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
The voltage map of PVA18 main board is measured in these status. Please adjust your amp to these status.Because there are the differents between the electronic components, so it is normal that 10% fluctuation of voltage value between your amp with voltage map.
Voltage: DC
Standby ON
Contol: Gain and Master minimum
Biase voltage: -30V
Power tube: Pentode

PVA18 main borad voltage map

Voltage map of PVA18 main board
Start from down to up of board. The power supply filter circuit is on the downest of the board. The rightest is the rectifier bridge consisted by four diodes D1-D4, which provides full-wave rectify for 260 VAC from power transformer. From right to left, through different capacitors filting , the different plate voltages of the tube in amp stages are : B+A: 390VDC, B+B: 360VDC, B+C: 308VDC, B+D:270VDC (V2). B+E:255VDC (V2).
If you could not hear any sound opening amp, please check these voltage normal first, then check the points connected with them in tube sockets.The Plates of 12ax7 are Pin 1, 6, the plate of EL84 is Pin 3.
Then, the uppest line of the main board. Each one has the position code of one letter and two digits . The first letter “V” represent "Valve (Tube)". First digital means code of tubes, Second digital means code of pin of tube. For example : V2-3 reprent this point will be connected with No.3 pin of second vacuum tube.
Because this main board is universal board of our amps, so the position code printed on board are not totally consistent with real layout drawing of each amp. Please connect wires according to layout drawing of each amp kits.
PVA 18 has three amplify stages, V1B, V1A, V2B. The voltages of first 12ax7 tube are below: The anode voltage of V1B is 120VDC (V1-6 of board), The anode voltage of V1B is 190VDC(V1-1 of board). The cathode voltage of V1B is 0.9VDC (V1-8) and V1A is 1.8VDC (V1-3), the second amplify stage is clod bias.

PVA18 layout
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.
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.