incorporates a 5U4 lamp as a rectifier, with a primary voltage of 220V and a secondary output of 2 x 300V at 150mA, along with 6.3V at 2A and 5V at 2A. The smoothing filter choke is rated at 10H for 15mA. This modulator can facilitate the formation of a transmitter capable of up to 100 Watts, achieving a modulation depth between 90% and 100%.

The described circuit utilizes a push-pull arrangement of two 6AQ5 vacuum tubes, which are known for their efficiency in audio amplification. This configuration effectively cancels out even-order harmonics, reducing distortion and enhancing audio quality. The 6C4 tube acts as a reversing lamp, which is essential for providing the necessary phase inversion in the circuit.

The ESC83 pre-amplifier is a double-stage device that allows for initial signal amplification before further processing. The choice of a crystalline microphone ensures high sensitivity and fidelity in sound pickup, contributing to the overall performance of the audio system. The volume control, implemented through potentiometer R1, allows for user adjustment of the output level, making the system versatile for different audio sources.

The frequency response of the amplifier, spanning from 50 Hz to 10 kHz, accommodates a broad range of audio signals, ensuring that both low and high frequencies are adequately amplified. The noted 0.7% drop in amplification at the extremes suggests that while the amplifier is capable of handling a wide frequency range, there may be slight losses in fidelity at the edges of this spectrum. The distortion level of approximately 8% is acceptable for many audio applications, indicating that the circuit is designed for moderate fidelity rather than high-end audio performance.

The T1 transformer plays a crucial role in impedance matching, with its primary impedance of 10 kΩ ensuring that the amplifier operates efficiently. The transformer ratio close to 1 indicates that there is minimal voltage transformation, which is suitable for maintaining signal integrity. The transformer core rated at 15W confirms its capability to handle the power levels involved without saturation.

The power supply section, utilizing a 5U4 rectifier, is designed to convert AC voltage to DC, providing stable operating conditions for the amplifier circuit. The specified secondary voltages of 300V and lower voltages for heater circuits (6.3V and 5V) are standard for tube amplifiers, ensuring that all components receive appropriate power levels.

The inclusion of a 10H smoothing filter choke enhances the power supply's performance by reducing ripple voltage, which can affect audio quality. With the ability to create a transmitter capable of 100 Watts and a modulation depth of 90% to 100%, this circuit is well-suited for applications requiring robust audio transmission capabilities. Overall, the design reflects a careful balance between performance, efficiency, and usability in audio applications.The output of this modulator consists of two 6AQ5 lamps in a PUSH-PULL arrangement with a maximum output of 15W. 6C4 is used as a reversing lamp. The pre-amplifier role is played by the double-stage ESC83. The potentiometer R1 performs voice volume adjusters and a crystalline microphone is connected to the amplifier input.

The amplified frequency band extends from 50C / S to 10KC / S. At these extreme frequencies amplification drops 0.7% by 3DB.

The deformation of the amplifier is approximately 8%. The T1 transformer has a primary impedance of 10KΩ, and the transformer ratio is about 1. Naturally, the transformer core is estimated at 15W. The power supply uses the 5U4 lamp as a rectifier. The power adapter has a primary 220V and secondary 2 x 300V for 150mA, 6.3V for 2A and 5V for 2A. The smoothing filter choke is 10H for 15mA. It is possible with this modulator to form from the protective grid a transmitter of up to 100 Watts, with a modulation depth of 90% to 100%.