The production of automobile tube amplifier

The circuit of this machine is shown in the attached figure. The voltage amplifier stage is connected in parallel by the common high-s dual triode 6N1 to reduce the internal resistance. The amplified audio signal is directly coupled to the inverting and driving amplifier stage, which is also served by the dual triode 6N1. The inverted and amplified audio signal is coupled to the push-pull power amplifier composed of 6P1 through a capacitor, and the gate adopts a self-supplied gate negative voltage. The power supply of each electron tube filament is provided by the car battery (12v). The filaments of the two tubes in the same channel are connected in series and directly connected to 12v. The output transformer adopts an E-type iron core with an area of ​​22mm×40mm. The primary uses φ0.2mm high-strength enameled wire with 644 turns in parallel (equivalent to a total of 1288 turns), and taps at 456 turns as the power supply end of the tube screen grid (the end is connected to the v3 and v4 screen electrodes, and the end is 188 turns away from the tap). After the primary winding is completed, the wires at the tap and the beginning should be cut off, so that there are two wire ends at the initial end, four wire ends at the tap, and two wire ends at the end, and then these wire ends are connected to form the coil winding shown in the figure, paying attention to the winding phase. The secondary uses φ0.86mm high-strength enameled wire to wind 102 turns, tapped at 72 turns, as a 4Ω output terminal (total output impedance is 8Ω).

The power supply circuit is bounded by the core of transformer T2. On the left is the self-excited oscillation circuit, which converts DC into AC. On the right is the boost, rectifier and filter circuit, which provides gate and screen voltages for the electronic tube. The power of T2 should be greater than 70w. The author uses a 75 "u" type core. The primary winding is wound with φ1mm high-strength enameled wire in parallel with 44 turns. The tap is at 22 turns, and the tap is connected to the negative pole of the 12v DC power supply. The secondary winding is wound with φ0.2mm high-strength enameled wire for 1030 turns. The remaining components are marked in the figure. As long as the components of the power supply circuit are normal and the welding is correct, it will generally be successful. During debugging, disconnect the connection to the power amplifier circuit, connect a 220V/60w incandescent bulb between the B3 terminal and the ground, close the switch s, and then adjust R1 and R2 to make the bulb brightest (R1 and R2 can be replaced by double-connected coaxial potentiometers, and then replaced with fixed resistors after adjustment). At this time, the voltage across the bulb should be within the range of 250-280v. Otherwise, check the battery and related components. The oscillating tubes BG1 and BG2 should be paired, and the β value should not be less than 50, otherwise it is difficult to oscillate, and the reverse pressure should be greater than 100v. BG1 and BG2 can be installed on the side panels of the machine box and insulated with mica sheets.

The frequency response of this machine is 20Hz~20KHz, and the rated output power is 10w+10w. After the machine is successfully debugged, the volume potentiometer and the power switch S can be drilled and fixed on the machine box facing the direction of the driving platform. Then drill holes in the corresponding places of the glove box of the driving platform to expose the volume potentiometer knob and the power switch push rod, and install the control knob. Then, the audio signal output by the original radio/playback box on the car is connected with a shielded wire, and the signal is properly attenuated before inputting into the power amplifier. If there is extra space in the car, the size of the speaker can be appropriately increased, so that the bass can be more powerful. Put sponge under the machine box and around the appropriate position to prevent shock. Next, use a φ2.5mm drill bit to drill four holes in the appropriate positions in the front and back of the glove box, and then use φ3mm self-tapping nails to fix the power amplifier. Finally, use a φ3mm drill bit to drill several rows of small holes on the glove box cover (that is, the power amplifier). The area is approximately equal to the area of ​​the machine box so that the heat can be dissipated upwards, and the entire production process is completed.