JP2732830B2 - Electron tube coupling circuit using transformer - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for connecting electronic circuits. In particular, a transformer (with a magnetic iron core for audio frequency band) is connected to an electron tube (power tube) that applies a positive potential bias to the control grid to perform an AC signal power amplifying operation and a preceding AC signal source (driver tube). Interstage transformer). 2. Description of the Related Art FIG. 1 shows a circuit for applying a positive potential bias to a control grid of an electron tube to amplify an AC signal.
A dynamic couple as shown in FIG.
In this known circuit, a front electron tube 7 that provides a cathode potential equivalent to the control grid positive potential required by the electron tube 8 is used. At this time, the front electron tube 7 includes an electron tube 8
When the cathode potential 1 (= Ek) equal to the control grid positive potential 2 (= + Eg) is applied to the electron tube 8
It is necessary to select a coupling electron tube having special characteristics such that a cathode current (= Ik) equivalent to the control grid current (= Ig) flows. In the circuit configuration shown in FIG. 1, the type of the front electron tube 7 that can be actually used is limited since the coupling front electron tube 7 having characteristics satisfying the above-described special conditions must be employed. Therefore, the types of the electron tubes 8 that can be actually used are also limited. [Second Prior Art] FIG. 2 of Japanese Patent Publication No. 32-10413 discloses an example of a last stage tube which can be seen as operating with a positive grid bias like the electron tube 8 in FIG. In FIG. 2 of Japanese Patent Publication No. 32-10413, a part of the high frequency voltage generated in the plate coil of the final stage tube is rectified by the rectifier tube G, and a negative DC voltage proportional to the high frequency voltage is supplied to the low frequency modulation tube M The output is fed back to the grid (since the filament side of the rectifier tube G has a positive voltage output, the grid feedback voltage of the modulation tube M has a relatively negative voltage). This feedback modulates the final stage tube additionally (see the second paragraph in the right column on page 1 of the publication). In the circuit configuration of FIG. 2 of Japanese Patent Publication No. 32-10413, a coupling transformer (with a core as viewed from the symbol in the figure) is inserted between the modulation tube M and the final stage tube. It is recognized that the core of this coupling transformer can be DC magnetized by both the plate current of the modulation tube M and the grid current of the output tube (the specification of this publication does not describe any DC magnetization of the coupling transformer). Therefore, it is estimated from the description method of the transformer winding in FIG. 2 and the modulation tube plate current direction and the final tube grid current direction). In this case, if the core of the coupling transformer is small and the magnetic circuit of the core is not sufficiently provided with a gap for preventing magnetic saturation, this core will be able to reduce the plate current of the modulation tube M and the grid current of the output tube. Both are DC magnetized and the primary inductance of the coupling transformer is significantly reduced (because the effective permeability of the iron core is greatly reduced). Then, it becomes difficult for this coupling transformer to pass a low-frequency modulation signal, and the low-frequency response of the high-frequency modulation signal output from the final tube deteriorates. To improve this low-frequency response, the coupling transformer should be composed of a large number of iron cores with high magnetic permeability and high saturation magnetic flux density, and a large gap should be used to suppress the decrease in primary inductance due to the superposition of DC current. It is necessary to provide it in a magnetic circuit. This makes the coupling transformer bulky and considerably more costly. In the circuit configuration shown in FIG. 3 of Japanese Patent Publication No. 32-10413, the minus of the power supply Ua is applied to the plate of the front electron tube V, and the normal electron signal amplification (linear amplification) is performed by the front electron tube V. Is not admitted. (In order for the electron tube to perform the linear amplification operation, the plate must be always at a positive potential with respect to the cathode or the filament.) Similarly, the minus of the power supply Ua is also applied to the plate of the final stage electron tube E. Therefore, it is not recognized that normal AC signal amplification is performed by the last-stage electron tube E (there is a similar question in FIG. 2 of this publication regarding this power supply polarity). If the thick and short battery symbol is interpreted as + in this publication, the thin and long battery symbol of the grid bias Ua of the last stage electron tube E in FIG. In that case, the final stage electron tube E performs a general negative bias operation. In that case, a DC grid current exceeding a slight grid leak does not flow through the electron tube E, so that the DC magnetization due to the primary current of the coupling transformer between the electron tube V and the electron tube E is caused by the secondary DC current (electron tube current). The state of being canceled by the (E grid current) cannot occur. Assuming that a large current flows through the grid of the electron tube E, it means that a large amplitude AC voltage +
Although only when a peak is added, such a state is different from a state in which “the DC magnetization due to the primary current of the coupling transformer is canceled by the secondary DC current”. In addition, the coupling transformer shown in FIG. 3 of this publication has a resonance circuit (tank circuit) formed by a capacitor on the primary side, and the description in the specification deals with high frequencies. Transformer for transmitting "high frequency" signals. In other words, this transformer does not necessarily need to have an iron core (it can be seen from the drawing symbols as a high-frequency transformer having an air-core coil). Even if this transformer contains an iron core (ferrite core for high frequency), its primary winding is
In order to secure the high frequency resonance frequency of the tank circuit, the tank circuit is configured by a coil having a small number of turns that provides a small inductance of less than millihenry. In that case, the magnetomotive force of the primary winding is extremely small at a plate current of the order of milliamps of the front-stage electron tube V, and the problem of low-frequency response deterioration caused by DC magnetic saturation of the transformer core is at least as high as that described in this publication. I can't imagine). [Third Prior Art] FIG. 2 of Japanese Patent Application Laid-Open No. 58-196705 discloses an example in which a final tube operated with a clearly "negative" grid bias is disclosed. In the circuit configuration shown in FIG. 2 of Japanese Patent Application Laid-Open No. 58-196705, the secondary winding of the cored coupling transformer T is directly connected to the grid of the output tube V2 which is "negatively biased". For this reason, only a DC current (normally several μA to several tens μA or less) of the grid leak level of the electron tube negatively biased flows through the secondary winding of the transformer T. On the other hand, a plate direct current (several mA to several tens mA) of the drive tube V1 flows through the primary winding of the transformer T. That is, the primary winding DC current and the secondary winding DC current have different current values by three digits. Usually, in a low-frequency coupling transformer, the primary to secondary turns ratio is at most about 10 or less. Therefore, if the current is different by three digits, the effect of reducing the degree of magnetic saturation of the iron core of the coupling transformer T (primary DC current (The effect of canceling the magnetization due to the secondary direct current). In order to bring about the above-mentioned effects,
There is no description in JP-A-58-196705 about how to set the turns ratio of the coupling transformer T, the primary to secondary current values, and the primary to secondary current directions. Problems to be Solved by the Invention
No. 413 or JP-A-58-196705, in which the coupling transformer used therein is replaced by a low-frequency transformer having a relatively large primary inductance in order to ensure a good low-frequency response. View. In this case, unless a sufficient gap is provided in the magnetic circuit of the core of the transformer to prevent magnetic saturation, the core is DC-magnetized by the plate current of the previous driving tube,
The primary inductance of the coupling transformer is significantly reduced.
This makes it difficult for the coupling transformer to pass a low-frequency modulated signal, resulting in poor low-frequency response. To improve the low-frequency response, the coupling transformer should be composed of a large number of iron cores with high magnetic permeability and high saturation magnetic flux density, and a large gap should be used to suppress the decrease in primary inductance due to the superposition of DC current. It must be provided in the circuit. Then, the coupling transformer becomes large and expensive. An object of the present invention is to use a coupling transformer instead of the coupling front electron tube 7 as shown in FIG. 1 to control an arbitrary positive voltage for any type of electron tube 8. An object of the present invention is to provide an electron tube coupling circuit using a transformer, which can be used in a state in which an arbitrary grid current is supplied to a grid and used. In order to achieve the above object, according to the present invention, a primary winding (13) and a secondary winding (AC) that is AC-coupled to the primary winding (13) are provided. A transformer (11) of FIG. 2; a first DC power supply (16) connected to a first DC power supply (16) through a primary winding (13) of the transformer (11); A pre-stage AC signal source (9) for flowing a DC current (14) through a primary winding (13) of the transformer (11); and a secondary winding (12) of the transformer (11).
And a grid connected to a second DC power supply (10) for flowing a second DC current (4) to a secondary winding (12) of the transformer (11) via a predetermined load (18). A third current (19) connected to a third DC power supply (17) and changing in response to a voltage change occurring in the secondary winding (12) of the transformer (11) to the load (18). And an electronic tube (8) having a flowing plate, wherein said transformer (1) is generated by said first direct current (14) flowing through a primary winding (13) of said transformer (11).
The direction in which the second DC current (4) flows with respect to the secondary winding (12) of the transformer (11) is determined so that the degree of DC magnetization in 1) is canceled or reduced. I have. Here, the connection polarity (grid side +) of the second DC power supply (10) to the transformer secondary winding (12) is such that the grid of the electron tube (8) is connected to its cathode or filament. Is determined to be biased to a positive potential. Also, the plate of the electron tube (8) is biased to a positive potential with respect to its cathode or filament. Referring now to the drawings, a description will be given of a coupling circuit of an electron tube using a transformer according to an embodiment of the present invention. In order to avoid redundant description, common reference numerals are used for functionally common parts in a plurality of drawings. FIGS. 2 to 4 are diagrams for explaining a coupling circuit of an electron tube using a transformer according to an embodiment of the present invention. As shown in FIG. 2, a transformer 11 is used for coupling the former-stage AC signal source 9 and the latter-stage electron tube 8 to each other.
That is, a positive potential of an arbitrary value is applied to the control grid of the electron tube 8 from the DC power supply 10 via the secondary winding 12 of the transformer 11. The plate of the electron tube 8
A high voltage positive potential of the DC power supply 17 is applied via a load element 18 (such as an output transformer). The magnitude of the plate current 19 flowing from the power supply 17 to the plate of the electron tube 8 through the load element 18 changes according to the voltage induced in the secondary winding 12 of the transformer 11. In FIG. 2, when the power supply 16 for the preceding-stage AC signal is positively connected (the power supply output with respect to the ground is positive), the DC current 1 flowing through the primary winding 13 of the transformer 11 is
The current direction and wiring of each of the grid current 4 flowing through the secondary winding 4 and the secondary winding 12 of the transformer 11 are shown by solid arrows. In FIG. 2, when the power supply 16 for the pre-stage AC signal is negatively connected (power supply output with respect to the ground is negative), the DC current 14 flowing through the primary winding 13 of the transformer 11 and the two The current direction and wiring of each of the grid currents 4 flowing through the secondary winding 12 are indicated by broken arrows. In the embodiment shown in FIG. 2, since the pre-stage AC signal source 9 and the control grid of the electron tube 8 are DC-separated by the transformer 11, the conditions "Ek = + Eg" and the condition described in FIG. It is not necessary to use a coupling electron tube having characteristics satisfying “Ik = Ig” for the preceding AC signal source 9. Therefore, what kind,
It will be possible to use even electron tubes with special characteristics. In FIG. 2, the secondary winding 12 has a direction opposite to the DC current 14 flowing through the primary winding 13 of the transformer 11.
By selecting the connection of the secondary winding 12 so that the DC grid current 4 flows through, the core of the transformer 11 (in the transformer symbol in the figure, two vertical bars indicate that the transformer is a cored transformer) Is reduced (or negated). As a result, the iron core of the transformer is less likely to be magnetically saturated, and its primary inductance can be increased, so that the distortion factor and frequency response characteristics of the transformer can be improved. FIG. 3 shows an example of a typical electron tube designed for high-frequency output / oscillation and class B amplification / output.
The plate voltage of the RCA-830-B type electron tube (PL
ATE VOLTS) vs. plate current (PLATE A)
(MPERS) is shown. Unlike an electron tube designed and manufactured for the main purpose of class A amplification and output (a wide operating region at a control grid negative potential), as shown in FIG. The operating area at the potential is narrow, and conversely, the operating area at the control grid positive potential is very wide. FIG. 4 shows a case where an electron tube "RCA-830B" having the above-described characteristics is applied to the present invention. Here, a positive voltage is applied from the DC power supply 10 to the control grid of the electron tube 8 (RCA-830B) through the secondary winding 12 of the transformer 11 to flow the grid current Ig4, and the control circuit is connected to the preamplifier circuit (electron tube 6F6). Let's combine
Electron tube 8 (R
CA-830B) in a single operation. According to this circuit, a maximum output power of 18 W can be obtained. The circuit according to the present invention is a single operation of the electron tube 8 designed for amplification and output of class B and class C having good amplification linearity in the control grid positive potential region, thereby providing an AC signal having good input / output linearity. It is particularly effective for performing amplification. However, the circuit of the present invention can also be applied to a push-pull operation in which a positive potential is applied to the control grid. In this case, it is possible to avoid the occurrence of switching distortion, which is conventionally unavoidable during class B and C push-pull amplification. According to the present invention, a positive potential is applied to the control grid of an electron tube designed for amplification and output in a control grid negative potential region, and the control grid is operated with a low plate voltage and a large cathode current (large plate current). Can also be used. According to the present invention, since there is no coupling front electron tube having appropriate characteristics in the past, a single operation for amplification or output of an audio low-frequency amplifier requiring low distortion is required. An electron tube with a wide operating area at the control grid positive potential (for example, RC
A-830B type electron tube) can be easily used under optimal operating conditions. Further, low frequency output power (usually at most about 8 W to 10 W), which is a drawback of a single operation output type audio low frequency amplifier using a direct heat type electron tube, which is preferably used because of its sound quality. ) Is eliminated by the present invention. That is, high-frequency output for large output,
The use of a direct-heat type electron tube designed for oscillation, class B amplification, and output in a single operation makes it possible to obtain a low-distortion low-frequency output. The frequency output power can be obtained by a single operation (for example, an output power of up to 18 W can be obtained in the example of FIG. 4).

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a circuit diagram illustrating a so-called dynamic couple circuit (known in the art) for applying a positive potential to a control grid using a coupling front electron tube. FIG. 2 relates to an embodiment of the present invention,
FIG. 2 is a circuit diagram in which the coupling front electron tube of FIG. 1 is eliminated and a coupling transformer is used instead. FIG. 3 is a characteristic diagram of an example (RCA-830B) of an electron tube designed and manufactured for high-frequency output, oscillation, and class B amplification and output that can be used in the present invention. FIG. 4 is a circuit diagram showing a specific example of an audio low-frequency power amplifier circuit using a RCA-830B type electron tube as a single-stage electron tube (output tube). [Description of Signs] 8: Rear electron tube or power tube (830B); 4: Grid current Ig of rear electron tube; 19: Plate current Ipp of rear electron tube; 9: Front AC signal source or front electron tube or driver tube (6F6); 14: Plate current (first DC current) Ip of front electron tube; 10: DC power supply (second DC power supply) for grid current supply of rear electron tube; 11: Low frequency transformer (NC-10); 12: Transformer Secondary winding;
13: primary winding of transformer; 16: first DC power supply (B +
230V); 17 ... third DC power supply (B + 480V);
18 Load (output transformer; X-3.5S).

Claims (1)

(57) [Claims] 1. Primary winding and AC coupled to this primary winding
A transformer with a secondary winding; Connected to a first DC power supply via a primary winding of the transformer.
A first direct current, on which an alternating current component is superimposed,
A pre-stage AC signal source flowing through the primary winding; Connected to a second DC power supply via a secondary winding of the transformer.
A second DC current flowing through the secondary winding of the transformer.
Connected to a third DC power supply via a predetermined load.
Changes in response to the voltage change in the secondary winding of the transformer.
A plate for passing a third current through the load,Emits electrons
With cathode or filamentAn electron tube with
In the provided,The grid of the electron tube is its cathode or filament.
The second voltage is biased to a positive potential with respect to
The connection polarity of the DC power supply to the transformer secondary winding is determined.
Done; The plate of the electron tube is its cathode or filament.
Biased to a positive potential with respect to The first direct current flowing through the primary winding of the transformer
The degree of DC magnetization of the transformer where
Secondary winding of the transformer so that
The direction in which the second DC current flows is determined
An electronic tube coupling circuit using a transformer.