The project uses cheap and readily available vacuum tubes. The amplifier has a high output power, that allows you to work with current average set of speakers. Presented by the amplifier can be a great addition to your home audio system or work with musical instruments.
In the illustrated construction, the opposite output stage is used with lamps EL36 (more commonly used in the power section of the old TV circuits, than sound stages), as well as the classic single-voltage amplifier and an inverter to a common load with lamp ECF82 (equivalent to US). She 6GH8.
The use of these lamps to create a simple electric power amplifier 25 … 30 W / 8 AT. Amplifier designed as a monoblock. All the elements of the amplifier and power supply unit – The speaker and power transformers – are placed on the single-sided printed circuit board. Schematic diagram of the amplifier shown in Figure 1.
Input from the socket J1 is connected to the pentode portion V1-ECF82 (on the scheme, he is designated as tetrode, as a cathode connected to the third grid in the lamp) preamp. Resistor R1 closes polarization circuit, and R2 prevents excitation. Step works with an automatic polarization, obtained via the resistor R4. The global feedback signal is supplied to the lamp cathode through resistors R5 and R29, and a capacitor C1. Adjustable voltage divider Ug2, consisting of resistors R6, R7 and potentiometer RV1, allows you to select the operating point V1 so, that the amplified signal distortion is smallest. CE2 capacitor filters the power supply of the second network, while the C6 ensures stable operation stage. The amplified signal through the resistor R8 is supplied directly to the ultimate phase inverter, formed on the triode V1. Besides, typically via connecting capacitors it is fed to the control grid power lamps V2 and V3. The output stage has a constant polarization, negative voltage is supplied from the first grid rectifier BR2 filter capacitors CE6 and CE7 and the resistor R21. Potentiometers RV2 and RV3 allow you to set the operating point of the tip. Capacitors C5 and C6 additionally untie voltage power lamps Ug1. The voltage at the anode of the rectifier BR1 obtained from the filter on the capacitor CE5. Tension is further filtered by capacitors C1 and CE3, and resistors R6 and R9 to preliminary stage power inverter and. The diode D1 reduces the influence of the voltage change at the anode at a preliminary stage. Tension second grids is also filtered by means of resistor R26, CE4 and capacitance diode D2 and lowered to the desired value zener diodes DZ1 and DZ2 capacity 5 W. Resistors R22 and R23 counteract the excitation circuit. Resistors R27 and R28 can measure and fine-tune the current. Resistors R25 and R26 set the heating capacity to a safe value for the heater V1. Variables anode voltage, bulb, and the first grid obtained from the toroidal transformer 100 AND. The presented model works with the speaker transformer to Raa = 3 … 4 KB, Who> 30 W, He> 100 mA (For example, LO-PP-80/1 or equivalent) and a desired load impedance.
The amplifier is mounted on a single-sided printed circuit board, arrangement of components shown in Figure 2.
In the manufacture of printed circuit board should use a thicker PCB due to thermal and mechanical loads on board. On board a lot of ventilation holes to facilitate the circulation of heat around the lamp. The circuit in Figure EL36PP connection 3.
The wires must be shielded, mains voltage 220 VAC, tube anodes and anode voltage must be properly insulated. Network cables must be double insulated.