How to use voltage map of UT18 main board

KLDguitar UT18K is assembled kits of 18w hand wired dual independent channels guitar amp based on VOX AC15 which was one of the first to define the British sound and continues to be used on stages and in studios around the world. The voltage map of main board of each tube guitar amps, could help hobbyists to understand tube amp principle and find assembly questions.

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 UT18 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

UT18 main board voltage map

Voltage map of UT18 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: 360VDC, B+B: 347VDC, B+C: 288VDC, B+D:241VDC (V2). B+E:230VDC (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.
UT 18 has dual independent channels, which signals need be controlled by separately .V1B amplifies signals of clean channel, the gain is controlled by VR2.V1A amplifies signals of lead channel,the gain is controlled by VR1.There are four points on the main board relationship with first preamp: V2-7,V2-8, V2-3, V2-6.
V2-7 connected with Pin 1 of VR1, its DC voltage is 0 VDC. V2-8 connected with Pin 3 and 8 of first tube. Pin3 and Pin8 are cathodes of 12ax7, the DC voltage of them is 1.6VDC. V2-3 and V2-6 connected with Pin 6 and Pin 1 of V1 individual. They are two anodes of 12ax7, the DC voltage are 174VDC and 179VDC.

UT18 layout
V6-2 on the main board connected with Pin1 of VR1, the voltage is 0VDC. V6-6 on the main board connected with Pin3 of tube V2, it is the cathode of V2A, the voltage is 150VDC, V2A is high voltage cathode follower which mainly adjust the impendance of amp.V6-8 connected with the Pin8 of V2, it is the cathode of V2B, the voltage is 1.2VDC.
V6-1 on the main board connected with Pin2 of the Treble control ,its voltage is 0VDC. V3-7 connected with The Pin7 of V3, it is grid of V2B , the voltage of grid of V2B is 37VDC. V3-2 connected with the Pin2 of V3, it is grid of V3A, the voltage is 36VDC. V3-3/8 connected with the Pin3 and Pin8 of V3 , they are cathodes of V3A and V3B. The Voltage is 54 VDC . V3-6 on the main board connected with the Pin6 of V3, it is anode of V3B, the voltage is 232VDC. V3-1 connected with the Pin1 of V3, it is anode of V3A. The voltage is 225VDC.
V5-2 connected to the pin2 of V4 through R40,V4-2 connected to the pin2 of V5 through R41, Pin2 of EL84 is grid 1 the voltage is 0VDC. V4,5-3 connected with Pin3 of V4 and V5, Pin3 of EL84 is cathode , the voltage is 12.6VDC. Pin7 is anode of EL84. V4-9 connected with Pin9 of V4, V5-9 connected with pin9 of V5, Pin9 of EL84 is grid2, the voltage is all 350VDC.