1. The circuit board adopts JLH1969 classic circuit design, and the PCB board adopts double-sided gold plating process, which is sturdy and durable. 2. Precision pairing of transistors 3. Aviation grade magnesium alloy angle aluminu 4. Capacitors use high quality German , Japanese , ruby and other materials 5. Resistance: copper foot metal film, 5-ring precision The finished board is an assembled, adjusted and tested amplifier boards of the classic JLH (John- Hood) 1969 class A amplifier. While JLH 1969 is a simple design, it is still one of the best transistor amplifier. Gold seal pipe: small pipe 2N2907, middle pipe 2N1711, pipe 2N3055 or ON3055.ON15024 Application: Suitable for listening to vocals, you can choose 3-5 inch full-range speakers; you can choose 5-8 inch full-range speakers for listening to bass, or you can choose 2 way speaker with power 120 , 8 inches or less, and true sensitivity above 86. The midpoint of their own adjustments / quiescent current : Tune midpoint: universal table hit voltage profile, black pen then the red pen then GND TP1 test holes (TP1 at the output capacitor positive) board, the adjustable resistance KT1 it is 1/2 of the supply voltage. Modulated current: 10A universal table hit stalls, a pen then positive power supply, the other one pen then VCC terminal, adjust the adjustable resistance KT2 change the current board size. Input voltage: Recommended 100-150W transformer, voltage output 12-26V.18-19V transformer works well Output power:Class A 10 , quite ordinary 35 . Colour:As Shown Material:plastic Size:Finished board size:100mmx73mmx30mm Package Contents: 1 * Amplifier Audio Board DIY Kit Only the above package content, other products are not included. Note: Light reflection and different displays may cause the color of the item in the picture a little different from the real thing. The measurement allowed error is +/- 1-3cm.