Author: Gu Tianshun
Since playing the 12-inch full-frequency unit called "poison speakers" on the Internet, it is fascinated by the sound of smooth and natural smooth and natural, and also deeply understands that the single-ended stage is really Full-frequency optimal partner. The author already has 3 single-ended levels of single-ended, 805, 300b and 2A3, which are all known to everyone, and there is a mouthful of sound, and its output power is 40W, 8W and 3.5W. Although their sound is different, they also have a characteristic, and the smaller the output power, the more the sound is slim, and the emotional feelings are more realistic. So I gervested a thought: another single-ended single-ended level of power.
I. Finding the bold one to mention the small power single-ended, many people will think of power tubes with some beam tubes such as 6p1, 6p14, 6V6, 6L6, 6p3, 6p6 and the five-pole triodes to do power, and I don't like this approach because the beam tube and the five todes are used with triode picks, and their linear never cannot be compared to the true triode. Once an accidental opportunity, the author found a good gallbladder that has been forgotten, it is the protagonist introduced herein - 6C19. 6C19 is a side heat-type high-power single triode, main use is to regulate power adjustment tubes and OTL amplifiers. Its characteristic curve, the pin arrangement is shown in Figure 1, and the main parameters are attached to the table. The 6C19 is 300Ω, the anode dissipation power is 11W, and its performance has nothing to do in the thumb. Since it is not fried by the market, the price is very cheap, it is cheaper to make people dare not dare I believe there is such a good voice performance. In fact, a gallbladder sound can be directly linked to its price. More importantly, the quality of the bold itself and whether it can use it. Figure 1 6C19 Characteristic curve and pin arrangement
Main parameters of Schedule 6C19
parameter
symbol
index
Filament voltage
UF
6.3V
Filament current
IF
1A
Internal resistance
Ri
300Ω
Transconductance
S
7.5mA / V
Maximum anode current
IMAX
140mA
Maximum anode dissipation power
Pmax
11w
II. Circuit principle The author is based on the 6C19 characteristics and has produced a small power single-ended post-end. The entire machine is shown in Figure 2. Figure 2 The schematic of the whole machine is good, and its work points are important to the choice of load impedance. The internal resistance of 6C19 is 300Ω, and the impedance of the output transformer is 1 ~ 1.5 kq is suitable. It is just that someone sells 5W / 2.5KΩ single-ended output transformer, and the power is appropriate, and the impedance is slightly large, but the impedance is a little more contributing to the low frequency performance, so I bought a pair. After actually use, the effect is good. Comprehensive 6C19 features and recommended working conditions, and finally its work point is 200V of the screen, and the anode quiescent current is 45mA. In order to improve the dynamic performance and low frequency control of 6C19, there is no common self-suction, but a fixed bias is used, and the negative pressure of the D1, D2 is rectified, and the C7 is filtered, and the negative pressure of approximately 250V is output. R10, DW1 is stable. After pressure, W2, and R11, the gate pressure required for 6C19 is supplied. In addition, after 6C19 uses a fixed bias, it can improve the utilization of the power supply. Since the negative pressure of 6C19 is as high as about -60V, that is, if the input sensitivity is set to 1V, the promotion level must have a gain of less than 60 times that allows 6C19 to achieve full power output, so the requirements for the promotion level are higher. . The conventional practice has the following: (1) A medium μ tube or low μ tube is used to amplify; (2) use high μ for primary magnification, usually use common yin and SRPP connection, common tubes are 6N9 and 12AX7 (3) Use high amplified five-pole to zoom in to zoom in; (4) adding a medium to medium μ tube to push the cattle (using its boost amplification) as a direct push. According to the pen, if you need to make a need for the first level, you will not use two levels, because of this, it will bring the increase in phase shift, the signal-to-noise ratio deterioration, and the circuit tendency is complex. Finally, the eyes were locked in this composite tube on 6f2. The 6f2 contains a high amplification five-pole and a triode, and the pin is arranged as shown in Figure 3. Figure 36f2 The pin arrangement signal is enlarged after the inner five of its inside, and the coupling capacitor C is driven 6C19 after the triode is buffered. Since the output of the five-pole output is high, directly push 6C19 distortion will be large, the high frequency characteristics are poor, the dynamic and low frequency control are also affected, so the first stage is added by the buffer level consisting of 6F2 internal triodes. The power supply portion uses a direct rectifier 5Z4 to rectify, and the CLC constitutes a π-shaped filter circuit. The 6f2 filaments of the two channels share a set of power supplies, supplied from the triple voltage regulator LM7806.
III. Components Choose 6C19 with common Beijing-choiore tubes, of course, can find the former Soviet Union or European production. Due to the low price of 6C19, there are several preparations when prepared, try to find two paired, and help the sound. 6f2 is easier to find a Shanghai card, its European model is ECF82, the US model is 6U8, if you can find it, you can compare the characteristics of your respective sounds, and use it. The power transformer B2 power is 150W is sufficient. Due to the large voltage windows, if the core window is accommodated, an independent filament transformer can be added. Coupled capacitor C4 has a greater impact on the tone of the whole machine. With some noble capacitors such as Jensen M-CAP, the effect is of course good, but the price is too expensive, and it is not corresponding to this unit. When the author is made, a 0.15uF / 400V CJ10 metal-based paper-free capacitor is in parallel with a 0.1 UF / 250V WiMA capacitor. The metallic paper dielectric is medium frequencies, and the WiMA capacitor is high frequency, and the tone is intertwined, and the length of addition is taken. At the same time, these two capacitances are low. The oil immersion capacitor increases the charm and music of the incense. This has become a consensus of enthusiasts, but it will affect the dynamic performance of the amplifier, and the oil immersion capacitance is large, and it is difficult to fix the oil. It is not appropriate to use, and make it a taste, it is used to taste, so the power supply part uses an oil immersion capacitor having a capacity of 7 UF. The potentiometer that controls the volume uses a common ALPS potentiometer. The power switch is originally seen in Noble's rotation, and it is characterized by good feel, high reliability, helpless price is too high. Later, it was unintentionally found that a target value of 500Ω with a switchgeneizer can be used to modify the rotary power switch, and the actual use is found, the hand feeling and reliability and NOBLE is not connected, the price is only 1 yuan / only, The price is extremely high.
IV. Making debugging we make a courage, not only requires a beautiful sound quality, the appearance cannot be ignored, because one audio equipment, its function is not only for us to enjoy music, but also a home decorated art, in Visually requires beautiful, generous, giving people a pleasing feeling. To this end, when making this coupling, the author adopted a symmetrical design, and its floor processing is shown in Figure 4. Figure 4 The bottom plate machining chassis is compressed by a stainless steel plate having a thickness of 0.5 mm. The size is 240mm wide, the depth is 320mm, the height is 50mm, and the two sides are sandwiched, the size is 340 mm × 60 mm, and the thickness is 15mm. The appearance photo after the whole machine is shown in Figure 5, and reference is made. The whole machine only sets all the signal input, so the panel knob is relatively simple, with a total of 2 knobs. One control volume, one controls the power switch. After all the components of the whole machine are welded, you can start debugging after the check is correct. This machine is very simple, just adjust W2, W3, so that the voltage of two 6C19 cathode resistance R8 is 0.37V can start audition.
V. Connecting the machine, although only a few hundred yuan of investment, the performance of its sound is unexpected. When expressing people, it is particularly clear, real and natural, and the emotional expression of the song is exhausted, and it is three points. Replay the string, such as two Hu, when the guzheng, the sweet voice, the energetic residual sound and the empty feel, make people like the drunk, want to stop. Of course, the output power of this machine is only 2W, and the vocals and strings are its good play, such as letting it replay the dynamic symphony and drums, it seems difficult.
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