DIY 50W Gallstone Amplifier

The more mature LM1875 integrated amplifier is used to make this gallstone amplifier. The electrical schematic is shown in the figure.

To make a circuit board with fiberglass board and rivets, a 1.5mm thick board is needed. If it is too thin, the strength is not enough. The area of ​​the board is 160mm×200mm. According to the requirements of the schematic diagram, the author draws the location of the components with a pencil and then punches holes. Rivet it with 1.3mm hollow copper rivets. No rivets are needed for the integrated amplifier block, bridge stack, fuse and heat sink bracket.

After the substrate is processed, welding begins.

This 50w tube power amplifier uses a 6N3 as the tube pre-stage, half of which is used for amplification and the other half is used for cathode output. Why is the cathode resistor R5 so large? Because the cathode potential is high, it can be close to the plate potential of the amplifier tube. The plate current of V1 is about 2.6mA, and the plate current of V2 is about 2.4mA, working in the amplification area.

The gain of the integrated amplifier (LM1875) can be smaller, and R7 uses a 1k0 resistor. Because the output level of the pre-stage tube is very high, it is enough to drive the full power output of the post-stage. The heat sinks of the two integrated amplifier blocks (LM1875) should be as large as possible to facilitate heat dissipation.

The audio input sensitivity of this machine is 150mV-200mV, and the output power is 2x25W.

It is not easy to make a successful DIY. Audio enthusiasts who like gallstone amplifiers can refer to this.