The system is based on the ATTINY26 [U2] microcontroller. The current measurement is carried out indirectly on resistance with a resistance of 1R, connected to the cathode circuit of the tubes, as shown in Figure 2. In order not to have a significant effect on the tube working point, the resistor must have a slight resistance. The voltage corresponding to the current is intensified by 10 times by amplifiers of the U1 system and is supplied to the analog-digital converter built into the U2 microcontroller. The measurement result is displayed on the LCD screen with a resolution of 2 line X 8 characters attached to the X2 connector. Depending on the tuning of the jumper X3, you can make measurements in one (monoblock) or two channels [stereo -power].

The transistor Q1 with related elements controls the voltage relay with a delay on the anode, which is set for 60 seconds. The countdown is displayed on the LCD display.

The power system is typical and does not require a detailed description. As a power source, a small transformer was used 2VA, galvanically untied with the amplifier circuit. This increases the flexibility of the applications, but each time in the case of a stereoamplifier, check if the connection of the amplifier malfunction will cause the connection.

The potentiometer RV1 allows you to set the contrast, the resistors R7 and R8 are responsible for the intensity of the backlight. The model uses a backlight display, perfectly combined with tube radiators.

The system is assembled on a double-sided printed circuit board, the assembly scheme of which is shown in Figure 3. The typical assembly method: first we mount the SMD elements, then elements of the through opening, then the LCD-display, which is a mechanical base of the system and is connected to the plate using a 2-lane outlet. x 2.54 mm. The display mounting holes are used to assemble everything in an amplifier. Make sure they are not connected to the grounding of the system. In this case, it should be installed with isolated couplings to avoid grounding contours in the system.

The system does not require launch, you only need to set the contrast of the display and choose the number of measuring channels.