JHL HOOD 1969 small class A amplifier board

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JHL HOOD 1969 small class A amplifier board [Copy link]

This push-pull output transistor amplifier HOOD1969 designed by American JHL in 1969 is timeless. Although it has only a Class A 10W output, the volume can be comparable to a 50W home amplifier. The high frequency is delicate, the extension is very good, the mid-frequency is thick, and the low frequency is full. It is the best choice for listening to vocals and music! The recommended power supply is a transformer greater than 300W, and the output AC is a single 20V--26V (the on-board components are designed for 22-24V). The debug midpoint voltage is 1/2 DC voltage, and the whole machine current is adjusted to 1.5A--2A. The figure below shows the waveform of the oscilloscope at DC 26V, input 1KHZ audio signal, input amplitude of 0.65V, and current of 1.6A. It is perfect~~~~! The debugging method is: first replace R1 and R7 with adjustable resistors, and adjust the adjustable resistors of R1 and R7 to the maximum resistance! Adjust the resistance of R1 (100K), the multimeter is in the DC 50V gear, the red test pen is connected to the positive pole of C4, and the black test pen is grounded. The output midpoint can be adjusted to 1/2V power supply voltage. Next, adjust the adjustable resistor of R7, put the multimeter in the 5A position, connect the red test pen to the positive pole of the DC filter output, and the black test pen to B+. Adjust R7 so that the reading is 1.5A-2A (depending on the radiator temperature, the radiator temperature is high, the current is adjusted to a small value, and the temperature is low. The current is adjusted to a large value, but the maximum should not exceed 2.5A). After adjustment, test the midpoint voltage to be 1/2V power supply voltage. Then monitor the current size and control it at 50-80C° after the radiator temperature rises. PCB specifications: 10*10 board thickness 1.6mm fiberglass board surface color is single-sided red solder mask, and the silk screen color is white. The output tubes are gold-sealed triodes and plastic-sealed triodes. The entire board only has one jumper when the plastic-sealed triode is installed. The high-current traces are all tinned. This board is equipped with a brand new original MOT3055 power tube.