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


6V6 6J5 Class A valve tube audio Amplifier schematic

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

Valve (Vacuum Tube) Audio Amplifier Circuit Wiring Schematic

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

Valve Vacuum Tube Audio Amplifier Power supply Circuit schematic

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.

vacuum tube Audio Amplifier Transformer Magnetic flux Diagram


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.

6V6 6J5 Class A Vacuum Tube Audio Amplifier Wiring Circuit  Vacuum Tube Valve Audio Amplifier 6V6GT Valve Amplifier Circuit Chassis Design

Please send your ideas, which are very important for our success…

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15 comments on “6V6 6J5 Class A Vacuum Tube (Valve) Amplifier Circuit
  1. Enrico says:


    R6 has to be mirrored, attaching R7 to the central terminal and C5 to the upper terminal otherwise the input impedance decreases as you decrease the volume shorting the input source at 0 volume (very bad).
    Also I would increase the input resistor (again R6) to 50K LOG pot.


  2. m says:

    thank for help me
    ineen more pleas

  3. Zdeno says:

    Hi !
    What about R1 in power supply ???

  4. battler breton says:

    R1 in the power supply is,or should be
    a “bleeder”,used to empty the big caps
    of their charge when not in use,high voltage
    remains and can be dangerous!
    The good value must be around 100KOhm
    the 100Ohm one should stand 900watt !Nice
    show on first and single start…

  5. admin says:

    battler breton :

    R1 in the power supply is,or should be
    a “bleeder”,used to empty the big caps
    of their charge when not in use,high voltage
    remains and can be dangerous!
    The good value must be around 100KOhm
    the 100Ohm one should stand 900watt !Nice
    show on first and single start…

    6V6 6J5 Amplifier Power Supply R1 Resister
    This is my spelling mistake. R1=100KΩ. I correct it. Thanks!

  6. admin :
    Thank you very much! I corrected my circuit diagram. But i still used 10K pot.

    thank you for shareing!

  7. William says:

    Hi, I am based in the UK, the power voltage is 240 volts. Could someone please tell me how to modify the power supply circuit so it could take 240 volts and step it up to 300 volts, Thank you.

  8. sax says:

    c5 must be after pot, before r7,
    non polarized.
    the best value is 0.1uF.
    after r7 must be grid resistor.
    the best value is 470k.
    c2 may be 100uF, best choice is tantalum.
    c3 may be larger, up to 0.47uF or 2x 0.22.
    c4 may be larger, 100 – 220uF.
    6v6 must have g2 (pin 4) resistor
    1 – 2.2K, then go to supply.

    output transpormer primary may be
    paralellized with 220pF 1500v.

    power supply must have stand by switch,
    after the first capacitor, because first
    must warm up tubes, about 30 sec.

    power supply may be combined with rectifier tube +
    2 pieces of silicon diodes for slower high voltage
    applying to tubes. best choice is may be 5y3gt.

    there is example on the internet.

    for the output tube, choice is very good.
    best sounding tube, after the 2a3.

  9. Hector J Ruiz says:

    C5 is fine just where it is! R5 and R7 puts the grid at 0-volt potential. Placing C5 after the R5 pot would isolate the grid from ground and screw up the bias potential between the cathode and grid. In reality the cathode current flowing through R2 makes the cathode slightly positive. This is an OLD TRICK that makes the grid appear to be Negative with respect to the Cathode. If it were this way the tube would ‘super’ conduct and burn up. Vacuum tube require REVERSE bias as opposed to transistors which require FORWARD bias.

  10. chan HJ says:

    This is very common& basic single end power amp. If to improve the quality of sound that to be selected good components to replace it. As Output Transformer’ Tube; and capacitors.

  11. Peter says:

    Hi there,
    Do you have any details, how to construct the output transformer?
    For instance which should be the primary impendance, resistance and secondary.
    Any help will be much appresiated.


  12. Raja Naz Aiman says:

    Hey there! I’m building this amp for my college project and I can’t seem to find a transformer that offers an output of 230VAC and 6.3VAC as well.. I was wondering if it’s possible for me to get the 230VAC from the primary windings of the transformer? THANKS!!

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