JP2013140915A - Transformer for amplifier circuit, power amplifier - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a transformer for amplifier circuit which does not require an air gap in a core even if it is used in a single amplifier, and in which the S/N ratio of an amplifier is enhanced by canceling noise deriving from a power supply, or the like, automatically.SOLUTION: A transformer 10 for amplifier circuit receives, as amplification signals, a first amplification signal 102 and a second amplification signal 104 produced by inverting the phase of the first amplification signal. The primary winding 21 consists of a first coil 23 having one terminal connected with a first potential and the other terminal receiving the first amplification signal, and a second coil 24 having one terminal connected with a second potential lower than the first potential and the other terminal receiving the second amplification signal. The inductance of the first coil is equal to that of the second coil, the first and second coils are arranged so as to have the magnetic polarities opposite from each other, and the core does not include an air gap.

Description

  The present invention relates to an amplifier circuit transformer, a power amplifier, and the like.

  A vacuum tube amplifier using a vacuum tube as an amplification element is used as an audio amplifier, for example. As a type of vacuum tube amplifier, for example, there is a single amplifier (A1 amplifier) capable of constructing a power amplifier circuit with a single ball. An output transformer (OPT, hereinafter simply referred to as “transformer”) used in this single amplifier is provided with an air gap for preventing direct current magnetization of a magnetic core.

  In the invention of Patent Document 1 as well, an air gap is provided in the core in order to prevent DC magnetization of the core due to the DC idle current flowing in the primary winding.

JP 2007-295502 A

“MJ Radio and Experiment October 2003 Issue”, Seikodo Shinkosha Co., Ltd., issued October 1, 2003, p87

  However, providing an air gap in the core increases the magnetic resistance. Then, since it becomes difficult for the magnetic flux to pass by the increase in the magnetic resistance, it is necessary to increase the size of the core. For this reason, the single amplifier has disadvantages that the size is increased, the weight is increased, the cost is increased, and the process of cutting the core is increased.

  In the single amplifier, leakage flux and magnetostriction are generated due to the air gap, and the output signal is likely to be distorted. Furthermore, as described in Patent Document 1 in the background art, there is a problem that the output of a general single amplifier for audio use is, for example, about 3 to 10 watts and is easily affected by distortion.

  Therefore, as a measure for reducing distortion and improving the damping factor, a method of applying negative feedback of overalls may be used. However, since it was originally a small output, it was difficult to apply a large negative feedback. In the single amplifier, even if negative feedback is applied, the damping factor (DF) is about one digit (Non-Patent Document 1).

  Here, in order to compensate for the shortcomings of the single amplifier, a push-pull amplifier (AB1 amplifier) using two vacuum tubes may be used. A push-pull amplifier can obtain a large output (for example, 20 W to 100 W). Further, since the two vacuum tubes act so as to cancel each other's distortion, the distortion of the output signal is small (for example, on the order of 0.1 to several percent).

  In the push-pull amplifier (AB1-PP), the currents flowing through the two vacuum tubes are adjusted to be the same, or vacuum tubes (matched pairs) with uniform characteristics are used. Since these currents are in antiphase, the direct current can be canceled in the primary winding of the transformer to prevent direct current magnetization. Therefore, there is no need to provide an air gap in the transformer core unlike a single amplifier, and the size does not increase. Furthermore, since the hum and noise derived from the power source are canceled by the canceling action, the S / N ratio is improved.

  However, in a push-pull amplifier, it is generally necessary to balance the DC of two vacuum tubes even when a matched pair tube is used. Therefore, a push-pull amplifier needs a DC balance circuit. Furthermore, it is necessary to input AC signals having a phase difference of 180 degrees to each of the two vacuum tubes. Then, a phase inversion circuit is also required, and the circuit scale becomes large. And since two vacuum tubes are used, power consumption is also large. A cross-shunt push-pull method (CSPP) that can lower the output impedance than a general AB1-PP amplifier has been devised. However, even if negative feedback is applied, the damping factor remains at about 10-18.

  Furthermore, with conventional vacuum tube amplifiers, the basic performance and characteristics that amplifiers should have in both A1 single amplifiers and AB1 push-pull amplifiers, such as frequency characteristics, distortion, S / N, and damping factors, have a sense of blockage. There was no significant performance or property improvement over the decade.

The present invention has been made in view of such problems. According to some aspects of the present invention, there is no need to provide an air gap in the core even when used in a single amplifier, and noise derived from a power source or the like is automatically canceled to improve the S / N ratio of the amplifier. An amplifier circuit transformer is provided.

(1) The present invention is an amplifying circuit transformer that includes a primary winding and a secondary winding wound around a core and receives an amplification signal of an amplification circuit by the primary winding, , Receiving a first amplified signal and a second amplified signal obtained by inverting the phase of the first amplified signal, the primary winding having one terminal connected to the first potential and the other A first coil for receiving the first amplified signal, a first terminal connected to a second potential lower than the first potential, and a second terminal for receiving the second amplified signal. The first coil and the second coil have the same inductance, and the first coil and the second coil have opposite magnetic polarities. And the core does not include an air gap. .

(2) In this amplifier circuit transformer, the first coil and the second coil may be bifilar wound.

  In these inventions, the primary winding is constituted by the first coil and the second coil among the primary winding and the secondary winding wound around the core of the amplifier circuit transformer. At this time, the inductance of the first coil and the inductance of the second coil are the same, and the magnetic polarities are opposite to each other (the phases are opposite).

  The same current flows in series from the first coil to the second coil via the amplifier element of the amplifier circuit. Here, since the magnetic polarities of the first coil and the second coil are opposite to each other, no DC magnetization is generated in the core. Therefore, it is not necessary to provide an air gap in the core of the amplifier circuit transformer. Here, the magnetic polarity means a magnetic polarity with respect to a direct current.

  Here, the first coil and the second coil are connected as follows. First, one terminal of the first coil is connected to the first potential, and the other terminal receives the first amplified signal. The first potential is a fixed potential. For example, when the amplification element of the amplifier circuit is a vacuum tube, the first potential may be a plate supply potential determined by the specification of the vacuum tube. The first amplified signal is an AC output signal from the amplifier circuit.

  The second coil has one terminal connected to the second potential and receives the second amplified signal at the other terminal. The second potential is a fixed potential different from the first potential. For example, the second potential may be a ground potential. The second amplified signal is an AC output signal from the amplifier circuit and is a signal obtained by inverting the phase of the first amplified signal. The amplifier circuit generates a second amplified signal whose phase is inverted from that of the first amplified signal based on an input signal.

  At this time, as described above, the direct current is supplied from the first coil connected to the first potential (for example, plate supply potential) through the amplification element of the amplification circuit to the second potential (for example, ground potential). ) To the second coil connected to). The first coil and the second coil have opposite winding directions and opposite magnetic polarities (reverse polarity). Therefore, the direct current does not cause direct current magnetization in the core of the amplifier circuit transformer.

  On the other hand, the first amplified signal and the second amplified signal that are AC signals output from the amplifier circuit are different from the DC current. Since the first amplified signal and the second amplified signal having the opposite phases are supplied to the first coil and the second coil having the opposite magnetic polarities, respectively, the AC magnetic Are in phase.

  In the present invention, the inside of the primary winding is composed of the first coil and the second coil, and the magnetic cores are in phase with each other and strengthen each other, and the DC currents cancel each other in the opposite phase. An amplifier circuit transformer that prevents direct current magnetization is realized.

  In order to make the inductance of the first coil and the inductance of the second coil coincide with each other, the first coil and the second coil may be generated by bifilar winding. Bifilar winding is a method of winding two wires in close contact in parallel. By performing bifilar winding, the degree of coupling between the windings is also increased, and the so-called total conductance (M) can be further increased.

  In addition, since the first coil and the second coil are connected in reverse phase with respect to the direct current, even if there is an alternating current component derived from the power source (for example, a component that generates noise such as ripple or hum), the coil is a coil. On the other hand, since it flows as an in-phase input current, it is automatically canceled and not output to the secondary side. In other words, the S / N ratio of the amplifier can be improved without providing a special circuit such as a large ripple filter made of a large choke coil and a large-capacity electrolytic capacitor, which are said to be essential for an A1 single amplifier. Can do. Furthermore, the power supply ripple filter may have a simple circuit configuration.

  For the AC signal, the first amplified signal and the second amplified signal are synthesized in phase between the two coils in the transformer. That is, twice the combined magnetic flux is generated in the core of the amplifier circuit transformer. This means that a double output can be taken from the plate electrode and cathode electrode of one vacuum tube based on the same plate current. Therefore, a power amplifier (power amplifier) using the amplifier circuit transformer of the present invention can achieve very high power efficiency.

(3) A power amplifier, including the amplifier circuit transformer described above and the amplifier circuit in which the amplifier element is a vacuum tube.

(4) In this power amplifier, the amplifier circuit may use a horizontal deflection output tube as the vacuum tube.

(5) In this power amplifier, the output from the plate side of the vacuum tube may be the first amplified signal, and the output from the cathode side of the vacuum tube may be the second amplified signal.

  According to these inventions, the amplification element of the amplification circuit is a vacuum tube, and the first amplification signal and the second amplification signal obtained by inverting the phase of the first amplification signal are respectively transmitted from the plate electrode and the cathode electrode. These signals can be used. Due to the characteristics of the vacuum tube, the signals from these electrodes have a phase difference of 180 degrees from each other. Therefore, for example, a signal having an opposite phase can be accurately obtained without specially providing a phase inversion circuit.

  For example, the output from the plate side of the vacuum tube may be the first amplified signal, and the output from the cathode side of the vacuum tube may be the second amplified signal. Conversely, the output from the plate side of the vacuum tube may be the second amplified signal, and the output from the cathode side of the vacuum tube may be the first amplified signal.

  In these inventions, power amplification is performed by current drive. Therefore, the vacuum tube may be a horizontal deflection output tube (Sweep tube) capable of flowing a large current. The horizontal deflection output tube is used for, for example, a TV cathode ray tube or the like for sweeping from a small current to a large current, and has high resistance against overload. Further, the vacuum tube may be a transmission tube capable of flowing a large current.

  A power amplifier including an amplifying circuit using a horizontal deflection output tube and the amplifying circuit transformer has not only an effect of improving the S / N ratio but also a long-term reliability. .

(6) A power amplifier including the amplifier circuit transformer described above and the amplifier circuit in which an amplifier element is a bipolar transistor.

  According to the present invention, by using a bipolar transistor having a large amplification factor as an amplification element of an amplifier circuit, effects such as reduction in output impedance of the amplifier and increase in S / N ratio are improved. Further, since the size can be reduced, the application range is expanded. For example, it can be used for various purposes such as an output device for communication in addition to an audio device. In addition, as long as it is a semiconductor element with a high amplification factor, it is possible to use not only a bipolar transistor but also a power type field effect transistor (MOS-FET).

(7) Two first transformers and second transformers which are the transformers for the amplifier circuit described above, two first amplifier circuits which are the amplifier circuits and the amplification element is a vacuum tube, and second transformers In a power amplifier including an amplifier circuit and a phase inverting circuit that generates signals whose phases are inverted with each other, the secondary winding of the first transformer and the secondary winding of the second transformer are shared, The phase inverting circuit generates a first signal and a second signal obtained by inverting the phase of the first signal based on an input signal, and the first transformer generates the first signal. The output from the plate side of the vacuum tube of the first amplifier circuit is a first amplification signal, and the output from the cathode side of the vacuum tube of the second amplifier circuit is a second amplification. And the second transformer is a front The second signal is the grid signal of the vacuum tube, the output from the plate side of the vacuum tube of the second amplifier circuit is the first amplified signal, and the output from the cathode side of the vacuum tube of the first amplifier circuit Is the second amplified signal, and the magnetic polarity of the first coil and the second coil of the second transformer is the same as that of the first coil and the second coil of the first transformer. It is arranged to be opposite to the target polarity.

(8) Two first transformers and second transformers that are amplifier circuit transformers as described above, two first amplifier circuits that are amplifier circuits, and the amplification elements are vacuum tubes, and second transformers In a power amplifier including an amplifier circuit, the secondary winding of the first transformer and the secondary winding of the second transformer are shared, and one input signal is supplied to the vacuum tube of the first amplifier circuit. The grid signal and the grid signal of the vacuum tube of the second amplifier circuit are in-phase signals, and the first transformer outputs the output from the plate side of the vacuum tube of the first amplifier circuit to the first An output from the cathode side of the vacuum tube of the second amplification circuit is set as a second amplification signal, and the second transformer outputs an output from the plate side of the vacuum tube of the second amplification circuit. First amplified signal And, the output from the cathode side of the vacuum tube of the first amplifying circuit and the second amplified signal.

  According to these inventions, it is possible to form a push-pull circuit by combining two circuits (basic circuits) constituting the amplifier circuit transformer, and to generate a power amplifier with improved characteristics such as frequency response. it can.

  For example, a circuit configuration including a phase inversion circuit (hereinafter referred to as a phase inversion input type push-pull amplifier or D-CSA1-PP) is possible. Push-pull operations can be performed by reversing the magnetic polarities of the inductances on the output side of the two basic circuits, respectively, by inputting the signals whose phases are inverted from each other, which are output from the phase inverting circuit, to the two vacuum tubes.

  The power amplifier having such a configuration exhibits excellent frequency characteristics over a wide band from, for example, a low frequency of less than 20 Hz to around 150 kHz. Furthermore, the effect of improving the distortion rate is increased. Moreover, even if the vacuum tube of one basic circuit stops functioning due to a failure or the like, the function as a power amplifier can be continued. As a simple example, the output signal continues to be output even if the vacuum tube (tube) on one side is pulled out during operation. Similarly, normal operation continues even if the plate current of the vacuum tube on one side suddenly drops and current imbalance occurs. In the conventional power amplifier, when an unbalanced current flows, DC magnetization advances, resulting in a fatal failure that causes an increase in distortion and no output.

  Also, in-phase signals (grid signals) can be input to the two vacuum tubes, and the push-pull operation can be performed by reversing the AC magnetic polarities of the inductances on the output side of the two basic circuits. At this time, the output from the plate side of one vacuum tube is input to the first coil, and the output from the cathode side of another vacuum tube is input to the second coil that forms a pair. The secondary windings of the two basic circuits are shared.

  In a power amplifier having such a configuration (hereinafter referred to as an in-phase input type push-pull amplifier or E-CSA1-PP), a high frequency band is obtained by a coupling action due to the capacitance between coils constituting each primary winding. Shows excellent frequency characteristics. Further, even if one of the vacuum tubes stops functioning due to a failure or the like, the function as a power amplifier can be continued.

  In this way, a power amplifier configured by combining basic circuits can improve characteristics such as frequency response, and even if one of the vacuum tubes fails or breaks, The function as an amplifier can be continued. The operation at the time of failure is the same as the recovery operation of the phase inversion input type push-pull amplifier.

  The power amplifier having such a configuration operates normally even if a matched pair tube is not particularly used for the two vacuum tubes. As described in the operation of the basic circuit, the operation of one vacuum tube has a DC canceling action in the primary winding of the transformer, so that there is no need for DC balance and the circuit is simplified.

  The power amplifier can also be configured by combining N basic circuits having a common secondary winding, not limited to a combination of two basic circuits.

(9) In this transformer for an amplifier circuit, the primary winding and the secondary winding may be coated with polyimide coating in addition to polyester insulation as an insulating coating.

  According to the present invention, since the dielectric strength is high and the mechanical strength is strong, the layer short circuit does not occur unlike the conventional case. Further, when this wire is used for bifilar winding or multilayer lap winding, these insulating materials form excellent capacitors with little dielectric loss between the wires. Therefore, the high frequency reproduction limit is extended in audio applications, contributing to improvement of characteristics such as distortion.

The figure which shows the circuit (basic circuit) of the transformer for amplifier circuits which the power amplifier of 1st Embodiment contains. The figure which shows the power amplifier which makes an amplification element a vacuum tube (triode tube). FIG. 3A to FIG. 3B are diagrams showing a relationship between a coil terminal and a magnetic polarity. The figure which shows the structural example in case an amplification element is used as a pentode. The figure of the circuit (1st application circuit) which combined the basic circuit which the power amplifier of 2nd Embodiment contains. FIG. 6A to FIG. 6D are diagrams showing fault tolerance in the first application circuit. The figure of the circuit (2nd application circuit) which combined the basic circuit which the power amplifier of 2nd Embodiment contains. FIGS. 8A to 8D are diagrams showing fault tolerance in the second application circuit. FIG. 9A to FIG. 9B are diagrams showing a third embodiment. The figure which shows the power amplifier which uses an amplification element as a bipolar transistor.

1. First Embodiment A first embodiment of the present invention will be described with reference to FIGS.

1.1. Basic Circuit of Amplifier Transformer FIG. 1 shows a basic circuit of an amplifier circuit transformer 10 included in the power amplifier of this embodiment. The amplifier circuit transformer 10 includes a primary winding 21 and a secondary winding 22 wound around a core. The amplifier circuit transformer 10 transmits AC power on the primary winding 21 side (primary side) to the secondary winding 22 side (secondary side) using electromagnetic induction. The primary winding 21 receives a first amplified signal 102 from an amplifier circuit (not shown) and a second amplified signal 104 obtained by inverting the phase of the first amplified signal 102.

The primary winding 21 includes two parts, a first coil 23 and a second coil 24. The first coil 23 receives the first amplified signal 102 at one terminal and fixes the other terminal at the first potential. The second coil 24 receives the second amplified signal 104 at one terminal, and fixes the other terminal to the second potential. In the present embodiment, the first potential is a fixed potential V ₀ and the second potential is a ground potential. The fixed potential V ₀ may be a potential determined by the amplification element of the connected amplification circuit.

  A current corresponding to the electric power transmitted by electromagnetic induction flows through the secondary winding 22. Then, the flowing current is taken out from the output unit 40. In the present embodiment, it is assumed that the current output from the output unit 40 is supplied to, for example, a speaker (not shown) that is a load.

  Note that the first potential is higher than the second potential. Further, the symbols “+” and “−” in FIG. 1 represent the magnetic polarity with respect to the direct current in the first coil 23 and the second coil 24, and details will be described later.

1.2. Configuration of Power Amplifier FIG. 2 is a diagram showing a power amplifier 1 of this embodiment in which an amplifying element is a vacuum tube (triode tube). The amplifier circuit transformer 10 and the amplifier circuit 30 are connected to each other. In FIG. 2, at least a part of the power amplifier 1 is shown, and other elements may be included. Here, the power amplifier 1 of the present embodiment is particularly used as an audio power amplifier, but the application is not limited to audio. The same elements as those in FIG. 1 are denoted by the same reference numerals, and description thereof is omitted.

  The amplifier circuit 30 of the present embodiment uses a vacuum tube 34 as an amplifier element. In addition to the vacuum tube 34, the amplifier circuit 30 may include an input resistor 32, for example, or may include a cathode resistor (not shown) for applying a bias voltage.

  The input signal 100 is an AC signal, and gives the grid voltage of the vacuum tube 34 via the input resistor 32. The first amplified signal 102 received by the first coil 23 is output from the plate side of the vacuum tube 34. On the other hand, the second amplified signal 104 received by the second coil 24 is output from the cathode side of the vacuum tube 34.

  At this time, the signal phase difference between the plate electrode and the cathode electrode in the vacuum tube is always 180 degrees. That is, the first amplified signal 102 and the second amplified signal 104 are signals having opposite phases.

1.3. Operation of the present embodiment 1.3.1. DC component Here, the DC current in the circuit of FIG. 2 will be described. In the present embodiment, a first potential (V ₀ ) that is a plate supply voltage of the vacuum tube 34 is supplied from the B power source. The direct current flows from the B power source, which is the first potential, through the first coil 23, from the plate of the vacuum tube 34 to the cathode, and then to the grounded second coil 24.

  Here, a direct current and its magnetic polarity will be described with reference to FIG. FIG. 3A shows the physical positional relationship between the first coil 23 and the second coil 24. For example, such a physical positional relationship can be realized by bifilar winding the first coil 23 and the second coil 24.

  The first coil 23 and the second coil 24 in FIG. 3A are the same as those in FIG. 2, and the signs of + and − are the same as those in FIG. The terminal side into which the DC current flows is +, and the terminal side from which the DC current flows out is-.

In the first coil 23, the plate current I _dcp flows from the _positive terminal to the _negative terminal. On the other hand, the cathode current I _dck flows through the second coil 24 from the _positive terminal to the _negative terminal. In the vacuum tube 34 (see FIG. 2), since the current flowing into the plate flows out from the cathode, I _dcp and I _dck have the same value.

  Since direct current of the same magnitude flows in opposite directions, the magnetic polarities of the first coil 23 and the second coil 24 are opposite (reverse phase). For this reason, since the magnetic fields cancel each other, no DC magnetization is generated in the core.

  Therefore, the core of the amplifier circuit transformer 10 (see FIG. 2) included in the power amplifier according to the present embodiment does not need to be provided with an air gap that is conventionally required for a single amplifier. The air gap increases the magnetic resistance and makes it difficult for the magnetic flux to pass. In order to compensate for this, the conventional transformer for an amplifier circuit has to have a large core. In the air gap portion, a large magnetostriction is generated, and the output signal is distorted. In the core of the amplifier circuit transformer of this embodiment, since there is no air gap, the size can be reduced, and an output signal can be obtained without any distortion caused by the air gap.

Further, for example, even when there is some ripple in the B power source (V _{0 in} FIG. 2), the magnetic polarities of the first coil 23 and the second coil 24 are opposite to each other. Components (ripple, hum, noise, etc.) can be canceled. For this reason, the influence of these noise components does not have to be given to the secondary side.

  As a result, it is possible to improve the signal-to-noise ratio (S / N ratio) of the amplifier including the circuit of FIG. For example, the generation of hum or the like from a speaker connected to the output unit 40 can be suppressed.

  Here, in order to cancel DC magnetization accurately, it is necessary to prevent a difference in inductance between the first coil 23 and the second coil 24. Therefore, it is preferable to generate the first coil 23 and the second coil 24 constituting the primary winding by bifilar winding. By performing bifilar winding, the inductances of both coils are made equal, and both coils are magnetically coupled tightly, thereby making it possible to cancel DC magnetization accurately in the primary winding.

  However, it has been pointed out as a problem that bifilar winding can cause a layer short (interlayer short) at the manufacturing stage or after shipment. In particular, when applied to an audio vacuum tube amplifier, there is a problem that the product life is not so long.

  A conventional transformer wire has a characteristic that the insulation jacket is thin and easily damaged mechanically, and the pressure resistance is low. In the present invention, as a wire used for an amplifier circuit transformer in the experiment, a TEX-E product manufactured by Furukawa Electric and a similar product were used, and good results were obtained. This product is a wire material developed for power supply devices and digital devices, and is a highly safe and reliable wire material that meets UL safety standards and has a sufficiently high withstand voltage between wires.

  In addition to the double layer insulation of the polyester film, the third layer is coated with a polyimide coating. Therefore, since the dielectric strength is high and the mechanical strength is strong, the layer short circuit does not occur unlike the conventional case. Further, when this wire is used for bifilar winding or multilayer lap winding, these insulating materials form excellent capacitors with little dielectric loss between the wires. Therefore, in audio applications, the high-frequency reproduction limit is extended, contributing to improvement of characteristics such as distortion (experimental reports on characteristic improvement will be described later).

1.3.2. Here, the AC component will be described with reference to FIGS. 2 and 3B. In the present embodiment, based on one input signal 100, a first amplified signal 102 and a second amplified signal 104 whose phases are opposite to each other are generated. Then, the first amplified signal 102 and the second amplified signal 104 are supplied to the first coil 23 and the second coil 24, respectively.

  In the vacuum tube 34 of FIG. 2, the AC component of the second amplified signal 104 which is an output signal on the cathode side is a signal in phase with the input signal 100 to the grid. On the other hand, the first amplified signal 102 flows into the plate side, but has a phase difference of 180 degrees with respect to the input signal 100.

Therefore, as shown in FIG. 3B, the output current I _ack, which is the AC component of the second amplified signal 104, is + I _ack, where the cathode current I _dck flow direction in FIG. Can be represented. On the other hand, the output current I _acp that is the AC component of the first amplified signal 102 can be represented by −I _acp, where the plate current I _dcp flows in FIG.

  That is, in the primary winding, the first coil 23 and the second coil 24 perform AC magnetic phase in-phase synthesis. In FIG. 3B, the direction of the magnetic polarity (magnetic polarity in the active state) with respect to the AC signal of the first coil 23 and the second coil 24 is indicated by “●”. At this time, a double combined magnetic flux is generated for the AC component by in-phase synthesis. This means that a double output can be taken out from one vacuum tube 34 with the same plate current.

  For example, the output efficiency (anode efficiency, ratio of output power to input power) of a conventional A1 single amplifier is said to be about 25%. In the present invention, according to experiments, an output (Po) of 9.5 W is obtained with respect to an input power (Pin) of 23 W to the plate, and a high power efficiency of about 40 to 45% can be obtained. In addition, a large current feedback is applied to the cathode output and the cathode side winding (24) due to the in-phase synthesis, a characteristic improvement effect can be expected, and a high damping factor (DF) is achieved by reducing the output impedance of the entire power amplifier circuit. Similarly, there is an effect of improving the distortion rate as well (details of the overall performance of the characteristic improvement will be described later).

1.4. Here, although the triode is used as the vacuum tube 34 in FIG. 2, the type of the vacuum tube 34 used in the power amplifier of the present embodiment is not limited to the triode. For example, the amplifier circuit 30A of FIG. 4 may be applied instead of the amplifier circuit 30 of FIG. In FIG. 4, the same elements as those in FIGS.

The amplifying circuit 30A uses a pentode as the amplifying element 34A. When a pentode is used, a positive potential (V _{1 in} FIG. 4) needs to be applied to the second grid (screen grid), so that a power source different from that in the circuit of FIG. 2 is required. A beam quadrupole tube may be used as the amplifying element.

  However, the amount of current feedback generated on the cathode side of the vacuum tube depends on the voltage amplification degree (μ) of the vacuum tube used. The larger the value of voltage amplification (μ), the larger the current feedback amount. As the amount of current feedback increases, the output impedance decreases in inverse proportion. Further, improvement effects such as improvement of distortion and improvement of frequency characteristics occur. The degree of improvement is generally expressed by 1 / μ (reciprocal of voltage amplification).

  The voltage amplification degree (μ) of the vacuum tube is higher in the multipolar tube (for example, pentode, beam quadrupole, etc.) than in the triode, so the above-described damping factor, distortion, etc. can be obtained by using the multipole tube. Greater improvements can be made. In the example of a circuit diagram using a vacuum tube described later, a multipolar tube can be used instead of the triode. Even in a multipolar tube, if a vacuum tube having a large internal resistance (rp) is used, a larger damping factor can be obtained. On the other hand, since the damping factor can be increased by using a triode having a low internal resistance in the conventional vacuum tube amplifier, the triode has been used favorably (the value is about 3 to 8). Therefore, the proposed technique and the conventional technique are in the opposite relationship.

1.5. Other features 1.5.1. About Damping Factor The power amplifier of this embodiment has a voltage amplification factor (gain) of 1 (unity gain). This is because the inductance (impedance) of the vacuum tube load is the same on the plate side and the cathode side. For example, in a circuit having impedance on the plate (P) side and the cathode (K) side, the voltage amplification degree G can be simply set as follows using the impedances Z (P) and Z (K) on the respective sides. It can be calculated by equation (1).

  For example, in the PK division phase inverting circuit (see FIG. 9A), the same resistance value (Z (P) = Z (K)) is inserted on the P side and the K side to set the voltage amplification degree G to 1. Invert the phase without changing the amplitude.

  The power amplifier according to the present embodiment needs to be operated as a current amplifier in order to perform power amplification, unlike the method in which the output is extracted by voltage change that has been conventionally performed because the voltage amplification degree (G) is 1. There is. In order to operate as a current amplifier, it is necessary to inject a certain amount of electromagnetic energy into the transformer. Therefore, it is necessary to flow a large current from the vacuum tube to the primary winding of the transformer in advance. However, since the vacuum tube is not a current amplifying element, the power amplifier of this embodiment takes out the current output instead of the voltage output by performing in-phase magnetic synthesis in the primary winding of the output transformer (OPT).

  Here, the power amplifier of the present embodiment includes the amplifying circuit transformer. The primary winding of the transformer includes a first coil and a second coil generated by bifilar winding. At this time, the first coil and the second coil are electromagnetically and electrostatically tightly coupled. The output signal (second amplified signal) from the cathode (K) side can apply a large amount of current feedback to the K side winding (second coil), so that distortion is reduced and the output is reduced. Impedance can be greatly reduced. Furthermore, since both coils are closely coupled electromagnetically and electrostatically, the signal current (plate current ip) in the first coil is equivalent to the K-side current (cathode current ik), and the output impedance is comprehensively determined. Reduction effect and distortion improvement are performed.

  As described above, the current feedback amount depends on the voltage amplification degree (μ) of the vacuum tube being used, and the current feedback amount increases as the value increases. Current feedback mainly lowers the output impedance and further improves distortion and frequency characteristics. The degree of improvement is expressed by the reciprocal of the amplification degree (1 / μ). Therefore, in this embodiment, the triode tube has been conventionally advantageous in terms of sound quality, but it is possible to further improve distortion and frequency characteristics by using a multipole tube with a high voltage amplification degree (μ) instead. become.

Here, the power amplifier according to the present embodiment can significantly improve the damping factor (DF) by significantly reducing the output impedance (Z _O ) due to a large amount of current feedback. For example, in audio applications, the larger the damping factor, the better the driving and braking performance of the speaker, so that reproduction close to the original sound is possible, and sound quality and audibility are improved.

The damping factor DF is obtained by dividing the load impedance (Z ₁ ) by the output impedance (Z _O ) of the power amplifier. The load impedance (Z ₁ ) is, for example, the impedance of the speaker to be used (generally 8Ω). The damping factor DF can be calculated by the following equation (2).

  The power amplifier of this embodiment is an A1 amplifier from the operating point. However, the operating point may be shifted to a position where a larger current can flow. Then, the operating point may be set at a position where the plate current of the multipolar tube does not change suddenly in the anode characteristic diagram of the vacuum tube, generally called a knee (knee). The plate current increases and decreases in proportion to both half-waves of the input signal, and uniform current changes appear above and below the operating point. That is, the input signal and the output signal always appear in a state of 100% as a current change in proportion. The method of placing the operating point in knee is the same for both the basic circuit and the two push-pull circuits. This is largely different from the operation method in which the conventional AB1-push-pull amplifier is operated with a deep bias just before the cut-off in the push-pull circuit and the vacuum tube is conducted only for every half wave of the input signal. is there.

  Placing the operating point at knee enables magnetically highly efficient coupling in the primary winding of the transformer by constantly flowing a signal current on the P side and the K side. Further, since the vacuum tube is always on, current feedback is applied almost completely in the output circuit, and the output impedance is significantly reduced due to large current feedback. Therefore, the damping factor can be improved. In a certain experiment, a damping factor of 50 or more could be easily obtained with the power amplifier of this embodiment.

  Here, the transformer of the conventional A1 amplifier requires an air gap as a measure for preventing DC magnetization, but the output signal contains a lot of distortion due to the adverse effect. On the other hand, the transformer of the power amplifier of the present invention uses a transformer that does not have a source of magnetostriction derived from an air gap that uses a toroidal core in addition to a core material such as a cut core or an EI core and eliminates an air gap. May be. The toroidal core has negligible distortion in the magnetic circuit. Therefore, an output signal with less distortion can be obtained.

1.5.2. About Impedance Matching The power amplifier of this embodiment is a vacuum tube amplifier, and the amplified power signal must be efficiently transmitted to the secondary side as a role of its transformer. Therefore, the connection of the primary impedance (optimum load) of the transformer corresponding to the internal resistance of the vacuum tube is required. When the optimum condition is removed, inconveniences such as a decrease in output and an increase in distortion increase. The impedance matching is adjusted by the primary / secondary winding ratio.

  In the power amplifier transformer, energy is exchanged, but it is necessary to inject a sufficient amount of energy to accurately transmit information. This energy is said to be proportional to the square of the current (I) flowing through the wound inductance (L). Specifically, the energy E can be expressed as in Equation (3).

  Therefore, in the power amplifier of this embodiment, a large idling current is allowed to flow through a small inductance, thereby enabling power signal transmission that includes a large amount of information and has excellent rise characteristics. Specifically, a general A1 single amplifier supplies a load inductance of about 10 mA to about 50 mA to 80 mA, whereas in the present embodiment, a primary inductance having a small value such as 300 mH is used. The idling current is set to a large value such as 400 mA. The fact that the inductance may be small is that the direct current resistance (Rdc) of the coil can be reduced, so that heat generation can be reduced and loss can be reduced, and output impedance is also reduced. Therefore, it becomes possible to obtain a high damping factor (DF).

  When a large current flows, a large output current change can be obtained with respect to an input signal change, which means use in a region with good linearity in the normal magnetic curve (BH curve) of the core of the transformer, which is a magnetic material. For this reason, distortion in the output signal can be reduced.

  For example, in audio applications, when a conventional A1 amplifier or the like is used to reduce the volume and listen at a small output, a curved portion near the origin of the BH curve is used. For this reason, there has been a problem that distortion appears prominently and sound quality deteriorates. In the power amplifier according to the present embodiment, such a problem in the conventional audio A1 amplifier can be solved.

  In the power amplifier of this embodiment, the plate current flows most during idling. As the input signal is input, the current decreases and the plate current behavior is opposite to that of the conventional A1 single amplifier. This means that it is sufficient to ensure the power supply capacity in the initial state, and the plate current of the output tube decreases as the output increases.

1.5.3. About the theoretical formula of a damping factor According to some experiments, a damping factor (DF) of 50 or more can be easily realized by using the power amplifier of this embodiment. Since DF is obtained by Expression (2), it becomes higher as the output impedance Z _O is lower.

  Here, the internal resistance rp of the vacuum tube is expressed by Expression (4).

  Here, rp is the internal resistance of the vacuum tube, ep is the plate voltage in the active operation state, and ip is the plate current in the active operation state. Note that rp is not a lumped constant such as a fixed resistance, but a resistance value in an active state.

  Here, the power amplifier of this embodiment is a current-driven power amplifier, and the voltage amplification degree (gain) is always 1. Then, since ep is a function of voltage in Equation (4), it does not appear as a change in the output. Instead, it can be understood that the rp information can be taken out of the vacuum tube depends on the plate current ip (= cathode current ik).

  The information on rp is carried on ip (ik) and transmitted to the primary inductance of the OPT (output transformer), but the magnetic polarities of both inductances in the OPT are canceled by equations (6) and (7) described later. Since the action is working, rp is apparently zero from the secondary side (load side).

  Here, the primary impedance Zp of OPT is expressed by the following equation (5).

  Here, Rdcp is the direct current resistance of the primary inductance (first coil) and the direct current of the second coil. In addition, since both are wound by the bifilar and show the exact same value, Rdcp and Rdck are the same value. ωLp is a reactance determined by an angular velocity (ω = 2πf) and a primary inductance (Lp), (Lk) at a certain frequency.

  The active plate current ip and the cathode current ik are energy sources that transmit an AC signal to the primary inductance of the OPT, but the behavior of both currents also acts to cancel the magnetic polarity of the primary winding. Since a reverse polarity voltage corresponding to the current change occurs, it can be expressed by the following equations (6) and (7).

  Here, e is an AC electromotive force generated at both ends of the inductance, L is an inductance of the winding, i is a signal current (AC current), and t is a time change of the signal current. Since ip and ik flow through the first coil and the second coil, the voltage appearing at both ends of both windings is expressed by the following equation.

  Here, eo is the AC electromotive force generated at both ends of the inductance, Lp is the inductance of the first coil, Lk is the inductance of the second coil, -ip is the plate current, ik is the cathode current, and t is the time change of the signal current. Represents.

  In equation (7), the values of the first term and the second term are the same, but it can be understood that since the current value of the first term is a negative sign, both are deducted, that is, the primary impedance. Of these, the reactance component is not visible from the secondary side.

  Similarly, since the rp information is also carried to the first coil and the second coil by (−ip) and (ik), if the current is applied to the equation (6), the second side is canceled similarly. No rp information appears in the output voltage to.

  The inductance component included in the equation (7) is canceled by the counter electromotive force generated in the inductance of the equation (6). On the other hand, the DC resistance Rdc existing in the inductance irrelevant to the frequency function included in Zp and Zk in the equation (5) remains as it is.

  Therefore, the primary impedance that can be seen from the secondary side is only the DC resistance value in the coil, which is a pure resistance (the slight resistance value of the wiring wire is ignored). That is, only the value of Rdc is transmitted as the primary impedance to the secondary side through OPT. This value becomes the output impedance and is related to the DF value.

The output impedance Z _O (here, Z _O1 ) of the power amplifier according to the present embodiment is expressed by Equation (8).

  Here, Rdcp and Rdck are the DC resistance values of the primary winding on the OPT plate side and the cathode side, respectively, and both are the same value, so they are expressed as Rdc, and Rm is a current monitoring resistor inserted in series with the cathode winding. (Generally 0.1Ω). μ is a voltage amplification factor of the vacuum tube, N is a winding ratio of the primary and secondary windings of OPT, and β is a current feedback coefficient. In the power amplifier of this embodiment, the loads of Lp and Lk are connected in series to the vacuum tube, but since both are bifilar windings, the inductances are exactly the same value. Therefore, since current feedback is applied only to the cathode side, β = 0.5.

In the power amplifier according to the present embodiment, it is assumed that Rdcp and Rdck have the same resistance value (Rdc) by bifilar winding. Then, the equation (8) can be rewritten as the following equation (9) (here, Z _O0 ).

  In many cases, a multipolar tube (for example, a pentode or a beam quadrupole tube) generally does not disclose a voltage amplification degree μ (particularly, μ of the multipole tube is expressed as μp). Instead, the following equation (10) is approximated from the measured plate current Ip and the second grid current Ig2 from μg1g2 (also expressed as μt as a voltage amplification factor of a triode formed between g1 and g2) disclosed. Can be calculated.

  Next, a calculation formula of DF of a power amplifier including a push-pull circuit as an application circuit is shown. The application circuit includes two vacuum tubes, four coils on the primary winding side, and two current monitor resistors (Rm). An outline of the operation of the application circuit will be described later.

The following equation (11) is a calculation formula of the output impedance Z _O of the application circuit (e.g. see FIG. 5). When a multipolar tube is used, μp may be used instead of μ.

  Here, in addition to the variables included in the equations (8) to (9), the number of vacuum tubes T is added. In an application circuit to be described later, the current feedback coefficient β is 0.5 and the number of vacuum tubes T is 2. Therefore, the denominator can be simplified as in the following equation (12).

1.5.4. Use of Horizontal Deflection Output Tube The type of vacuum tube included in the power amplifier of this embodiment is not particularly limited, but a horizontal deflection output tube may be used.

  As described above, the power amplifier of this embodiment performs power amplification by current drive. Therefore, the vacuum tube may be, for example, a horizontal deflection output tube (Sweep tube) capable of flowing a large current or a transmission tube. The horizontal deflection output tube is used for, for example, a TV cathode ray tube or the like for sweeping from a small current to a large current, and has high resistance against overload.

  Therefore, for example, when a horizontal deflection output tube or a transmission tube is used in the power amplifier of the present embodiment, long-term reliability can be ensured.

1.5.5. Experimental Results Experimental verification was performed using a beam quadrupole tube (manufactured by Philips) as the vacuum tube EL509. The vacuum tube is a horizontal deflection output tube of a color television. Since the voltage amplification degree (μp) is not disclosed by the manufacturer, μg 1 g 2 of the formula (10) was calculated as an average value 3.5 of the tube loss of the 30 W class plate loss.

  From the measured plate current Ip = 360 [mA] and Ig2 = 18 [mA] in Equation (10), μp = 70.0 was obtained. Since the plate voltage was 84.6 [V], the internal resistance rp was 235 [Ω] (84.6 [V] / 360 [mA]).

Furthermore, the measured DC resistance value of the primary inductance was Rdcp = 7.1 [Ω]. The winding ratio N can be obtained by opening a value obtained by dividing the primary impedance (in this case, pure resistance 7.1Ω) by the secondary impedance (in this case 8Ω as the impedance of the load speaker) by the square root. If you know the exact number of turns when making the transformer, you can use that value. Here, since the winding ratio N was 5.4, the output impedance Z _O = 0.0801 [Ω] was obtained from the equation (9). Therefore, the theoretical value DF is Z ₁ / Z 2 _O = 8 / 0.0801 = 99.9 according to the equation (2).

  In this experiment, a value of 108 is obtained as the actual measurement value, and since it approximates the value calculated from the above formulas (1) to (10), it can be determined that the theoretical formula is correct.

In addition, when calculating DF by applying to a theoretical formula, it is possible to measure voltage, current, resistance value, and the like with a certain accuracy by using today's digital measuring instrument. Therefore, the DF can be obtained accurately with this method. In addition, when the transformer turns ratio is unknown, AC voltage (for example, 1 kHz sine wave) is applied to the primary winding and the voltage across the secondary winding is measured, so that the voltage ratio corresponds to the winding ratio. Therefore, it is possible to easily obtain N.

  Note that the resistance insertion method (On-Off method) was employed for the actual measurement of the damping factor, and an output signal of 1 W at 1 kHz was given to an 8Ω dummy load. The DF value obtained here is a value in a so-called open loop circuit in which the overall negative feedback of the entire amplifier is not applied. Since the average value of the damping factor value of an amplifier to which negative feedback is applied by a general A1 single amplifier is about 2.5 to 8.0, the high damping factor value obtained in this embodiment is worthy of evaluation.

  Although only one power amplifying element (vacuum tube) was used in this experiment, a power amplifier having such a high DF could be easily constructed. In addition, it is easy to know in advance the numerical values (parameters) such as the winding ratio (N) of the OPT, the DC resistance (Rdc) of the primary winding, and the current amplification factor (μ) of the vacuum tube. It has become possible to design and manufacture amplifiers with arbitrary DF values from the design stage, which has been considered difficult with amplifiers.

2. Second Embodiment A second embodiment of the present invention will be described with reference to FIGS. The power amplifier according to the second embodiment includes a push-pull circuit that combines two basic circuits of the amplifier transformer for the first embodiment. In the second embodiment, in addition to the characteristics in the first embodiment, the distortion canceling action by the push-pull operation acts more strongly, and the mutual (total conductance, M) acts strongly between the primary inductances, and the frequency characteristics are remarkably improved. There is an improvement effect such as.

2.1. First Application Circuit FIG. 5 is a diagram illustrating an example (first application circuit) of a power amplifier circuit including a push-pull circuit provided with two sets of load windings in the amplifier circuit transformer. The first application circuit inputs signals having opposite phases (signals 100A and 100B) to the two vacuum tubes 34-1 and 34-2 to perform a push-pull operation.

  The first application circuit includes a phase inversion circuit 50 in order to generate a signal having a reverse phase based on the input signal 100. A specific configuration of the phase inversion circuit 50 will be described later.

  The power amplifier 1A including the first application circuit includes amplifier circuit transformers 10-1 and 10-2 having bifilar windings in two primary windings sharing the secondary winding 22, and two amplifier circuits. 30-1 and 30-2 are combined. The amplifier circuit transformers 10-1 and 10-2 correspond to the amplifier circuit transformer 10 of FIG. 1, and the amplifier circuits 30-1 and 30-2 also correspond to the amplifier circuit 30 of FIG. The amplifier circuits 30-1 and 30-2 may include an input resistance. The secondary side has the same configuration as that of the amplifier circuit transformer 10 in FIG. Instead of two sets of bifilers, a set of quadfiler windings may be provided.

  The amplifier circuit transformer 10-1 uses the output from the plate side of the vacuum tube 34-1 of the amplifier circuit 30-1 as the first amplified signal 102-1, and from the cathode side of the vacuum tube 34-2 of the amplifier circuit 30-2. Is the second amplified signal 104-2. The amplifier circuit transformer 10-2 uses the output from the plate side of the vacuum tube 34-2 of the amplifier circuit 30-2 as the first amplified signal 102-2, and outputs the output from the cathode side of the vacuum tube of the amplifier circuit 30-1. The second amplified signal 104-1 is assumed. The phase of the signal 100B input to the vacuum tube 34-2 is opposite to that of the signal 100A input to the vacuum tube 34-1.

  At this time, as described in the first embodiment, the first coil 23-1 and the second coil 24-1 on the upper side of FIG. It is like. However, in the power amplifier 1A, the second amplified signal 104-2, which is the output from the cathode side of the vacuum tube 34-2, is applied with a reverse polarity, that is, it is magnetically coupled. The same applies to the first coil 23-2 and the second coil 24-2 on the lower side of FIG.

  The second coil 24-1 and the second coil 24-2, which are the coils on the cathode side, receive signals having opposite magnetic phases and opposite phases. The signal will flow. That is, strong magnetic coupling (total conductance) occurs, and the inductance of both is the same as that connected.

  Thus, strong magnetic coupling occurs between all of the four windings, and as a result, all four windings are equivalent to being connected in series. For example, in this embodiment, since one coil has 350 mH, it is known that the inductance is proportional to the square of the number of turns. Therefore, the total inductance of four connected in series is 16 times the square of 4, Its value is 5.6H. This value is as small as about 1/20 compared to the primary inductance 100H of the output transformer of a general AB1 push-pull amplifier.

  Therefore, even if the inductance of one coil is small, the power amplifier 1A passes a large current of 300 mA to 500 mA that is much larger than the plate current of about 20 mA of the conventional AB1 push-pull amplifier (AB1-PP). . When the average value is 400 mA, an energy amount of 0.896 is obtained from the above equation (3), but the energy when the plate current 20 mA of the conventional AB1-PP is applied to 100 H is 0.04, and the relative value of both The ratio can be as large as 22.4 times, resulting in a large energy ratio. This large amount of energy 0.896 is injected into the primary winding of a 5.6H transformer connected in series by mutual magnetic coupling. Therefore, sufficient energy can be injected into the magnetic circuit, excellent frequency characteristics up to the ultra-low frequency range, and faithful signal transmission can be achieved even in a frequency band higher than the audible frequency. Ensuring low frequency characteristics even if the inductance is reduced has the advantage of reducing the DC resistance (Rdc) in the inductance, resulting in the effect of obtaining a large DF.

  FIG. 6A to FIG. 6D are diagrams showing the fault tolerance of the first application circuit. The power amplifier 1A uses two vacuum tubes, and even if one of them fails, the function as the power amplifier can be continued. 6 is the same as FIG. 5 in identifying the coils 23-1, 23-2, 24-1, 24-2 and their terminals, and the same elements are denoted by the same reference numerals. The description is omitted.

FIG. _6A is a diagram illustrating the magnetic polarities of the DC currents I _dcp1 , I _dck1 , I _dcp2 , I _dck2 and the coils 23-1, 23-2, _24-1 , _24-2 . FIG. 6A shows the physical positional relationship (direction) of the coils 23-1, 23-2, 24-1, 24-2. Here, the direct currents I _dcp1 and I _dck1 are the plate current and cathode current of the vacuum tube 34-1 respectively. The direct currents I _dcp2 and I _dck2 are the plate current and cathode current of the vacuum tube 34-2, respectively. Others are the same as those in FIG.

  FIG. 6B is a diagram showing the direction of the magnetic polarity (magnetic polarity in the active state) with respect to the AC signal of the coils 23-1, 23-2, 24-1, 24-2 when the power amplifier 1A is normal. is there. Note that the written symbols and the like are the same as those in FIG. During normal operation, in-phase synthesis is performed in each of the amplifier circuit transformers 10-1 and 10-2.

  FIG. 6C shows a state in which the vacuum tube 34-2 has failed and no longer operates. At this time, no direct current flows through the first coil 23-2 of the amplifier circuit transformer 10-2 and the second coil 24-1 of the amplifier circuit transformer 10-1.

  FIG. 6D shows the subsequent operation of the power amplifier 1A. The coil 23-2 and the coil 24-1 cannot emit magnetic energy from themselves, and receive magnetic energy from the adjacent coil 24-2 and coil 23-1 that are magnetically tightly coupled. .

  And the magnetic polarity opposite to the magnetic polarity of the coil which gave energy at that moment occurs. This is because it is a basic characteristic of inductance and generates a back electromotive force with respect to incident energy. In FIG. 6D, a state where a back electromotive force is generated and the magnetic polarities of the coils 23-2 and 24-1 are restored is indicated by “◯”. At this time, the pseudo normal operation is performed, so that the output of the music source or the like is not interrupted.

  Therefore, even if the vacuum tube 34-2 fails in the power amplifier 1A, the function as the power amplifier can be continued although there is a slight decrease in power and sound quality. This is effective, for example, when used in outdoor concerts and the like and wants to continue playing even if there is a vacuum tube failure.

2.2. Second Application Circuit FIG. 7 is a diagram illustrating another example (second application circuit) of a power amplifier circuit including a push-pull circuit in which two amplifier circuit transformers are combined. Unlike the first application circuit, the second application circuit is a push-pull by inputting in-phase signals (input signal 100) to the two vacuum tubes 34-1 and 34-2 and inverting the magnetic polarity of the inductance on the output side. It is operating. In addition, the same code | symbol is attached | subjected to the same element as FIG. 5, and the description which overlaps with a 1st application circuit is abbreviate | omitted.

  In the power amplifier 1B, magnetic coupling does not occur between the amplifier circuit transformer 10-1 and the amplifier circuit transformer 10-2 because of the magnetic polarities of the same phase. On the other hand, in the primary winding of each amplifier circuit transformer, the first coil and the second coil are magnetically coupled.

  The power amplifier 1B has a relatively high frequency characteristic because coupling due to capacitance between the first coil and the second coil and between the primary windings of the amplifier circuit transformer is significant. Move on. Therefore, it shows excellent frequency characteristics at high frequencies.

  8A to 8D are diagrams illustrating the fault tolerance of the second application circuit. Although the power amplifier 1B uses two vacuum tubes, even if one of them fails, the function as the power amplifier can be continued. 8 are the same as those in FIG. 7 for identifying the coils 23-1, 23-2, 24-1, 24-2 and their terminals. The same elements as those in FIGS. 6A to 6D are denoted by the same reference numerals, and description thereof is omitted.

  FIG. 8A is a diagram for explaining the direct current of the second application circuit and the magnetic polarity of the coil, and represents the physical positional relationship (direction). DC magnetization does not occur in each of the amplifier circuit transformers 10-1 and 10-2.

  FIG. 8B is a diagram showing the direction of the magnetic polarity (magnetic polarity in the active state) with respect to the AC signal of the coils 23-1, 23-2, 24-1, 24-2 when the power amplifier 1B is normal. is there.

  FIG. 8C shows a state in which the vacuum tube 34-2 has failed and no longer operates. At this time, no direct current flows through the first coil 23-2 of the amplifier circuit transformer 10-2 and the second coil 24-1 of the amplifier circuit transformer 10-1.

  FIG. 8D shows the subsequent operation of the power amplifier 1B. The coil 23-2 and the coil 24-1 cannot emit magnetic energy from themselves, and receive magnetic energy from the adjacent coil 24-2 and coil 23-1 that are magnetically tightly coupled. .

  And the magnetic polarity opposite to the magnetic polarity of the coil which gave energy at that moment occurs. This is the same as the first application circuit, which is a basic characteristic of inductance, and generates a back electromotive force with respect to incident energy. In FIG. 8D, the state where the back electromotive force is generated and the magnetic polarities of the coils 23-2 and 24-1 are restored is indicated by “◯”. At this time, the pseudo normal operation is performed, so that the output of the music source or the like is not interrupted.

2.3. Measurement and Discussion The damping factor was measured using the power amplifier (phase-inversion input type push-pull power amplifier) of this embodiment. Since the actual measurement value is significantly different from the value obtained from the theoretical calculation formula, it is thought that some energy that gives DF is acting in addition to the DF value obtained by the theoretical calculation formula. Added consideration.

  The calculation method of the damping factor can be obtained based on the output impedance obtained by the equation (9) or the equation (12) as described above. However, it is considered that the damping factor is not only the one given depending on the direct current resistance existing in the primary inductance described here. In the present embodiment, since the existence of a new damping factor was found from the experimental results of the toroidal core output transformer (hereinafter referred to as OPT-3) newly produced for the third time, the hypothesis will be described here.

  The aforementioned DC resistance based damping factor (DF) can be said to be a passive DF. The core capacity of the OPT-3 used was equivalent to about 10 W, and a small output transformer was manufactured using it. The circuit used was the first application circuit, and the experimental result obtained by mounting OPT-3 was a damping factor 285. The DC resistance based damping factor (hereinafter referred to as passive damping factor or passive damping factor (DFps)) obtained 152 from the theoretical calculation formula. This is significantly different from the actual measurement value 285, and there is a difference of 133 between the two. Therefore, it can be interpreted that a certain large difference in value is caused by some other energy.

  The winding ratio of the primary winding and the secondary winding of OPT-3 is 5.17, and the power amplification element used is the vacuum tube EL509. The winding ratio 5.17 is a winding ratio necessary for obtaining impedance matching between the primary and secondary of OPT-3. The primary inductance of OPT-3 was 350 mH and a quad filer was wound. The DC resistance Rdc of the primary coil was a measured value of 5.3Ω. A plate voltage of 95 V was applied to EL509, and a plate current (Ip) of 450 mA was applied. The second grid current (Ig2) was 20 mA. The current monitor resistance used was 0.1Ω. The maximum audio distortion-free output measured under these conditions was 6.5 W at 1 kHz · 8Ω.

  Compare the measured damping factor 285 with the value 152 obtained by the theoretical calculation formula. Formula (12) was used as the calculation formula, and μg1g2 was set to 3.5. When the output impedance was calculated from the above parameters, 0.0526Ω was obtained. When the load impedance (8Ω) of the speaker is divided by the output impedance, a damping factor 152 is obtained.

  It can be said that this value 152 is significantly smaller than the actual measurement value 285. Since another energy is required to generate the DF value of 133 having the difference, the following idea was taken. First, the electric power (Pin) input to the vacuum tube is 85.5 W with 95 V × 0.45 A × 2. If the plate efficiency is 45%, 85.5W × 0.45 = 38.5W. This theoretical output value of 38.5 W should be output from OPT-3. However, the core capacity of OPT-3 was 10 W, which was smaller than that, and the measured output was 6.5 W as described above. Therefore, 32.0 W obtained by subtracting the measured output 6.5 W from the theoretical output value 38.5 W is not output from the speaker terminal as the audio signal output. This power is considered to remain in the core of the OPT-3 and the output circuit, but since the output circuit such as the OPT-3 does not generate heat, it is considered that energy is consumed through some path. This residual energy 32W does not flow into the voice coil as an audio signal, but is considered to be used as new kinetic energy for driving the speaker sharply or applying a brake. The damping factor generated by this kinetic energy is tentatively called active damping factor (active damping factor (DFac)).

  Since the actual damping factor was 285 and the active damping factor was 152, it was interpreted that the difference 133 was changed to the active damping factor (DFac). The damping factor generated per 1 W from the residual energy (power) 32 W was 133/32 = 4.2.

  Active damping factor (The mechanism by which DFac is generated depends on the output capacity of the output transformer. In this experiment, an output capacity of 10 W was used, but by using a sufficiently large core for OPT, All the audio output produced can be output to the speaker, but the DF obtained in this case is only the passive damping factor (DFps), only the damping factor obtained from the DC resistance in the primary inductance, for example 152 If the above-mentioned action is actively utilized, if you want to obtain a large DF value, use an OPT with an output capacity smaller than the theoretical output value obtained from the vacuum tube. Actively generated active damping factor (DFac) Accordingly, it is possible to create a DF higher than the DC resistance dependent DFps, which can be created because the present embodiment is a current-driven power amplifier. This is an active damping factor, which is a new damping factor theory (hypothesis), a phenomenon that did not exist in conventional tube amplifiers and semiconductor amplifiers.

  The overall performance in this embodiment is reported. The final-stage output circuit used is the first application circuit (phase-inverting input type push-pull circuit). The preamplifier has a two-stage configuration. The first stage uses a shunt-regulated push-pull (SRPP) using a vacuum tube 6DJ8, and the second stage uses a similar SRPP using 6FQ7. As the phase inversion circuit, the most common PK division phase inversion circuit using a resistor, which will be described later, was used. The power supply supplies DC + 330V to the preamplifier through a pi (π) ripple filter composed of a bridge diode rectifier, a resistor and an electrolytic capacitor. The power supply for the plate voltage of the power amplifier tube is simply connected to a 2200μF electrolytic capacitor after rectification with a bridge diode, and a DC + 95V is supplied to the power amplifier tube EL-509 from a simple power source without using a ripple filter such as a choke coil. Yes. In addition, overall negative feedback is not applied to the entire amplifier.

  The damping factor is one of the items for evaluating the overall performance of the audio amplifier, and 285 was obtained as described above. Furthermore, distortion is one of the important evaluation items that determine the quality of an amplifier in terms of hearing. This is generally measured at 1 kHz and 1 W output at 8Ω, which is a pseudo load, and evaluated with a small total harmonic distortion factor (THD%). In this embodiment / first circuit diagram, the measured THD% was 0.045% for the left channel and 0.055% for the right. The difference in distortion between the left and right is thought to be due to the fact that the chassis used was an A3500 amplifier kit manufactured by Lux and the parts arrangement was asymmetrical. It is a value that can be sufficiently evaluated as a distortion factor of a power amplifier that is not subjected to overall negative feedback.

  Frequency characteristics are an important measurement item for evaluating the performance of audio amplifiers as well as distortion. The human audible frequency range is said to be 20 Hz to 20 kHz. However, it has long been said that it is necessary from 50 kHz to around 60 kHz to convey musical nuances. In fact, it is said that a major speaker manufacturer in the UK improved the audibility by extending the high frequency characteristics of the tweeter to around 60 kHz. However, it has been said that recent audio amplifiers require a response of up to 150 kHz.

  Therefore, in this embodiment, the measurement was performed while paying attention to the high frequency reproduction band of the amplifier, and the following characteristics were obtained. The measurement result was within −0.15 dB for both channels at 20 Hz in the low frequency range. At 150 kHz, the left channel was -2.1 dB and the right was -1.8 dB. Since the general frequency characteristic of the vacuum tube amplifier using the OPT is from about 30 Hz to the high range from about 50 kHz to 60 kHz, the frequency characteristic of the present embodiment deserves sufficient evaluation. The reason why almost flat characteristics were obtained up to 20 Hz in the low frequency range is that the OPT primary winding can be tightly coupled with a quad filer to obtain a large mutual coupling (total conductance).

  It was explained that the high-frequency characteristics are about 50 kHz to 60 kHz in a general vacuum tube amplifier. However, the magnetic permeability (μ) of a silicon steel plate used for a core material of OPT generally used is lower than around 20 kHz. In the vicinity of 50 kHz to 60 kHz, it becomes almost zero and does not work as a transformer. Although there are differences depending on the thickness of the core, it is said that the lower the thickness, the higher the high frequency characteristics. Still, in most core materials, μ is almost zero in the vicinity of 50 kHz to 60 kHz. Although there is such an essential problem, in this embodiment, the high frequency characteristics extend to 150 kHz. In the high range of 60 kHz to 150 kHz, the inductance as an active device using magnetic permeability (μ) is a region where it no longer works. The transmission of audio signal energy in this band should not be able to be reproduced up to 150 kHz unless another active device is interposed. An alternative active device is a capacitor. Because the insulation of the wire wound as the primary winding of the transformer acts as a dielectric, the wire insulation used in this embodiment forms an excellent capacitor with low dielectric loss between the windings. It is evidence that A capacitor is also an active device, has an action of storing electric charge (Q) in the dielectric of the capacitor (C), and transfers energy by charge transfer. The capacitor has a function of storing and transmitting energy according to the following formula.

  Here, Q represents the amount of charge, C represents the capacitance of the capacitor, and V represents voltage (voltage applied to both ends of the capacitor).

  That is, it means that energy is transferred by capacitive coupling instead of magnetic coupling. In this embodiment, as already described, a wire obtained by coating polyester and polyimide on the insulating coating material of the OPT winding wire is used. These materials work as excellent dielectrics, and as a result, capacitors with excellent high-frequency characteristics and acoustic properties were generated between the primary coil wires, and energy was transferred by the charge transfer function of the capacitors. Indicates that has been done. Signal transmission from 50 kHz to 60 kHz to 150 kHz, which was impossible only by the magnetic permeability dependence of silicon steel plates, has been made impossible by conventional tube amplifiers using an output transformer (OPT). In addition, reproduction of a high frequency of 60 kHz or higher is realized without using overall negative feedback (NFB).

  The signal to noise ratio (S / N) was measured. The left channel was 93.8 dB and the right was 88.2 dB. The difference between the measured values on the left and right is due to the asymmetric arrangement of components on the chassis as described above. However, although the S / N of the measurement result is greater than a certain value that can be evaluated, the amplifier has a sufficiently large value despite the use of a simple power source. This can be said to be a result of the direct current balance function in the output transformer working in this embodiment and the noise canceling action working correctly.

  Although the overall performance of the present embodiment is as described above, all the items show excellent characteristics that could not be obtained with the conventional vacuum tube amplifier. Finally, a hearing test was conducted as a comprehensive test. As a result, I was able to hear a wonderful sound that was soft and clear. Although it was a sensory problem, there was no audible sense of iron sound compared to general tube amps.

  The vacuum tube amplifier is said to have good sound but iron sound, but its origin is said to be due to the Barkhausen effect (phenomenon) of the physical phenomenon that occurs in the magnetic material of the core. When power (in this case, voltage) is injected from the amplifier into the core, the energy gradually increases from the low energy field in the core, and the magnetic flux in the core increases. At this time, it is said that the energy rises stepwise while breaking the magnetic barrier existing in the magnetic circuit one after another. This is because a fine step-like voltage change (tentative name Barkhausen noise) appears in the output when breaking the barrier. Since the conventional amplifier is a voltage amplification amplifier, it picks up a stepped fine signal generated from a magnetic / physical phenomenon in the core and outputs it as it is. On the other hand, since all the above embodiments are current driven amplifiers, they do not pick up Barkhausen noise, and even if they are picked up, they cancel each other out because they are a function of voltage, and iron sound ( The sound of the transformer does not appear.

3. Third Embodiment For example, the power amplifier 1A of the first application circuit requires a phase inversion circuit 50 that generates a signal in which only the phase is inverted. FIG. 9A to FIG. 9B are diagrams showing a third embodiment that embodies the phase inverting circuit 50. In addition, the same code | symbol is attached | subjected to the same element as FIG. 5, and description is abbreviate | omitted.

  First, as shown in FIG. 9A, the phase inversion circuit 50 may be formed of a PK division phase inversion circuit using a resistance load that is commonly used in vacuum tube amplifiers. By making the values of the load resistance 53 on the cathode side of the vacuum tube 52 and the load resistance 54 on the plate side the same, it is possible to obtain signals 100A and 100B having opposite phases and the same magnitude. The characteristics of the signal 100A, which is the cathode side output, are improved by a current feedback action, the output impedance is lowered, the frequency characteristics of the signal 100A are improved, and the distortion is reduced more than that of the input signal 100. On the other hand, the output impedance of the signal 100B which is the plate side output increases, the frequency characteristic becomes worse than 100A, and the distortion of the output signal increases compared to the input signal 100. In one experiment, when the distortion rate (THD) of the input signal 100 was 0.33%, the signal 100B was 0.25% and 100A was 0.45%. Therefore, the signal 100A and the signal 100B have the same voltage absolute value and opposite polarity signals, but a so-called distortion is generated between the two signals. Has inconvenience in signal quality. In addition, since the plate power supply is divided and used by the plate load resistance and the cathode load resistance, there is a disadvantage that a large output signal cannot be taken out.

  There are several circuits for phase inversion, and they have been used universally like the PK phase inversion circuit. However, other than the PK phase inversion circuit described above, the voltage amplification degree is 1 or more. Due to this feature, other circuits have been used more frequently than the PK phase inversion circuit in recent vacuum tube circuits. Other circuits include a self-balanced type, a PG inversion type (classical type), a common cathode type (also known as a mallard type), and their modified types. As described above, these have a voltage amplification degree of 1 or more, but an additional amplification circuit using a vacuum tube is added to the positive side circuit and the inverting circuit side in the signal passing path length. Therefore, it is difficult to suppress the increase in distortion, and there is no circuit whose frequency characteristic exceeds that of the PK phase inversion circuit. The distortion is mainly caused by a voltage difference between positive and reverse polarity signals. Further, since the signal path is increased by one step, phase distortion due to phase rotation due to a time constant caused by a capacitor / resistance inserted in the coupling circuit is included. On the other hand, in the PK phase inversion circuit, the signal path is the same between the bipolar output signals, and the distortion characteristics and the frequency characteristics are the best in the phase inversion circuit. One difference is known that there is a difference in the output impedance between the cathode and the plate. Although there are some differences depending on the vacuum tube to be used, in a general triode, the cathode side is about 1 to 2 kΩ, and the plate side is about 10 kΩ to 20 kΩ. If the difference is about this value, it is considered that a substantial defect does not occur unless the wiring is routed for a long time in the mounting technology. Therefore, at present, it can be said that the PK phase inversion circuit is excellent in physical characteristics (audio characteristics).

  As described above, the distortion characteristics and frequency characteristics of the power amplifier circuits in all the embodiments are far superior to those of the conventional phase inverter circuit including the PK division circuit. This causes an unreasonable effect of degrading the overall characteristics of the amplifier if a signal having inferior characteristics is sent to the power amplifier at the front stage than the output circuit at the final stage. This proposal was made in view of these unreasonableness.

  Here, the cathode-side signal 100B is in phase with the input signal 100, and the plate-side signal 100A is in reverse phase with the input signal 100.

  Here, the phase inverting circuit 50 of FIG. 9B may be used in which the load resistors 53 and 54 of FIG. 9A are replaced with the first coil 57 and the second coil 58, respectively. Since both coils are wound by a bifilar around the same core, they are electromagnetically coupled tightly. This circuit has the same structure as the bifilar winding of the primary winding of the output transformer of the basic circuit.

  In the phase inversion circuit 50 of FIG. 9B, since a large amount of current feedback is applied to the cathode side of the vacuum tube 52, some characteristics are improved, and the distortion of the signal 100B is improved to improve the characteristics. Suppressed below strain. At this time, the signal 100A on the plate side also reflects the signal 100B having a small distortion and the same distortion rate because the magnetic coupling between both coils is dense and the signal 100B having a small distortion on the cathode side is reflected. Can be generated. In addition, the frequency characteristic is improved by the characteristic improvement effect. As a result of the experiment in the present embodiment, when the distortion rate (THD) of the input signal is 0.33%, the THD of the signal 100A and the signal 100B, which are the outputs of the phase inversion circuit, is improved to 0.20%. It is possible to send an output signal of the same quality to the power output circuit.

  In the PK phase inversion circuit, the output impedance on the cathode side is different from that on the plate side. Therefore, there is a difference in the frequency characteristics and distortion of the output signals from both nodes. In this embodiment, the so-called mutual (M), in which the loads of both nodes have the same inductance that is bifilar-wound and is electromagnetically tightly coupled, acts strongly. This is considered that there is one aerial inductance (coil) M when looking at the vacuum tube side from the signals 100A and 100B side, and it is considered that both outputs share M and take out the output. Therefore, it is considered that the output impedance is the same at both nodes and is low on the cathode side. The phase of the output voltage is opposite in polarity, but is exactly the same voltage, and the distortion rate is improved and reduced to produce a signal with exactly the same distortion rate. The frequency characteristics are the same, and the high frequency characteristics have a transmission band of 150 kHz or more because of low impedance. In addition, since the voltage drop between the plate and the cathode is reduced by using the inductance, the utilization efficiency of the plate power source is improved, and there is an improvement effect that a large output signal can be taken out.

  A circuit having such an excellent phase reversal characteristic has not existed in the past, and the technology that guarantees this performance lies in the inductance of bifilar winding on both the cathode and plate nodes. Since this inductance does not take out the output by magnetic coupling on the secondary side, it simply works as a choke coil. Therefore, it is appropriate to call this circuit a choke type phase inverting circuit.

  Although this circuit is a circuit using a choke coil, an intermediate transformer (interstage transformer, IST) may be formed by winding a secondary coil capable of extracting a voltage on the secondary side around a core. By providing an intermediate tap in the secondary winding, signals having a phase difference of 180 degrees between the two terminals can be taken out, so that it may be used as a driver of a push-pull power amplifier.

  The phase inversion input type push-pull circuit, which is the first application circuit, may be configured by using the phase inversion circuit of the present embodiment. In that case, many coils may be wound for high impedance coupling on the secondary side, and impedance matching with the power amplifier tube may be taken. A transformer drive type phase inverting circuit can be constructed by winding an inductance with an intermediate tap on the secondary side, and a two-stage phase inverting input type push-pull circuit can be constructed with a driver stage and a power amplification stage. An even lower distortion power amplifier can be constructed.

4). Fourth Embodiment A fourth embodiment of the present invention will be described with reference to FIG. The power amplifier 1C of the fourth embodiment is obtained by replacing the vacuum tube with a power amplification transistor (power transistor) in the amplifier circuit of the power amplifier (see FIG. 2) of the first embodiment. In addition, the same code | symbol is attached | subjected to the same element as FIGS. 1-9 (B), and description is abbreviate | omitted.

  In FIG. 10, a power transistor 36 is used as an amplifying element of the amplifying circuit 30B. Among semiconductor devices, a transistor which is a current amplification element can be used in place of a vacuum tube because of its operation principle. In particular, the transistor has a large current amplification factor (hfe) (for example, around 100), and a high-performance power amplifier can be constructed. A power type field effect transistor (power MOS-FET) may be used instead of the transistor (bipolar) of the current amplifying element. The MOS-FET is a voltage amplification element, but may be operated as a current-driven power amplifier on the same operating principle as the vacuum tube type power amplifier described above.

  In addition, by using a power transistor instead of a vacuum tube, it is possible to reduce the size, to construct a very small amplifier, and to provide a power amplifier with a high damping factor. The power amplifier constructed with transistors can be applied to the first application circuit, the second application circuit, and the phase inversion circuit of the third embodiment.

5. The present invention is not limited to these examples, and the present invention includes substantially the same configuration (for example, a configuration having the same function, method and result, or a configuration having the same purpose and effect) as the configuration described in the embodiment. . In addition, the invention includes a configuration in which a non-essential part of the configuration described in the embodiment is replaced. In addition, the present invention includes a configuration that exhibits the same operational effects as the configuration described in the embodiment or a configuration that can achieve the same object. Further, the invention includes a configuration in which a known technique is added to the configuration described in the embodiment.

DESCRIPTION OF SYMBOLS 1,1A, 1B, 1C ... Power amplifier, 10, 10-1, 10-2 ... Transformer for amplifier circuit, 10A ... Partial circuit of transformer for amplifier circuit, 21 ... Primary winding, 22 ... Secondary winding, 23, 23-1, 23-2, 57 ... first coil, 24, 24-1, 24-2, 58 ... second coil, 30, 30-1, 30-2, 30A, 30B ... amplifier circuit 32 ... Input resistance 34, 34-1, 34-2, 52 ... Vacuum tube, 34A ... Vacuum tube (pentode), 36 ... Bipolar transistor, 38, 53, 54 ... Resistance, 40 ... Output unit, 50 ... Phase Inverting circuit, 100 ... input signal, 100A, 100B ... signal, 102, 102-1 and 102-2 ... first amplified signal, 104, 104-1 and 104-2 ... second amplified signal

Claims (9)

An amplifier circuit transformer comprising a primary winding and a secondary winding wound around a core, wherein the primary winding receives an amplified signal of the amplifier circuit;
Receiving the first amplified signal and the second amplified signal obtained by inverting the phase of the first amplified signal as the amplified signal;
The primary winding includes a first coil having one terminal connected to a first potential and the other terminal receiving the first amplified signal, and a first terminal having a lower potential than the first potential. A second coil connected to the potential of 2 and having the other terminal receiving the second amplified signal,
The inductance of the first coil and the inductance of the second coil are the same,
The first coil and the second coil are arranged such that their magnetic polarities are opposite to each other;
The core is an amplifier circuit transformer that does not include an air gap. The amplifier circuit transformer according to claim 1,
An amplifier circuit transformer in which the first coil and the second coil are bifilar wound. A transformer for an amplifier circuit according to any one of claims 1 to 2,
A power amplifier including the amplifying circuit, wherein the amplifying element is a vacuum tube. The power amplifier according to claim 3, wherein
The amplifier circuit is
A power amplifier using a horizontal deflection output tube as the vacuum tube. The power amplifier according to any one of claims 3 to 4,
A power amplifier that uses the output from the plate side of the vacuum tube as the first amplified signal and the output from the cathode side of the vacuum tube as the second amplified signal. A transformer for an amplifier circuit according to any one of claims 1 to 2,
A power amplifier including the amplifier circuit, wherein the amplifier element is a bipolar transistor. The amplifier circuit transformer according to claim 1,
A first transformer and a second transformer, which are the two transformers for an amplifier circuit according to claim 1;
A first amplifying circuit and a second amplifying circuit, wherein the two amplifying circuits and the amplifying element is a vacuum tube;
In a power amplifier including a phase inverting circuit that generates signals whose phases are inverted to each other,
Sharing the secondary winding of the first transformer and the secondary winding of the second transformer;
The phase inverting circuit is
Based on the input signal, a first signal and a second signal obtained by inverting the phase of the first signal are generated.
The first transformer is
The first signal is the grid signal of the vacuum tube,
The output from the plate side of the vacuum tube of the first amplifier circuit is a first amplified signal,
The output from the cathode side of the vacuum tube of the second amplifier circuit is a second amplified signal,
The second transformer is
The second signal is the grid signal of the vacuum tube,
The output from the plate side of the vacuum tube of the second amplifier circuit is a first amplified signal,
The output from the cathode side of the vacuum tube of the first amplifier circuit is a second amplified signal,
The magnetic polarity of the first coil and the second coil of the second transformer is opposite to the magnetic polarity of the first coil and the second coil of the first transformer. Power amplifier to be placed. A first transformer and a second transformer, which are the two transformers for an amplifier circuit according to claim 1;
In the power amplifier including the two amplifier circuits, the first amplifier circuit in which the amplifier element is a vacuum tube, and the second amplifier circuit,
Sharing the secondary winding of the first transformer and the secondary winding of the second transformer;
One input signal is the grid signal of the vacuum tube of the first amplifier circuit and the grid signal of the vacuum tube of the second amplifier circuit,
The first transformer is
The output from the plate side of the vacuum tube of the first amplifier circuit is a first amplified signal,
The output from the cathode side of the vacuum tube of the second amplifier circuit is a second amplified signal,
The second transformer is
The output from the plate side of the vacuum tube of the second amplifier circuit is a first amplified signal,
A power amplifier using an output from the cathode side of the vacuum tube of the first amplifier circuit as a second amplified signal. The amplifier circuit transformer according to claim 1,
The primary winding and the secondary winding are:
Transformer for amplifier circuit coated with polyimide coating in addition to polyester insulation.

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