6MB8 low power tube power amplifier

Three 6BM8 high μ triode and pentode composite tubes were obtained. This tube is used as an oscillator and power output tube in the field scanning oscillator and field output circuit of the TV. It is now used in tube amplifiers as Class A power amplifiers, making them rejuvenated and contributing to the field of audio.

The circuit is simple and clear. A 6BM8 tube and a triode form the front-stage RC coupling voltage amplifier, and the open-loop gain is about 56 times. In order to improve the characteristics of the amplifier, a negative feedback of about 7dB is added from the secondary of T (output transformer) to reduce distortion. The 150pF capacitor in the negative feedback circuit is mainly to prevent the super-audio phase shift from self-excitation. The input sensitivity is 0.6V, which is very suitable for current CD, radio head, MP3 and other sound sources. The pentode is a power amplifier. Although the output power is less than 4w, it is very suitable for bedside audio.

The attached picture shows a channel circuit. This circuit uses semiconductor diode rectification, and the sound quality is relatively hard. The full-wave rectifier 6Z4 can be used as it. The coupling capacitor of the whole machine was changed and listened to many times by the author, and finally the oil-immersed capacitor was selected.

This machine has nothing special about it, its biggest features are "small" and "beautiful". As long as it is carefully made and made of good materials, it will bring you unexpected surprises!