







Single Ended Class A 6V6 6J5 Valve (Vacuum Tube) Amplifier Circuit

This is my first successful vacuum tube project. The output of this small amplifier in which a 6V6GT output pentode is connected as triode is about 4.5 watts.

This project involves a single ended audio amplifier, which consists of a resistive input network, a driver stage, and an output stage to a typical 8 ohm loudspeaker load, all the while, using a minimum of supportive passive components for biasing and coupling duties. Power-supply voltage is provided by full wave diode rectification of 230 VAC by a magnetic transformer. This design provides a quality audio amplifier.

Valve amplifier circuit diagram

PARTS LIST R1 470Ω 1W R2 4.7KΩ 1W R3 1MΩ ¼W R4 100KΩ 2W R5 15KΩ 2W R6 10KΩ Volume Control R7 1kΩ ¼W C1 33µF 250V C2 33µF 250V C3 0.1µF 400V C4 10µF 250V C5 1µF 100V V1 6V6GT Tube V2 6J5GT Tube T1 Audio Output Transformer, Primary 5KΩ; Secondary 8Ω LS1 10W 8Ω Speaker

The major factor involving the design of this single ended output stage is matching an available output tube to an available output transformer (OT) , which can provide the proper impedance matching. Using typical operating parameters, the 6V6 power tube, operating in triode mode, has an ideal load impedance of 5k Ohm, and generates about 4.5 watts of power. An OT was used, handling 8 watts and providing impedance matching from a 5k primary to an 8 ohm secondary, which is a common loudspeaker impedance.

Tube amplifier power supply

PARTS LIST R1 100KΩ 3W C1 0.047µF 400V C2 0.047µF 400V C3 0.22µF 1000V C4 220µF 450V D1-D4 1N4007 F1 500mA Fuse S1 Switch DS1 Neon Lamp T1 Mains Transformer, Secondaries 230V, 150mA; 6.3V 3.5A

The amplifier uses a simple linear power supply to develop 300VDC. Heater voltages are supplied directly from the 6.3VAC taps on the secondary of the power transformer. The other secondary windings, rated at 230VAC are used for the DC supply. It consists of a 4 rectifiers, variety of smoothing capacitors and resistor.

Tube Datasheets

6J5 Datasheet

6V6 Datasheet

Several construction issues were considered in the building of this amplifier. High power supply voltages, large and leaky inductive components, and high temperatures are among these considerations. I used old tube amplifier chassis.

Magnetic flux is expelled from the transformers as shown by the red arrows above. By placing the output transformer (OT) and power transformer (PT) at opposite ends of the chassis, and rotating their axes 90° from one another, induction noise from PT to OT is reduced. Although this configuration sees flux from the OT directed at the 6V6, OT flux interference into the sensitive preamp stage tube is avoided. Beneath the chassis hum reduction is further achieved by winding all pairs of wire containing AC (filament heater wires, PT primary, and secondary wiring to the diode rectifier).

6V6 Tube amplifier Video

Due to the 300V power supply voltages used, components were carefully chosen to withstand peak conditions.

Connect amplifier ground and power supply ground to the chassis ground point.

Don’t touch any component when the tube amplifier connected to the power, because it used high voltage.









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