A amplifier more and more attention. One reason for the CPI amplifier crossover distortion does not exist, does not produce unpleasant odd harmonics, which is the key to the pure sound quality. The second is A amplifier has been working in the best condition, will not have that kind of switch B amplified distortion. It is characterized by a negative feedback loop to cancel a large order to avoid transient intermodulation distortion, the dynamic index increased substantially.
    The machine design specifically for the study, no fair without, but only to its excellent sound. A single-tube by tube amplifier, both out of consideration of quality, but also take into account the amateur production of push-pull tube amplifier matching problem difficult to solve. Although less efficient tube Pure Class A amplifier, but its power reserves, compared with the transistor amplifier can be as small as half. Research data show that there is pure A and B power For the same quality (referring to Pure Class A amplifier power does not exceed the rated value), the latter shall have the power 9 times the reserves of the former. So, Pure Class A amplifier is the absolute efficiency may be worse, but the relative efficiency is almost the same.
    Gentle tube sound with one of the Confucian style, is the so-called moderation, coupled with its own unique classic tube tone and nostalgic, warm enough to study tremendous atmosphere. If the gall bladder, such as those Ming KT88, KT100, 845, etc., can be called ru, then the machine may be called small Confucianism, if you enter your study in such a small Confucianism, is equivalent to procure the one of your bosom friend, depression when he softly paragraph language to comfort you, happy to add to the fun when he was laughing, why not   
   This machine has the following characteristics:
Undistorted output power 2 ~ 5W;
Circuit is simple, no special components and some components are given maintenance experience;
The machine wide frequency response, low distortion, high and low tone control circuit with the circuit, easy to use.
Circuit Work
  Machine diagram in Figure 1. Only 2 per channel just sub. Amplification of the tone before and after the network is divided into two parts for the industry. The first part of the voltage amplification part of the latter part of the last class before the class and power amplifier. VE1, VE2 selection of high µ pipe 6N2, to improve the machine sensitivity. Voltage amplifier stage of the major technical indicators amplification and frequency distortion. 6N2 amplification factor of 97.5, enough to meet the local requirements. Using resistance-capacitance coupling, intermediate frequency amplification region the largest amplitude frequency and phase frequency characteristics are very flat. While the low frequency region and high frequencies in the law are to a certain decline. Usually necessary to raise the upper limit of the frequency decreases the value of R4, to extend lower frequency would have increased the value of C1. After repeated testing, the unit anode voltage amplifier stage load resistor value 150k, C1 with 0.1µF. Before the end of class is a typical resistance of a cathode self bias and negative feedback voltage amplifier leapfrog.

Use low-frequency power amplifier stage amplifier pentode 6P14, the tube in the audio industry in the "Shu-quality excellence" reputation, the cathode area, long life, especially the high transconductance of soil 1.3mA / V, sensitivity and power amplifier efficiency are high, is an excellent amplifier tube, the actual installed capacity of Love also confirmed this. VE3 the gate resistor R11 has a certain impact on the quality, frequency response to get better, this machine is smaller as 400kO. Pentode amplification factor of the main advantages of larger, as the amplifier, we can obtain a higher magnification. At the same time due to screen grid and suppressor grid of the double shielding effect, and its capacitance is very small cross-road, such as the 6P14 to less than 0.2pF, the small high frequency loss. Of course, compared with the transistor, pentode used as the amplifier, the distortion and noise to be larger. However, after listening to the machine to install the system clean natural sound, transparent and bright, did not hear the noise, which is the work of state of the CPI.
    Power supply is rectified by 5Z2P, and then after a p type LC filter circuit on the machine power. Including filament winding, the voltage amplifier stage and power amplifier stage should be independent around the system, to reduce interference.
Specific experience in the production
1. Component selection.
    Tube VE1, VE2 use "J" grade 6N2, 6N1 available direct substitution. VE3 choose Beijing Brand 6P14, with which the same tube model 6BQ5. The machine of resistors, capacitors, no special requirements quality, resistance to the ordinary carbon film resistors. I used an old tube radio resistance are all removed items. Just for the sake of stability of the circuit, the resistance of the power should be selected larger, I use 1 watt of power are standard. Capacitor C1, C4, C5, C6, C7 ordinary polypropylene capacitors are available, pressure can be in more than 400. C2, C8 as an ordinary high-voltage solution can withstand more than 350V. C9, C10 pressure should be greater than 400V, conditions should be given priority by TV electrolysis. C3 200pF mica capacitor selection.
    Power transformer power should be greater than 100W, the primary and secondary should be added to a shield between the groups independent of filament winding, winding the data shown in Figure 1. Power transformer core model uses a "GEIB-35", cross-sectional area greater than 35 × 47mm2. 5Z2P supply voltage of 5V, with F1.21mm enameled wire around the 24 turns, the current should be = 3A. 6P14 amplifier tube filament supply voltage is 6.3V, with F1.21mm around 30 turns enameled wire, in the center tap, that tap e, connected to the 6P14 cathode can improve the signal to noise ratio. Choke Figure L available CEIB-22 silicon steel sheet, thick stack of 22mm, enameled with F0.28mm turn around 2700. In order to choke does not produce direct current saturation, there should be gaps in the iron core to increase the reluctance. To this end, the core mode can be superimposed on the stack, leaving a gap of about 0.5mm, the gap at the stuffed insulation paper, circling through the current to 150mA.
    High and low quality output transformer big impact on sound quality, can be purchased finished audio output transformer, power is 5W, the primary impedance is 5 ~ 5.2kO, secondary output impedance of 4 ~ 16O, model "OPT-5-5".
    470kO potentiometer RP1 should be used double exponential sound special potentiometer. RP2, RP3 can be used more than ordinary power of 2W potentiometer. RP4 with about 100O 2W wirewound potentiometers.
2. Installation and commissioning.
    Readers can choose according to their own conditions for installation. I stand with the tube radio, using the original seat tube, transformer and terminal, very convenient to install. If the clean side, readers can be printed circuit board, the sale of output transformer power transformer, choke, tubes, and large electrolytic capacitors installed in the upper part of the base metal sheet, the printed circuit board mounted on the base inside, which can prevent the RC components due to temperature changes caused by reference. To prevent the interference signal into, shall take the necessary measures. Power transformers can be installed upright, with support from the bracket to make it some distance above the base to prevent leakage flux transformer into the circuit through the floor caused hum. Power transformer and choke line package package mutually perpendicular lines, and as far as possible away from the output transformer. VE1, VE2 should stay away from the power transformer. Electrolytic capacitor should be away from the power amplifier tube, in order to avoid overheating and dry roasted failure.
    Various parts of the wiring should be as short as possible, the alignment can not be chaotic, with a component level should be close to the tube, and to ensure that ground. Tube gate leads should be as short and to avoid parallel with the screen extremely lead. Anode circuit and gate circuit wiring and floor to leave a little bit, thus reducing the number of potential distribution capacity. Stranded wire filament is best to go up by the floor to reduce the filament caused hum. Bypass capacitors must be directly from the tube socket or connected to the bypass point level ground. Capacitor lug can not be too long, because they were bypassed in the current sea-AC, easy, and other line sensors, and a long wire itself has inductance, inductive reactance of the formation of high-frequency current, thus reducing the role of the bypass. Special attention should lead to VE1 gate metal shield, and that the shield near the gate to ground. Note that the above matter as long as carefully welded, installed the system correctly, you can burn in Love power, not need to make adjustments.
Experience of some components of alternative
    6N1 voltage amplification which can be used instead of, instead of down after the R4 100kO, R8 reduced to 100kO, R10 down to about 50kO. When using 6N15 instead of altered method as above. Power rectifier diodes available 6Z4 e-substitution. 6Z4 tube due to the largest single DC output current is only 75mA, it is applied after the use of two tubes in parallel, the circuit changes as shown in Figure 2.

Semiconductor diodes can also be substituted. Only a slight change in sound, changes the circuit shown in Figure

Low-frequency speaker unit is available YDS-2004-type 8 inches rubber side speakers, high-frequency module of the YDG-3-type 2.5-inch Small loudspeakers, through a simple capacitor divider, crossover chosen 3kHz, can be audio-specific capacitors capacitors polarity, such as CD94-    Error-free as long as the components, welding correct lyrics start to burn half an hour, if the circuit is stable, try to cancel the feedback resistor R13, this time more transparent sound quality.
    I've used Philips CD47l Mount Type CD drive as the source, direct refutation of this machine, push the front two speakers introduced into the sealed bookshelf speaker, listening in the study, it is lingering aftertaste. Lyrics dish first with the wind company of Germany in 1990, published in Granma, "Peter and the Wolf", numbered "DG429 396-2", by the Chamber Orchestra of Europe conductor Claudio Abbado performance, history provides narration. One person will be attracted into the opening into the story. Small speakers that sound clear and unique sense of immersive Yang, close your eyes and feel it is also involved in the deal with Peter and the Wolf. Set aside the history as vivid nature, focuses on the plot. Peter dignified distress was a tense atmosphere when people breathe mining, when the wolf is defeated by a warm bucket inspiring lively rhythms, music that people enjoy the art of infinite charm. Also by Jennifer Warner's "Lan Yu floor," Love, the local interpretation of the perfect human voice so full of Jennifer Warner magnetic embodied most perfectly charming voice, saxophone Paul Seoul Saxophone dance makes you confused intoxicated. Pure tone of the people matter to praise Tiandie also tan electricity to the tube is not the old Castle Peak.
    I have also made the DM62 with head deck plus front straight split machine, listen to folk music played with. {Mountain stream during a zither music "empty mood far, vulgarity, Evans could not help but cause Quan.