A bias circuit includes a first transistor, a second transistor, a first resistor and a second resistor. The first end of the first transistor is coupled to a first voltage source. One end of the first resistor is coupled to the second end of the first transistor, and the other end of the first resistor is coupled to the control terminal of the first transistor. The first end of the second transistor is coupled to a second voltage source, and the second end of the second transistor is coupled to the control terminal of the first transistor. One end of the second resistor is coupled to the other end of the first resistor, and the other end of the second resistor is coupled to the control terminal of the second transistor.

Multiple example valve amplifiers are provided. A first example valve amplifier is provided which comprises (i) a valve power amplifier switchable between a high-power mode and a low-power mode and (ii) a loudspeaker simulator circuit, the valve amplifier being configured such that the valve power amplifier drives the loudspeaker simulator circuit in the low-power mode. A second example valve amplifier is provided which comprises a switched-mode power supply, SMPS, system), the SMPS system comprising (i) an SMPS and (ii) circuitry configured to enable an output impedance of the SMPS to be switched between first and second output impedances, the first output impedance being lower than the second output impedance.

Multiple example valve amplifiers are provided. A first example valve amplifier is provided which comprises (i) a valve power amplifier switchable between a high-power mode and a low-power mode and (ii) a loudspeaker simulator circuit, the valve amplifier being configured such that the valve power amplifier drives the loudspeaker simulator circuit in the low-power mode. A second example valve amplifier is provided which comprises a switched-mode power supply, SMPS, system), the SMPS system comprising (i) an SMPS and (ii) circuitry configured to enable an output impedance of the SMPS to be switched between first and second output impedances, the first output impedance being lower than the second output impedance.

A distributed amplification device with p inputs, p outputs, p amplification paths comprises a redundant reservoir of n amplifiers including n-p back-up amplifiers, an input redundancy ring and an output redundancy ring formed by rotary switches, the input and output redundancy rings sharing the same technology. The internal amplification pathways associated with the n-p back-up amplifiers frame in an interlaced manner the internal amplification pathways associated with the p nominal amplifiers and the amplification paths of the routing configurations each pass through at least five rotary switches. The input and output redundancy rings are topologically and geometrically configured and the family of the routing configurations is chosen such that the electrical lengths of all the paths of one and the same routing configuration of the family are equal.

A distributed amplification device with p inputs, p outputs, p amplification paths comprises a redundant reservoir of n amplifiers including n-p back-up amplifiers, an input redundancy ring and an output redundancy ring formed by rotary switches, the input and output redundancy rings sharing the same technology. The internal amplification pathways associated with the n-p back-up amplifiers frame in an interlaced manner the internal amplification pathways associated with the p nominal amplifiers and the amplification paths of the routing configurations each pass through at least five rotary switches. The input and output redundancy rings are topologically and geometrically configured and the family of the routing configurations is chosen such that the electrical lengths of all the paths of one and the same routing configuration of the family are equal.

In an impedance converter using an electron tube as an active element, output impedance can be made sufficiently low, and the number of circuit elements therefor is decreased and a circuit configuration therefor is made simple. Provided is an impedance converter having an electron tube cathode-follower connected. The impedance converter includes a bias diode that provides a bias voltage to a cathode of the electron tube, high resistance elements that provide a voltage of the bias diode to a grid of the electron tube, a load circuit connected to the electron tube, and a complementary emitter output circuit including two transistors, respective bases of which are connected to one end and the other end of the bias diode.

In an impedance converter using an electron tube as an active element, output impedance can be made sufficiently low, and the number of circuit elements therefor is decreased and a circuit configuration therefor is made simple. Provided is an impedance converter having an electron tube cathode-follower connected. The impedance converter includes a bias diode that provides a bias voltage to a cathode of the electron tube, high resistance elements that provide a voltage of the bias diode to a grid of the electron tube, a load circuit connected to the electron tube, and a complementary emitter output circuit including two transistors, respective bases of which are connected to one end and the other end of the bias diode.

In an impedance converter using an electron tube as an active element, output impedance can be made sufficiently low, and the number of circuit elements therefor is decreased and a circuit configuration therefor is made simple. Provided is an impedance converter having an electron tube cathode-follower connected. The impedance converter includes a bias diode that provides a bias voltage to a cathode of the electron tube, high resistance elements that provide a voltage of the bias diode to a grid of the electron tube, a load circuit connected to the electron tube, and a complementary emitter output circuit including two transistors, respective bases of which are connected to one end and the other end of the bias diode.

In an impedance converter using an electron tube as an active element, output impedance can be made sufficiently low, and the number of circuit elements therefor is decreased and a circuit configuration therefor is made simple. Provided is an impedance converter having an electron tube cathode-follower connected. The impedance converter includes a bias diode that provides a bias voltage to a cathode of the electron tube, high resistance elements that provide a voltage of the bias diode to a grid of the electron tube, a load circuit connected to the electron tube, and a complementary emitter output circuit including two transistors, respective bases of which are connected to one end and the other end of the bias diode.

A hi-fi headphone device with two speakers, an integrated pentode vacuum tube, and a battery. The battery is electrically connected to direct and bias circuits, to provide proper voltage to the vacuum tube amplifiers, wherein input signal is amplified and output to buffer circuits and impedance is matched between the tube and output speaker terminals.