Blackheart BH5H Just like the Bad Cat Mini Cat, Epiphone Valve Junior, Dr. Z Mini,etc it runs a 5 watt cathode biased EL84 power-tube, which operates in SE Class A mode. It has two tubes, a 12AX7 for the preamp and an EL84 for the power-tube and offers a 3-band EQ. The EL84 tube is switchable from 3 watts (triode) to 5 watts (Pentode). This is the original Blackheart BH5H board, the original 5 watt 1k dropper resistor has burnt a hole in the board and has been replaced with a 10 watt 1k resistor. A dropper resistor at 1K(1000r) makes calculating current draw easy.   Volts/Resistance = Current. If 42 volts is dropped across this resistor, the amp is drawing 42mA.  (42/1000 = .042 Amps or 42mA). Lowering the value of dropper resistor will raise the B+ Voltage The stock PCB design has the heater traces running too close to the preamp circuit. Even the good ol' Alnico kit has you cutting the traces on six PCB tracks and then rewiring them to reduce heater buZZ. A new board is built using G-10 Garolite, Parts are laid in position and holes are marked for the eyelets. Holes are drilled into the chassis to mount two extra tube sockets. A GZ34 tube rectifier replaces the solid-state Rectifier and a 6AQ5 pentode power tube is added, chosen for its ability to give the user a full dose of second order harmonics. The 3 watt/ 5 watt switch now swaps between a 3 watt pentode (6AQ5), originally triode(EL84) and a 5 watt pentode (EL84). Trying to keep the 3 pot tone stack as original as possible, but end up reducing the value of R5 to about 35k to improve the tone. This is easily tested by using alligator clips to connect resistors in parallel with R5 Because of the differences in voltage requirements for the power tubes a 3PDT toggle switch is needed to swap between the power tubes. On the EL84 the plate is about 310 volts drawing 38mA and the screen is about 300 volts drawing 4.2 Ma. At node A, the voltage rail is connected to the centre pin on the 3PDT switch with the top pin going to the blue wire from the output transformer and the bottom pin going through a 1.2k resistor and back to the blue wire from the output transformer. This resistor will drop about 50 volts from the plate voltage when the 6AQ5 is operating. Connected to the centre pin on another node of the 3PDT switch is the red wire from the output transformer, with the top pin connected the plate of the EL84 and the bottom pin connected to the plate of the 6AQ5. At node B, the voltage rail is connected to the centre pin on another node of the 3PDT switch with the top pin going to the screen of the EL84, and the bottom pin going through a 22k resistor to the screen of the 6AQ5. This resistor will drop about 70 volts from the screen voltage when the 6AQ5 is operating. The BH5H uses 47uf at C13 the first filter capacitor, this value is lowered to 22uf because the tube rectifier will see this capacitor as a short until it is topped up.  For C12 an 80uf capacitor smooths the supply voltage to the plate of the power tube through the 3PDT toggle switch. The BH5 is a cathode biased amp using an EL84 power tube with a Maximum Plate Dissipation of 12 watts. Exceeding this value can dramatically shorten the life of the power tubes and possibly cause major problems if one should fail while in operation. No two power tubes are exactly the same. Some may move more current than others. Whenever you change the tubes you should check the bias. To get the Cathode Current measure the voltage drop across the cathode resistor then divide this by the value of the cathode resistor. Ground the (-) lead of the Multimeter, Use the other lead (1 hand only) to Probe pin3 on the EL84 tube socket. This will give you a Cathode Voltage of 10 volts. Cathode Voltage (10 volts) / Cathode Resistor Value (250 ohms) = Cathode Current .04amps or 40mA). The Cathode current will include both the Screen current and the Plate current. The Screen current equals the voltage drop across the screen resistor divided by its value. A 4.2 Volt drop across a 1K screen resistor indicates 4.2mA of screen current. The screen current is for an EL84 is 4.2mA. Subtract the Screen current from the Cathode current to get the Plate current. Cathode current (40mA) - Screen Current (4.2mA) = Plate Current (35.8mA). Ground the (-) lead of the Multimeter, Use the other lead (1 hand only) to Probe pin7 on the EL84 tube socket. This will give you a Plate Voltage of 310 volts. Plate Voltage (310 volts) - Cathode Voltage (10 volts) x Plate Current (35.8mA) = Plate Dissipation (10.74 Watts). Recommend Keeping plate dissipation between 10.5 and 11.5 Watts for an EL84. To reduce excess power dissipation. 1/ Reduce the Plate Voltage. The 1k Dropper resistor controls the B+ Plate Voltage. Increase this value to lower the B+ Plate Voltage. 2/ Lower the Cathode current by increasing the value of the Cathode resistor. Cooling the power tube improving tone and increasing tube life.