How to use voltage map of PVA18 main board
KLD PVA18 is hi gain guitar amp based on Marshall TMB18. It has two presence control. "SKY" is used for high freq sound , "Earth" is used for low freq sound. The power amp is Class AB amp of two EL84 tubes. The voltage map of main board of each tube guitar amps, could help hobbyists to understand tube amp principle and find assembly question. Please pay attention: The inner of tube guitar amp has fatal high voltage. If you have not enough skill and experience in high voltage circuit, Do not try to test it . Measure condition of voltage map |
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Voltage map of PVA18 main board |
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The second tube V2B is the preamp, V2A is high voltage cathode follower which mainly adjust the impendance of amp. Pin7 is grid of V2B, it connected with V2-7 of the board, voltage is 0VDC. Pin8 is the cathode of V2B, it connect with V2-8 of board, the voltage is 1.4VDC. Pin3 is the cathode of V2A, It connected with V2-3 of board, the voltage is 170VDC. |
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The third tube is long tail phase(LPT) inverter of PVA18 amp.The grids ( Pin2, 7 ) of V3 connected with V3-2 and V3-7 of the board, the voltages are 23VDC all. The anodes( Pin1,6) of V3 connected with V3-1 and V3-6 of the board, the voltage of V3-1 is 240VDC and V3-6 is 250VDC. The cathodes of V3 are Pin3 and 8 of tube, they connected with V3-3/8 of the board , the voltage is 35VDC. There are nine pins in EL84 tube. Pin4 and 5 are pins of filament. Pin7 is plate(Anode). The pin 9 is grid 2(Screen grid), Pin2 is grid 1( Control grid). Pin 3 is cathode or grid 3(Suppress grid), and three NC pins ,Pin 1,Pin6, Pin8. The power amp of PVA18 is class AB amp used two EL84 tubes: V4 and V5. The pins of these two tubes connected with the main board include: Pin 5(Filament) connected with board 6.3VAC.The Pin9(Grid 2) of two tubes connected with V4-9,V5-9 of the board, voltages are 360VDC.The Pin 2 of two tubes (Grid1) connected with V5-2 and V4-2 of the board, all are 0VDC. The Pin3 of V4 and V5(Cathode) connected with V4/5-3 of the board, the voltage is 16VDC. |