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Vacuum Tube Amplifier

Vacuum Tube Amplifier

Otona no Kagaku (Science for Adults) Product Version Tube Amplifier Instructions for Assembly and Operating Parts List

PARTS A PARTS A PARTS D PARTS D A1: Horns (top) (2) D1: Vacuum tubes A2: Horns (bottom) (2) A1 A2 A3 D1 D1 D2 D2 (1B2/blue) (2) A3: Partition plates (2) D2: Vacuum tubes A4: Speakers (2) (2P3/yellow) (2) D3: box cover D4: Output trans- former covers (2) D5: Volume knob

A1 A2 A3 D3 D4 D4 D5

A4 A4 PARTS E E2 E2 PARTS E E1: Support posts (2) E1 E2: Tripods (2)

PARTS B PARTS B E1 B1: Main unit B2: Printed circuit B1 B2 board

PARTS F PARTS F F1: Audio cable F1

PARTS C PARTS C C3 C1: Battery contacts (negative) (2) C1 C1 C2 C2 C2: Battery contacts TOOL&PARTS 3 TOOL&PARTS (positive) (2) 1: Screw C3: Back cover 1 2 2: Washer head screw C4: Rubber pads (4) 3: Screwdriver C4 C4 C4 C4 4 4: Pin straightener CAUTION: The kit may contain more screws, NOTE: The actual shapes of some parts may differ from the illustrations above. etc. than actually required, for use as spares. 2 3 Before Assembling the Kit How to identify a vacuum tube 1. About the vacuum tube If the printed characters A. The vacuum tubes in this kit were manufactured in China, are too faint to read, go by the color on the bottom of more than 30 years ago. They may have some scratches and the vacuum tube. smudges. However, they will perform well. (We do not accept returns of scratched or dirty vacuum tubes. Tubes that do not work will be exchanged.) CAUTION * Please read the following instructions before assembling this kit. B. There are two types of vacuum tubes. If it is too dirty to tell what type it is, you can identify it by the color on the  The vacuum tubes are made of glass. Take necessary caution when handling them. There is a risk of injury. Yellow Blue  For best performance, the fixtures are made of thin metals. Take necessary caution when handling them. There is a bottom of each vacuum tube. risk of injury. C. Vacuum tubes are fragile. Please handle them carefully.  The tip of a vacuum tube is sharply pointed. Take necessary caution when handling them. There is a risk of injury.  There are small parts included in the kit. Be careful not to swallow them. There is a risk of suffocation.

Two D dry cells are used. Incorrect use of the batteries may cause the generation of heat, explosions or liquid leakage. The following precautions should be taken.  To avoid heater problems, do not use Oxyride batteries.  Do not use NiCd and other rechargeable batteries. With such batteries, the amplification process may not operate properly.  Ensure that the positive and negative terminals of the batteries are aligned correctly.  If liquid that leaked from batteries gets into your eyes, rinse it well with plenty of water and consult a doctor immediately. If liquid leaks onto your skin or clothes, immediately wash it off.  When the amplifier is not used for a long time, have the batteries removed.

 Please read the instructions and cautions thoroughly before use.  For your safety, be sure to follow the instructions in this manual. In addition, do not use any parts that have become damaged or deformed during use.  Store the kit in a location out of the reach of small children. How to use driver (+). ● materials used in this kit 2. Using the supplied tool Main unit, cover, horn, support post, screwdriver handle, etc.: ABS * Vinyl chloride resin is used in the lead cover. ●Screwdriver (Phillips) * Please dispose of this product in accordance with local regulations.

回す The screwdriver is used when tightening a screw. * The screws in this kit are “tapping screws” that carve grooves into the material as they are inserted.

3.Other required items Two D alkaline batteries * NiCd rechargeable batteries or Oxyride batteries cannot be used instead of D alkaline batteries. * The “Speaker experiment” and “Circuit modification experiment” require other items (see pages 12 and 14.) * Note: In some cases, the shape and the length of materials may differ somewhat from the photographs and illustrations provided in this manual. 4 5 1 Assembling the Horns 2 Assembling the Main Unit Parts to be used PARTS A Parts to be used PARTS B A1: Horns (top) (2) A2: Horns (bottom) (2) A3: Partition plates (2) A4: Speakers (2) B1: Main unit B2: Screws (8)

Figure-(3) Align the RCA terminal on the (3) Install the B2 printed circuit Screws (4) B2 printed circuit board with the volume. While using board into the B1 main unit. caution not to break the pilot light, install the B2 printed circuit board into the B1 main B1: Main unit Figure-(1) unit. Insert an A3 partition (1) Assemble two sets of horns. How to install the B2 plate between an A1 printed circuit board Screw horn (top) and an A2 Align the RCA terminal, the horn (bottom). volume, and the pilot light with Screw When doing so, insert A1: the holes on the B1 main unit, B2: Printed Horn and then fit it into the B1 main the pins on the unit. circuit board partition plate into the (top) A1 horn (top) and the A2 horn (bottom). Pin RCA terminal Make two sets. A3: Volume After that, secure them Partition RCA terminal with screws. plate A2: CAUTION Horn B2: Printed circuit board While using caution (bottom) not to crush the Figure-(4) pilot light, push it After installing the B2 printed in so that its head sticks out here. Figure-(2) circuit board into the B1 main Attach the A4 speakers (2) Attach the A4 speakers to the horns. unit, flip it upside down and to the two sets of horns secure it with eight screws on assembled in A1: Horn (top) A4: Speaker the back side. (4) Attach the B2 printed circuit Figure-(1). How to tighten the screw board to the B1 main unit. Screw After temporarily tightening Screw all the screws, gradually ネジ provide additional tightening Screw diagonally.

Insert it all the way in. Screw A2: Horn (bottom) Screw

6 7 3 Mounting the Battery Contacts 4 Setting the Vacuum Tubes Parts to be used PARTS C Parts to be used PARTS D C1: Battery contacts C2: Battery contacts C3: Back cover C4: Rubber pads (4)） D1 : Vacuum tubes] D2 : Vacuum tubes D3 : Battery box cover D4 : Output (negative) (2) (positive) (2) (blue) (2) (yellow) (2) covers (2)

Washer head screws (7)

D5 Volume Pin straightener Pin straightener knob Figure-(5) Figure-(7) Mount the C1 and C2 battery (5) Attach the C1 and C2 battery contacts contacts on the battery box. Attach the D3 battery box (7) Attach the D3 battery box cover, Push them in using the back of to the battery box on the B1 main unit. cover, D4 output transformer D4 output transformer cover, and the pin straightener so that it cover, and D5 volume knob to D5 volume knob. C1: Battery contacts C2 will not protrude from the edge. (negative) the B1 main unit. : Battery contacts (positive) D3 : Battery box cover Pin straightener D5 volume knob mounting position D4 Output transformer D4: Output : Main unit cover B1 transformer cover B1 : Main unit

Washer This position Note the attachment position. head screws Mount the volume knob D5 Volume knob After mounting the battery contacts, as shown in the figure. flip the B1 main unit upside down. Washer head screws (8) Using the pin straightener, set the Bend and crease the C1 and C2 Figure-(8) battery contacts that have vacuum tube pins perpendicular. B2: Printed Vertically insert the pins of protruded from the back, along the circuit board the vacuum tubes into the Set it vertical B2 printed circuit board, and secure holes on the pin straightener. Pin straightener them with washer head screws. B1 : If pins are bent, straighten Main unit How to attach battery contacts them. (Use caution so that the pins are not broken.) Washer head screw (6) Attach the C3 back cover Vacuum tube to the B1 main unit. Figure-(9) While carefully noting the (9) While noting the insertion positions, Washer head screws positions into which they are C4 : Rubber pad inserted, set the D1 and D2 set the D1 and D2 vacuum tubes. C4 : Rubber pad Washer vacuum tubes on the B1 main unit. D2 : Vacuum tube D1 : Vacuum tubes head screws (2P3/yellow) How to identify (1B2/blue) Bend Washer head a vacuum tube screws : Vacuum tube If the printed characters are D2 (2P3/yellow) C4 : Rubber pad too faint to read, go by the color C3 : Back cover on the bottom of the vacuum Enlarged view tube. Figure-(6) Attach the C4 rubber pads to the four corners of the C3 back cover. After that, using three washer B1 : Main unit head screws, attach the C3 back Yellow 2P3 1B2 cover to the B1 main unit. Blue B1 : Main unit 8 9 5 Assembling and Connecting the Speakers 6 Listening to Music Parts to be used PARTS E Parts to be used (12) Set two D alkaline batteries E1 : Support posts (2) E2 : Tripods (2) PARTS F (sold separately). F1 : Audio cable D alkaline batteries (not included)

B1 : Main unit

D alkaline batteries (2) (sold separately)

Figure-(10) * The speakers are not shown in the illustration. Set the E1 support post (10) Mount the speakers onto the base on the E2 tripod to (make two sets). Figure-(12) make a base. Set two D alkaline batteries (13) Connect a device, etc., Then, mount the The speaker assembled E1 : in Figure-(2) (sold separately) in the to the Vacuum Tube Amplifie speakers that were Support battery box of the B1 main assembled in Figure-(2) post unit. Low High to the base. Figure-(13) Vacuum Tube Insert With the F1 audio cable, Amplifier connect a digital audio device, etc., to the Vacuum OFF E2 : Tripod Tube Amplifier.

Left RCA Right (red) Figure-(14) (white) terminal Turn on the digital audio device, etc. * For how to turn on the digital audio, F1 Audio cable etc., see the instructions that are * Connect the cable to Figure-(11) supplied with the equipment. Digital the RCA terminals (11) Connect the speakers to the back of audio Connect the speaker while matching colors. the B1 main unit. Turn on the (the D5 device and the like to the speaker volume knob) for the terminals on the back of Vacuum Tube Amplifier, the B1 main unit by (14) Adjust the sound volume with the and rotate the knob to matching the red and D5 volume knob. adjust the sound volume. black colors. * The volume can also be adjusted on Speaker the digital audio device side (adjust it CAUTION: How to connect while listening to the sound). The glow of the speaker wires the pilot light Securely press the terminal The speakers can be changes with button. Insert the detached from the tripod and the sound. conducting parts on the tips B1 : Main unit of the speaker wires into the attached to the B1 main unit. (rear) open space. B1 Digital audio : Main unit device and the like

Speaker Tripod Speaker wire (black) D5 Terminal Speaker wire (red) : Volume knob button 10 11 motion of the vibrating plate, and this reduces 7 Experimenting with the Speaker Sound ★ Explanation ★ the sound volume. A. On the backside pipe experiment (Fig. 3) Cotton or other stuff What causes the change in sound when pipes A. Backside pipe experiment are inserted into the back of the speaker? The speaker generates sound when the Required items ● vibrating plate (the corn, see page 19) vibrates Cardboard Ruler (1) Make backside pipes with a piece ・ ・ ・ the surrounding air. The sound, irrespective of Cellophane tape ・Scissors of cardboard. Pipe A the type of the sound source, is emitted from the rear of the speaker as well as the front side Figure-(1) Approx. With a ruler, measure the 4.4 cm of it. For this reason, if the speaker is operated as B. On the characteristics sizes shown in the figure. Approx. a single unit, the sound from the back travels to experiment (magic box) Pipe B Using scissors, cut a piece of 15 cm Approx. the front side and becomes mixed (Fig. 1), The frequency characteristics experiment refers cardboard. Roll up the Fix it with tape. 4.4 cm creating a flat, monotone sound. In particular, in or less to an “experiment for verifying how the output cardboard to create Pipe A the low-pitched sound, the sound from the front changes when the frequency is varied while and Pipe B (secure them Approx. side is canceled out by the sound from the back 20 cm. * So that this can fit in Pipe A. holding the input fixed.” By attaching with cellophane tapes). side. straws with varying lengths to the holes on the (2) Insert the backside pipes into the back can be improved by reducing the back of the speaker, you can vary the antiphase amount of sound traveling from the back side. Figure-(2) of the speaker. Change the length and frequency (in this case, it means the vibration of By reducing the area in which the backside is the air in the back) (Fig. 4). With your own ears, Set the Pipe A that was check to see how the sound changes. open, the amount of sound propagated can be assembled in Figure-(1) in check how the sound emanating from the minimized. Therefore, in this backside pipe speaker changes as the number and the length the Pipe B, and insert it into experiment, the backside is elongated using the the back of the speaker. Slide of the straws attached are changed. You can feel pipe to reduce the amount of open area on the change in sound quality. the backside pipe to change Pipe B backside (Fig. 2), and you check to see how the its length, and check any Pipe A sound actually changes. change in sound that occurs. Straw (resonating pipe) B. Frequency characteristics (Fig. 1) experiment (magic voice)

●Required items (Fig. 2) ・Straws (approx. 6 mm (1) Cut the straws (approx. 6 mm diameter) Straw (resonating pipe) diameter) Scissors ・ in appropriate lengths. The resonating frequency Figure-(1) is enhanced in the back. (Fig. 4) Cut the straws into varying lengths. Changing the length of a pipe causes the pipe Figure-(2) to “vibrate,” or “resonate.” As a result, the Insert the cut straws into vibrating plate also vibrates extensively in a the eight holes on the back (2) Stick the straws to the back of the specific frequency in tune with the length. At of the speaker. Insert straws speaker. Check to see how the the same time, the volume of the specific of different lengths, and also sound varies. frequency that is emitted forward increases. change the number of How does the sound change if the open state in straws; check the resulting the backside is blocked? It can be ascertained variation in sound. that the volume diminishes if the ends of the backside pipes are plugged with cotton or other materials (Fig. 3). The reason is that while the * For an explanation of “frequency characteristics,” see sound propagation is inhibited and sound page 20. quality is improved, the closed space impairs the 12 13 8 Circuit Modification Experiment ★ Explanation ★

A. On modification toward energy-saving mode * and circuit diagrams Removing the solder in the solder shorts (parts A. Experiment on modification connected with solder) in A and A’ from the printed circuit board reduces output to some toward energy-saving mode extent, but it turns the Vacuum Tube Amplifier Pentode into a unit with an energy-saving mode (the Required items Remove solder from spots A and A’. batteries will last two times longer). ・Soldering iron・Solder・ The reason is that only one of the two heaters Absorbing wire will be used. (In the unlikely event that the The condition of the board with the solder removed heater on the operating side is blown, the remaining heater can be restored to its original Remove the C3 back cover condition by resodering the open in A.) from the Vacuum Tube Amplifier. Take out the B2 A A' B. On modification from a pentode to a triode Triode printed circuit board. Setting By removing the solder at B and B’ from the the B2 printed circuit board circuit board and jumpering two locations, C and Remove the solder. Remove the solder. upside down, from the printed D, and C’ and D’ with lead wires (lead wires are parts, remove the solder in * How to remove solder not supplied; they must be procured on your two spots, A and A’, as shown own), you can modify the circuit from a pentode in the figure. After removing to a triode. the solder, re-assemble the The triode, which is a classical circuit, is lower in Vacuum Tube Amplifier. sound volume than the pentode, but it is said to Although the output will be produce a softer and smoother sound. (The somewhat lower, the resulting Put the tip of the soldering The solder is absorbed “2P3” used for amplification is a pentode energy-saving mode makes iron on the absorbing wire by the absorbing wire. tube, which can also be used in a triode.) and hold it. the batteries last longer.

B. Experiment on modification *CAUTION: Any circuit modification using solder should be performed at from a pentode to a triode your own risk. Some solder contains lead, so be careful when handling it.

Required items ・Soldering iron・Solder・ Remove solder from B and B’. Then Main specifications for this kit Absorbing wire・Lead wire connect C to D, and C’ to D’ with lead wires. ● Accessories Remove the C3 back cover from ● Output: 100 mW/ch the Vacuum Tube Amplifier. ● Vacuum tube used (directly-heated, ・Multicellular horn speaker: 250 mW/8 Ω, battery tube): amplification: 1B2 full-range style x 2 Take out the B2 printed circuit A A' board. Setting the B2 printed x 2 / Power amplification: 2P3 x 2 ・Audio cable: RCA pin plug x 2 and stereo circuit board upside down, ● Input terminal: RCA terminal mini-plug from the printed parts, remove Connect ● Input sensitivity (): 1 the solder in two spots, B and Connect with a Vp-p/100 k with a lead lead wire. B’, as shown in the figure. wire. ● Load (output) impedance: 8 to 16 D C' Next, connect C to D, and C’ to C D' ● Frequency characteristics: 100 to 10 D’, as shown in the figure, with B B' kHz (+0, -6 dB) lead wires. When finished with ● : 5% maximum (1 kHz) this operation, re-assemble the Remove Remove the solder. the solder. Vacuum Tube Amplifier. This turns the pentode circuit into a classical triode.

14 15 In subsequent years, AC power made its way which means that there is very little chance ★ About the Vacuum Tube Amplifier ★ to homes to provide a . It was for accidents resulting from electric shock. found, however, that heating a directly-heated These tubes, as in the case of the supplied kit, filament with AC power caused deterioration are well-suited for use in hand-made kits. filament and a positive voltage is applied to it, in sound quality. In order to prevent this 1 What is an “amp”? the emitted are adsorbed onto the phenomenon, the indirectly-heated tube was 2. They run on DC power metal plate, causing a current to flow from the created in 1926. In this device, the heater The ability to run on DC power provides a The “amp” in the term “Vacuum Tube Amp” is metal plate to the filament (Fig. 1). (corresponding to the filament in a directly- significant advantage. In the case of AC power, an abbreviation for “amplifier,” and it means heated tube) is wrapped in an material electrical vibrations are unavoidable (when changing the of an input electrical * How a tube works and heated, causing the emission of electrons. turned on, the indirectly-heated tube emits a signal and producing an electrical signal with When heated, the heater becomes so red that it booming sound, which is a type of vibration), a larger amplitude. The process is referred to begins to emit light (Fig. 2). and this affects sound quality. For audio Metal plate as “amplification.” Current equipment, batteries are ideal power supplies. If an electrical signal supplied from an * How the directly-heated and the external audio device, such as a digital audio Electrons indirectly-heated tubes work 3. They are quick acting unit, is simply fed as is to a speaker, it is not Load Indirectly-heated tubes that run on AC power possible to produce sound with the same require about 15 seconds until the heater Directly heated tube Indirectly heated tube volume and quality in an audible form from + warms up and the tube begins to operate. Filament P the speaker. Therefore, an electrical process, P Unlike the indirectly-heated tube, because it such as “amplification,” is needed. For this − G G does not require the heating of the filament, reason, a piece of equipment called an “amp” + − Vacuum tube glass the battery tube begins to operate as soon as it would be required. As a consequence, the most (Fig. 1) is turned on. critical part of an audio system is the K F amplifier. In the case of this kit, it is a vacuum In search of maximum efficiency H tube. In 1912, American electrical engineer Lee De 4 When compared with -produced Forest conceived the idea of regulating the P : Plate K : Battery tubes also have some disadvantages: G : Grid H : Heater amplification, amplification by a vacuum tube current flowing between the filament and the the power supplied from the battery is F : Filament is said to produce a “softer sound.” metal plate by placing lattice-like necessarily low compared with AC power, and (grid) between the metal plate and the (Fig. 2) this places a limit on performance. In this What is a “vacuum tube”? filament and by applying a negative voltage, Advantages of the battery tube respect, the supplied kit is designed using 2 the same as the electrons, to it. This is the 3 innovation for drawing out the maximum The origins of the vacuum tube trace back to birth of the triode. When this device is used, The popular conception that a vacuum tube performance inherent in the battery tube. no less than . Edison, who the current changes significantly in reaction to “glows in red” is a characteristic of the 1. Independently-Developed Output discovered the electric bulb, in conducting a small change in voltage applied to the grid, indirectly-heated tube which became the Transformer further research, found that when a metal is and in this manner, electrical can be mainstream during the 1930s and in A transformer is an heated to high temperatures in a vacuum, amplified. After a series of refinements that subsequent years. Since this kit consists of made by combining two coils. A coil is an electrons are emitted from its surface, and he were made in the succeeding years, the device directly-heated type battery tubes, in order to electronic component in which a conducting took out a patent in 1885 for this discovery. achieved a remarkable development in the minimize power consumption and provide a wire is wound in a helical form. Applying a This phenomenon is dubbed the “Edison effect” form of an amplifier. high-efficiency amplification function, these current to the coil produces a magnetic field or the “ phenomenon.” In the 1910s, the vacuum tube was a directly- tubes glow slightly, but not as much as around it. The transformer generates a voltage In 1904, British engineer J. A. Fleming created heated tube in which electrons are directly indirectly-heated tubes do. from the magnetic field produced by the coil a unit that can change the voltage through the emitted from the filament. In those times, AC Battery tubes offer several advantages: itself when the applied current is varied application of the Edison effect. The result is a power was not available in ordinary homes. (electromagnetic induction). A transformer is “vacuum tube” (diode). Therefore, it is supposed that batteries (dry 1. They are safe an electronic component that changes voltage Heating the filament in an electric bulb by cells and storage batteries for cars, that is, car Because they run on dry or storage batteries, due to the number of windings of two coils causes the emission of electrons by batteries) were used as a power source. In that so they basically have an energy-saving being different. the thermionic emission phenomenon. In era, directly-heated type battery tubes were design. Compared with AC power, these The output transformer is a key component addition, when a metal plate is placed near the standard. batteries are low in both current and voltage, 16 17 that determines the sound quality produced progressing order of electrical processing. Steps for the processing of by the amplifier. The impedance (a concept Consequently, the RCA terminal is located in electrical signals similar to “resistance” in – see the front, and the speaker terminals in the Output transformer page 21) of the signal amplified by the back. If these components are placed in vacuum tube must be reduced to the proximity to one another, electrical coupling (4) Speaker impedance used in the speakers. For the occurs, with an attendant decrease in sound (5) terminals (1) RCA terminal Speaker⑥ faithful reproduction of sound quality, the quality. (3) waveform should remain the same. Critical elements in achieving such a performance are Electrical signals are processed as follows Volume the quality of the core material and the (Fig. 4): (2) Backside stacking thickness (a thickness attained by stacking slim core materials – the greater the (1) RCA terminal Electrical signal (sound 10KΩ 8Ω 8Ω thickness, the higher the performance level of source) is input from an external audio device. the transformer). (Fig. 3) (2) Volume Adjusts the overall volume of the Front side * Shape of the core material used in an input signal. (Fig. 4) output transformer (3) Vacuum tube (1B2) Amplifies the voltage of the input signal. (4) Vacuum tube (2P3) Amplifies the power (= voltage x current) of the input signal. then releasing it in a burst – a technique that * How a speaker unit works (5) Output transformer Matches the was used in an early gramophone sound box). amplified signal to the speaker impedance. (Fig. 6) * Enlarged view of the speaker unit (6) Speaker terminals Output the amplified The shape of the horn incorporates the Cone (MylarCone cone; (Mylar it vibrates cone; it and vibrates and produces sound)produces sound) electrical signal to the speaker. classical “cellular type” (where a horn is (Fig. 3) partitioned into small compartments so that Speakers that fully utilize the individual high range are produced Magnet Magnet (neodymium(neodymium class magnet) class magnet) 5 output with great clarity). This method was originally Moves Moves Stacking As a vacuum tube amplifier, the main unit is developed for middle and high range sounds. Coil Coil (Fig. 5) thickness a self-contained unit. However, to listen to However, since the supplied kit uses full-range The supplied kit contains an irregular EE core speakers, the low range sound can also be actual sound, speakers are required. Believing Magnet Magnet Air chamber type transformer. The code “EE” is associated that speakers cannot be omitted from the kit, covered. You can enjoy a sound different from Horn HornAir chamber with the shape of the core material. The we decided to include speaker units that are high-. Stereo wiresStereo wires supplied transformer was independently capable of drawing out maximum sound from developed by Gakken, in search of an ideal a low-power input in the kit. output transformer. Also, a special steel plate, A speaker is comprised of two elements: an “ steel plate” is used in the core integrated cone (vibrating plate) and coil, and material. independent magnets (Fig. 5). Each of the speakers supplied with this kit is equipped Cone + coilCone + coil (Fig. 6) 2. Appropriate arrangement of electronic with a size 40-diameter mylar cone (plastic components cone) and a coil, to which a neodymium class An amp always has input and output sections. magnet is attached. As such, they are “full- In the supplied kit, the RCA terminal into range speakers” (with emphasis on the middle which a signal from an external audio device range while maintaining low and high range is fed corresponds to an input part, and the characteristics). An air chamber is provided speaker terminal corresponds to an output on the front side, producing an increased part. In arranging the electronic components, sound volume and delivering an improved we designed the circuit board so that the sound quality through an air suspension effect input parts are located in the front and the (an effect that physically changes the sound output parts are in the back (rear), in volume and quality by compressing air and 18 19 and 6 dB, 2 times greater. Output (dB) Glossary of Audio Terms 0dB ★ ★ ● Crosstalk The term refers to the condition in which the right ● Stereo amp the value, the greater the quality of the amp. In -6dB and left signals are mixed. Even when they are An amplifier that consists of right and left units. The practice, the limit is a few percentage points. completely separated on a circuit diagram, in an separate right and left sound sources create a Normally, sine waves (neat waves that are generated actual circuit, right and left signals often become stereophonic effect. based upon a mathematical formula) at 400 or 1000 mixed due to ground loop and electromagnetic Hz are input, and the output waves are measured coupling. Normally crosstalk is expressed in dB ● with a distortion factor meter. The distortion factor is (), such that the greater the number, the 100 1k 10k A current that flows in alternately in opposite an index for the extent to which signal is faithfully higher the performance. For the measurement Frequency (Hz) directions at a fixed cycle. amplified. method, with a sine wave input, the ratio between a state matching the rated output and the value of ● Power supply frequency ● Amplifier output no-signal is measured. For example, a crosstalk level ● Meaning of “Speakers: 250 mW/8 Ω” The electricity supplied to homes is an AC current, in In this kit, the expression “100 mW/ch” means a of 46 dB means that signals are mixed in a 1/200 (see page15, “Main specifications for this kit”) which the direction of current flow changes every capacity to output 100 mW per channel. Normally ratio. The term refers to a maximum input of 250 mW; no 0.02 second. The length of time for this repeated this indicates the maximum output. However, in the greater signal input may be applied. The 8 cycle, in which the amount of time that cycle field of , it often indicates an represents the load impedance, meaning that the ● Impedance completes itself, from the beginning to the end, is output level with a 10% distortion. In terms of a The term refers to an AC resistance level. In audio speaker can be connected to an amp with a referred to as a period. The number of periods (the measurement method, the output voltage is devices, the term normally means a resistance at 400 maximum impedance of 8 Ω. number of times cycles repeated) per second is measured with a rated input of 400 or 1000 Hz. or 1000 Hz. Because the output from a vacuum tube called the power supply frequency (50 Hz in Eastern Normally, a fixed resistance (8 Ω) is used as a load. Japan, and 60 Hz in Western Japan). has a value, directly driving an 8-Ω speaker produces a large drop in voltage, and ● Rated input inhibits output. An attendant increase in distortion ● Audio band The term refers to the voltage of input signal (sound could also reduce sound quality. In the supplied kit, This refers to the frequency band that is audible to source). Normally, the voltage is expressed as a an output transformer is provided between the humans. Normally it is 20 Hz to 20 kHz (20,000 Hz). A potential difference between the peak and the vacuum tubes and the speakers to achieve frequency band below 20 Hz is called the ultra low trough of a wave, often based on 1 V. Because the . frequency; the frequency above 20 kHz is called the rated output is used as a reference in the , both of which are beyond the measurement of a distortion factor or the S/N ratio, ● Output transformer ability of humans to hear. the input signal level is lowered. The term refers to an electronic component in which two coils are used in combination. The functions of ● Frequency characteristics ● S/N ratio an output transformer used in an amplifier are to The term refers to the degree to which a frequency The term refers to a signal to ratio, and it provide I/O impedance matching, to perform low- range of interest is amplified. In the case of an audio represents the percentage of noise that is generated distortion transformation, and to perform the amp, the extent to which degree of amplification in the amplification or impedance transformation necessary and sufficient power transmission. The key declines is indicated in terms of the range of the process. This is usually expressed in dB (decibel); the is to wind a thick winding wire around a highly frequency to be amplified. larger the number, the better the performance. For magnetic core a large number of times. The supplied example, an amp with an S/N ratio of 60 dB kit includes a transformer with a 10 kΩ : 8 Ω output ● Audio amp produces a noise component that is only 1/1000 capacity. A device that amplifies a weak signal to a high with respect to the signal. For the measurement signal. An ideal audio amp is the one that faithfully method, with a sine wave input, the ratio between a ● Meaning of “Frequency characteristics: 100 to 10 amplifies a given sound source in a flat manner (= state matching the rated output and the value of kHz (+0, -6 dB)” (see page15, “Main specifications for favorable frequency characteristics), ranging from no-signal is measured. the low range sound to the high range sound. this kit”) It means an “output decrease of 0 to -6 dB at 100 Hz ● dB (decibel) or 10 kHz (“-6 dB” indicates a 1/2 decrease in ● Distortion factor The term refers to a unit of measure, expressed output).” When the input and output signals are not similar in logarithmically, that represents the magnitude of waveform, the characteristic is referred to as a voltage or power. In a normal comparison of “distortion.” The distortion factor is a numerical value , 20 = 20log10, and 20 dB means 10 that indicates the extent of distortion: the smaller times greater. 40 dB would mean 100 times greater;

20 21 Vacuum Tube Amplifier

Q: No sound is produced. A: Check the direction of the batteries, whether parts are in contact, and whether vacuum tubes have

8 Ω /0.5 w speaker not been plugged in wrong. Q: The LED on the pilot light does not light up. A: Check the contact of the batteries. A loose screw on the printed circuit board can cause a contact failure. If this is the case, retighten it. Also, if a vacuum tube is plugged in incorrectly, the LED on the pilot light can dim. Q: What is the function of the LED on the pilot lamp? A: It is used to ensure an adequate bias voltage for the vacuum tube (2P3) (approx. 1.5V). T1 Q: The vacuum tubes don't get bright. A: In this kit, in order to conserve battery power, only a minimum necessary current is applied to the vacuum tubes. Therefore, they glow to an extent that that they are barely visible in a dark place.

C4 Q: The speakers .

1000P A: Sound from the speakers may be feeding back to the heaters on the vacuum tubes, etc., creating a (3)

C5 feedback loop. Turn the power supply on again. The shock generated when the switch is turned on (7)

(6) can cause feedback. Turn the switch knob gently. 470µF (5)

(2) Q: I want to test the vacuum tubes. (1) 2P3 A: Use the resistance range (a range of ×10 Ω or more) to check for blown heaters. Never (4) measure with a low range (×1 Ω). This could break the vacuum tube heater.

1M Q: What are the model numbers for equivalents of the vacuum tubes? R4 C3 A: 1B2 corresponds to 1S5; 2P3 to 3A4. Q: By mistake, I inserted a vacuum tube incorrectly. 47µF R3 270 D1 LED A: This will not break it, but it should be inserted correctly. Note that removing it could bend the pins. If

C2 it does, straighten them with the provided pin straightener. Power supply unit 0.01µF Q: How long will the batteries last? A: At a usage rate of one hour per day, the batteries will last for approximately 20 days. Q: What are the signs of a dying battery? A: Volume gets steadily weaker. R2 100K ㈬ ㈯ The circuit for the R channel is identical to the one for L channel. ㈭ ㈰ 1B2 ㈫ R1 510K 0.01µF C1 VR1 500K S1 ON/OFF 1.5 V battery L-IN R-IN Vacuum Tube Amplifier Circuit Diagram

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