The present invention relates to a vacuum tube which operates as an analog amplifier.
A vacuum fluorescent display is known as a technique related to a vacuum tube, and, for example, structures shown in Japanese Utility Model Publication No. 49-5240 (hereinafter referred to as “Patent Literature 1”) and Japanese Patent Application Laid Open No. 2007-42480 (hereinafter referred to as “Patent Literature 2”) are known. In Patent Literature 1, a linearly tensioned filament which emits thermoelectrons at a predetermined temperature or higher is referred to as “a heater H”. An anode arranged parallel to the filament (“a positive pole 4” in Patent Literature 1), and a grid arranged between the filament and the anode such that the grid faces the anode are provided (see FIGS. 1 and 2 of Patent Literature 1). A basic structure in Patent Literature 2 is the same as that of Patent Literature 1. As a control method for the vacuum fluorescent display shown in Patent Literatures 1 and 2, a driving system shown in “Vacuum Fluorescent Display (VFD) General Application Notes—Driving Method—Driving system” by NORITAKE ITRON CORP, searched on the Internet (<https://wvvw.noritake-itron.jp/cs/appnote/apf100_vfd/apf201_houshiki.html>) on Dec. 19, 2014 (hereinafter referred to as Reference Document 1) is known.
Because there is a demand from users who like characteristics of a vacuum tube mainly in the music industry, there is a demand for a vacuum tube to be used as an analog amplifier, and a vacuum tube which can be used as an analog amplifier exists. For most of general analog amplifiers, however, a semiconductor such as a transistor and an operational amplifier is used. Therefore, the quantity of production of vacuum tubes to be used as analog amplifiers decreases, and there are problems of increase in price and difficulty in availability. On the other hand, a vacuum fluorescent display, which is a kind of vacuum tube and is available inexpensively, is digitally controlled as is known from the driving system shown in Reference Literature 1 and is not designed for use as an analog amplifier. Therefore, the vacuum fluorescent display is not easily used for analog amplification.
An object of the present invention is to provide a vacuum tube with a structure close to that of an inexpensive and easily available vacuum fluorescent display, which is easy to use as an analog amplifier for a sound signal.
The vacuum tube of the present invention comprises a filament and two pairs of a grid and an anode. The filament is tensioned linearly and emitting thermoelectrons. Both of the anodes are formed on the same face on a planar substrate. The filament is arranged parallel to the planar substrate at a position facing both of the anodes. Each of the grids is arranged, such that the grid faces the anode in the same pair at a first predetermined distance from the anode and has a second predetermined distance from the filament, between the anode and the filament. The vacuum tube of the present invention further comprises an intermediate filament fixing part fixing the filament at a position corresponding to an intermediate point between the anodes of the two pairs.
According to the vacuum tube of the present invention, it is easy to increase a fundamental frequency of vibration of the filament because the filament is intermediately fixed. In other words, since it is easy to bring noises generated by the vibration of the filament to a frequency insensible to a person, the vacuum tube is easy to use as an analog amplifier for sound signal.
An embodiment of the present invention will be described below in detail. Components having the same function are given the same reference numerals, and repeated description will be omitted.
A plan view, front view and side view of a vacuum tube of the present invention are shown in
Next, a specific example of a structure for realizing the above features will be described.
The filament 110 is a directly heated cathode. For example, the filament 110 can be coated with barium oxide so that thermoelectrons are emitted when the filament 110 is heated to about 650 degrees by causing a direct current to flow. In this example, the “predetermined temperature or higher” described above is 650 degrees, but the temperature is not limited to 650 degrees.
The filament 110 is heated by a direct current flowing and heated to a predetermined temperature at which thermoelectrons can be emitted or higher. Near the welding points 112 and the intermediate filament fixing part 113, however, the temperature of the filament 110 cannot be heated to the predetermined temperature at which thermoelectrons can be emitted or higher because of heat transfer to the filament support member 111 and the intermediate filament support member 119. Therefore, a center of each of the grids 130-1, 130-2 faces a position corresponding to ¼ of the filament 110 from one end of the filament 110 (one of the welding points 112), and the intermediate filament fixing part 113 can be located at a position that divides the filament 110 into two halves (a middle point between the two welding points 112). With such an arrangement, the filament 110 facing the anodes 120-1, 120-2 can be located at a position farthest from the filament support member 111 and the intermediate filament support member 119, and, therefore, it is possible to efficiently utilize the thermoelectrons emitted from the filament 110.
Specifically, in the vacuum tube 100, the distance between the anodes 120-1, 120-2 and the grids 130-1, 130-2 (the first predetermined distance), which is between 0.15 mm and 0.35 mm, including 0.15 mm and 0.35 mm, is realized by the grid support members 132-1, 132-2. The distance between the filament 110 and the grids 130-1, 130-2 (the second predetermined distance), which is between 0.2 mm and 0.6 mm, including 0.2 mm and 0.6 mm, is realized by the filament support members 111, the intermediate filament support member 119 and the grid support members 132-1, 132-2.
Next, the necessity of the first predetermined distance and the second predetermined distance of the present invention will be described. A general vacuum fluorescent display also comprises: a filament which is tensioned linearly and emits thermoelectrons at a predetermined temperature or higher, an anode arranged parallel to the filament, and a grid arranged between the filament and the anode such that the grid faces the anode. In the general vacuum fluorescent display, however, a distance between the anode and the grid is about 0.5 mm or more, and a distance between the filament and the grid is about 1.0 mm or more. Further, the fundamental frequency of the characteristic vibration of the filament is not considered. In the case of the vacuum fluorescent display, ON/OFF control is performed, and, therefore, it is necessary to avoid a current from flowing insufficiently when the voltage of the grid is changed. That's why the above lengths are adopted.
Further, in the case where the distance between the anodes 120-1, 120-2 and the grids 130-1, 130-2 (the first predetermined distance) exceeds 0.35 mm, it is necessary that the grid support members 132-1, 132-2 are bent-formed. On the other hand, if the distance between the anodes and the grids (the first predetermined distance) is between 0.15 mm and 0.35 mm, including 0.15 mm and 0.35 mm, the grid support members 132-1, 132-2 can be configured only by performing blanking of flat board. In this case, since the distance between the anodes and the grids is determined by the board thickness of the grid support members, the grid support members 132-1, 132-2 can be formed with an accurate distance. Further, if the grid support members 132-1, 132-2 are bent-formed, the grids easily vibrate and cause noises. If the grid support members 132-1, 132-2 are formed by flat board punching, the vibration of the grids can be suppressed, and a vacuum tube which is easy to utilize for analog amplification can be obtained.
Further, as described above, if the filament is intermediately fixed, the wavelength of the vibration of the filament can be shortened, and, therefore, it is easy to increase the fundamental frequency of vibration of the filament. In other words, since it is easy to bring the frequency to a frequency insensible to a person, the vacuum tube is easy to use as an analog amplifier for sound signal. If the frequency of the characteristic vibration of the filament 110 is increased to 3 kHz or higher, noises resulting from the vibration of the filament 110 can be brought to a frequency inaudible to a person. Such frequency adjustment can be realized by adjusting material and thickness of the filament 110, the length from the welding points 112 to the intermediate filament fixing part 113 and the tension given by the anchors 115. It is desirable that the fundamental frequency is high, and if the fundamental frequency can be adjusted to be 10 kHz or higher, it is possible to prevent noises due to the vibration of the filament from being heard by a person.
Number | Date | Country | Kind |
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2015-008346 | Jan 2015 | JP | national |
This is a continuation application of U.S. patent application Ser. No. 15/000,353, filed on Jan. 19, 2016, which claims the benefit of Japanese Patent Application No. 2015-008346, filed on Jan. 20, 2015. The entire disclosure of each of the above-identified applications, including the specification, drawings, and claims, is incorporated herein by reference in its entirety.
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Noritake Itron Corporation, “Guide to VFD Operation Application Note Drive Characteristic”, Dec. 19, 2014, https://www.noritake-itron.jp/cs/appnote/apf100—vfd/apf201—houshiki.html. |
U.S. Appl. No. 15/000,392 to Kazunori Tatsuda et al., which was filed on Jan. 19, 2016. |
Number | Date | Country | |
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Parent | 15000353 | Jan 2016 | US |
Child | 15388328 | US |