Sea leap R-50 vacuum tube amplifiers are 70 brand-name products. With the rise of transistor amplifier, it gradually disappeared from the stage of history. In recent years, I collected several from flea markets, high-quality accessories, all the excitement about high quality products. Dianyuan power transformer can supply 250W power. Maximum output of 80W power 50W output transformers, primary impedance of 6. 9k/ω, secondary impedance 0--4---8-16--250/ohms, but with different impedance of the speakers connected, but also can be used for long distance transmission. Frequency response 80~8000Hz, inductively 32H, pressure-resistant 3kV, staged around the system. I find information, carefully designed circuit, this machine turns into a Hi-Fi amplifier, excellent results have been achieved.8FBservice manual download site
8FBservice manual download site
Machine circuit as shown in Fig. This machine uses the "long-tailed phase voltage + amplifier + push-pull output" mode. This "push-pull" zoom mode than traditional circuit has at least the following three advantages: first, the whole push-pull amplifier has a great effect on the common-mode signal, it is easy to improve the signal to noise ratio, distortion can be further reduced. Second, inverted relative to long-tail in the first level and promote low power voltage amplification, improving the load support and overcome the adverse effects of high output impedance, low capacity. Thirdly, the voltage amplification in the second level, gain and improved sensitivity, dynamics, elastic sense of distance and speed are significantly enhanced.8FBservice manual download site
8FBservice manual download site
In order to improve the output of symmetry, common cathode resistor is better replaced by a constant current source, to do more than one hundred per cent-Volt constant current source is too much trouble. This machine uses the most simple way, negative Dianyuan cathode resistor connected to the power supply, double 38V Dianyuan power transformer windings, Center tap is vacant, after a bridge rectifier can be -100V over bias, so cathode resistor can be increased to about 30k/1.

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