Line Introduction
1. Input voltage amplifier stage
SRPP circuit (shunt regulator known as push-pull circuit) is a circuit respected by the circuit having a small distortion, low noise, wide frequency response characteristics, is now one of the best line circuit common tube amplifier.
Circuit shown in Figure. VT1, VT2 DC path connected in series. VT1 constitutes a normal triode ambigumeric amplifier, VTR2 constitutes a cathode output, and VT2 is VT2 is a high resistance load with current negative feedback. Audio signal (3) from the input pin 6N3, VT1 after amplification from the first common cathode output pin ④ into VT2 cathode follower configuration, and then outputs the VT2⑧ pin. Into the post-stage circuit. VT2 is in the form of a cathode output, and its voltage amplification is close to 1, so the voltage amplification of the input stage SRPP circuit is mainly dependent on VT1. Meanwhile, VTl, VT2 AC path R4 (i.e., the power output stage of the gate resistor VT3) in terms of the equivalent load resistance of the input stage "in parallel", the common cathode tube opposite of the single amplifier internal resistance reduced by half, with a large load capacity In order to improve, easy and low-impedance load matching, and therefore sound quality has greatly improved. And because VT1, VT2 for R4 is a push-pull work load, the output current is doubled, the distortion is also reduced. AC bypass capacitor C1 is a cathode of VTl. R3 to avoid AC signal from the alternating current negative feedback to improve the magnification AC input stage, the input stage to improve the driving capability of VT3.
2.6V voltage drop on R3, as the gate bias voltage VT1 of negative, negative pressure than this modern digital audio output signal of large amplitude 1.5V, the non-linear portion avoiding a male 6N3 dynamic characteristic of the gate. The input stage of voltage amplification factor: A = u · R4 / (Ri / 2 + R4) = 35 · 360k / (5.8k / 2 + 360k) ≈35 times. 6N3 wherein u is an amplification factor, the value of 35; Ri is 6N3 resistance value of 5.8k.
2. The power output stage power transistor 6P3P standard connection, the control signal generated by a gate (pin ⑤) input, the screen grid (pin ④) directly connected to the power source + B1. This connection features are: high amplification efficiency. To achieve output characteristics table specified amplifier tube. Cathode resistance R6 is an output stage, the output stage of the gate in the negative pressure determined -20V. 6P3P screen voltage is 290V, the gate is negative -20V, screen flow of 50mA, for class A amplification, the output power of about 5 5W, satisfies the basic requirements of a typical home environment playback.
3. Power circuit
Power rectifying circuit using a conventional tube, CLC-π type filter tube amps while maintaining the traditional musical flavor, but also the whole harmony tone and balance.
Dual voltage 250V 523P via full-wave rectified output from the power transformer secondary, CLC-π 100Hz filter output via a unidirectional pulsating DC C6, L1, C7 composition obtained stable DC high voltage. Tube rectifier experience in the warm-up process without high pressure impact, with the protection of the tube, and this is especially important when used in astronomical tube amplifier circuit. The CLC-π-type filter mode is well filtered, and the power supply is low, which has great benefits to reducing noise and improving the whole machine. R7, R8 is to protect C6. R9 is a high pressure discharge resistance of the high resistance against voltage surges peak pulse power tube output transformer and high voltage start-up.
Output transformer production
Output transformers are important components of the electronic pipe power discharge circuit. If the conditions are not met made, buy products can be constructed. Specific parameters of the machine shown in Figure 2 with the output transformer. The iron core is 22 × 33 cold-rolled silicon steel sheet, the initial total is 3300 laps, divided into two layers, the line diameter is O 18mm; the secondary has a total of 172 laps, which is divided into three layers, and the wire diameter is 0.82 mm. The air gap left by EI silicon steel sheet is O. 08mm, the maximum operating current is 70mA, the power is 8.5W.
Production and debugging
This machine is simple, less components are small, can be used to weld, and make debugging simple, high success rate.
Can be prepared first welding power supply and the filament portion prior to welding after a normal power amplifying circuit is to be noted that, when the no-load, higher voltage, the capacitor voltage must meet the requirements of FIG. 1. FIG marked several test point voltage is the voltage measured when I produced, can be produced as a reference, when the grid voltage fluctuation is not, the test value should be close to the above, mention this success. R2, R3, R4, R6 may be changed machine operation state, the production process to attract attention, in particular R2, R3 error can not be too large, otherwise vTl④ feet may not be equal to the DC voltage + B2 half voltage. The machine measured output power of about 5.5W, pure and mellow sound, good control of the speaker, and the rich tube taste, music lifestyle.
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