Homemade gallstone hybrid Hi-Fi amplifier

The electronic tube amplifier has attracted generations of audio enthusiasts with its warm, soft, full and sweet sound. But it also has a fatal weakness: the output impedance is high, and an output transformer is required to match it with ordinary speakers. However, a good output transformer is very expensive, which often makes the majority of "audiophiles" stop. This may be one of the reasons why the popularity of electronic tube amplifiers is not as high as that of transistor amplifiers. But
what miracle will happen if electronic tubes are used in the input stage and transistors are used in the final output part? Let's try it.
Figure 1 is a hybrid amplifier designed by the author using domestic tube 6N11, which may serve as a starting point for the majority of "tube" amplifier enthusiasts. Figure 2 is the power supply circuit.
　

Figure 2 Power supply circuit

In line with the principle of simplicity, the input stage uses 6N11 to form a parallel adjustment push-pull amplifier circuit (i.e. SRPP form). This circuit was originally designed as a high-frequency input stage in the television field and was later used in the audio field. The distortion and dynamic range of this circuit are better than those of the triode Class A amplifier circuit. In particular, the amplification of signals above 7 kHz is better than that of triode amplification, which makes up for the defect that the high-frequency response of the tube amplifier is not easy to do well.
The power amplifier post-stage uses an OCL circuit, which consists of a pair of high-power tubes. The tube models are: MJ11032 and MJ11033, which are produced by MOTOROLA in the United States. Its BVeco is 120 V. The maximum output current is 50 A, the power dissipation is 300 w, and the characteristic frequency is 30 MHz.
Component selection: 6N11 uses products from Beijing Shuguang Factory, and can be directly replaced with 6DJ8, 6922, etc. Of course, it can also be replaced with 6N3, which has a warm tone and is only half the price of 6N11, but the speed is much slower. The error of the resistance of R3 and R4 should be controlled within 99.9%. The method is to measure the voltage value at point A to see if it is half of VB2. The coupling capacitor C1 is preferably a MKP capacitor with a withstand voltage greater than 450 V. It can also be replaced by a WIMA capacitor or a CBB starting capacitor in a washing machine. Except for the resistors specified, the rest are 1/4 W metal film resistors. MJ11032 and MJ11033 should be original American products, while the tubes printed with the word "MEXICO" sold on the market have poor performance.
If the filament is powered by AC, it will sound mellow, but the AC sound is difficult to handle. At this time, the filament can be grounded at one end to solve the problem.
Since the circuit of this power amplifier is simple, in order to complete it as soon as possible, the author uses scaffolding welding to connect all the connections, and the result is no background noise. In static state, no noise can be heard at a distance of 1 m from the speaker.
The overall impression after listening to it is: the tone is mellow and full, which makes people never get tired of listening to it. When using an ordinary CD player as the sound source, there is no "digital" sound at all, and the sound is natural and smooth.