9 Tube Stereo Amplifier

20 Watts per channel Maximum

Want big tube room filling sound without the trouble or expense of big tube equipment? Look no further! This 9 tube amp is simple to operate, powerful, and uses only 3 types of tubes. This amp features a 6BQ5 push-pull output for each channel, and two quiet, reliable 6EU7 tubes in each channel as well. A 5U4-G keeps plenty of power flowing. You have complete control with powerful bass and treble tone controls, and a balance control compensates for any speaker/room or source audio deficiencies.


The Magnavox-style output section uses a paraphase inverter and a minimum of circuit components. An inverse feedback loop minimizes distortion to give you clean, room filling tube sound. This is a powerful amplifier, if you live in a dorm room or small apartment, you may have difficulty, as this amplifier does not like to play at low volume levels.

Parts List

Control Resistors


Resistor ID

Value (ohms)

Function, Notes

R1A & B

Dual-section 500K audio taper 1/2W

Volume Control

R2A & B

Dual-section 1M linear taper 1/2W

Bass Control

R3A & B

Dual-section 1M linear taper 1/2W

Treble Control


750 linear taper 1W

Balance Control *See note at end of parts list.

Fixed Resistors



R5, R23

2.2K 1/2W

Input amp cathode

R6, R24

220K 1/2W

Input plate load

R7, R25

10K 1/2W

Bass tone comp

R8, R26

100K 1/2W

Bass tone comp

R9, R27

100K 1/2W

Audio coupling

R10, R28

2.7K 1/2W

Tone amp cathode

R11, R29

82K 1/2W

Tone amp plate load

R12. R30

470K 1/2W

Grid load

R13, R31

47K 1/2W

Grid input

R14, R32

5.6K 1/2W

Inverter cathode

R15, R33

2.2K 1/2W

Driver cathode

R16, R34

220K 1/2W

Plate load

R17, R35

220K 1/2W

Plate load

R18, R36

220K 1/2W

Output grid

R19, R37

39K 1/2W

Inverter grid

R20, R38

470K 1/2W

Output grid

R21, R39

220K 1/2W

Monitor isolation

R22, R40

3.9K 1/2W

Feedback coupling

Power Resistors




100 10W wire wound

Output cathodes


10K 5W wire wound

Voltage divider


33K 2W metal oxide

Voltage Divider


750 5W wire wound potentiometer

Hum adjust


Fixed Capacitors


Capacitor ID


Function, Notes

C1, C10

0.047mF 630V

Audio coupling

C2, C11

0.002mF 630V

Bass tone comp

C3, C12

0.02mF 630V

Bass tone comp

C4, C13

0.0002mF 630V

Treble tone comp

C5, C14

0.002mF 630V

Treble tone comp

C6, C15

0.047mF 630V

Audio coupling

C7, C16

100mmf 630V

B+ decoupling/snubber

C8, C17

0.0047mF 630V

Audio coupling

C9, C18

0.047mF 630V

Audio coupling


0.01mF 1400V

Line bypass

Electrolytic Capacitors




22mF 25V

Cathode bypass


47mF 450V



33mF 450V



10mF 450V



33mF 450V



Choke ID

Inductance (henries @ 1000 cps)

Current, notes


1 henry

130 ma @ 330 volts, U-bracket


Power Transformer, T1


Sec. 1

Sec. 2


117V AC 60cps .92A

600V CT 130ma

5 volts 3 amps

6.3 volts 4 amps


Output Transformers T2, T3

Primary Impedance

Secondary Impedance

8000 ohms,CT @ 400 cps

Matched to speakers, with a tap @ 4 ohms for feedback.


Miscellaneous Parts


Part ID


Function, Notes

SW1A & B

2-pole, 6-throw make-before break switch

Audio Selector Switch


Single-pole, single-throw switch, 5A rated

Power Switch



Input amp-tone amp left channel



Driver-phase inverter left channel



Input amp-tone amp right channel



Driver-phase inverter right channel



Output left channel



Output left channel



Output right channel



Output right channel



Current rectifier

*Note on balance control: If you want to omit this balance control, such as when using separate pots for the volume controls, see the balance control notes on the 7-tube output amplifier page.

Reader's Contributions

Newest contributions on top.

George in Ohio

1-27-14   George emailed me photos of his amp and this note:

"Wes, I used the schematic posted on your site, and built this. modified slightly with separate bass and treble on each channel. also, I moved the location of the balance control in the circuit, to lessen the load on the pot. I gave it two sets of switchable inputs. I used handmade parts boards. (similar to a fender) at this point I was testing it out. sounds very nice. I'm driving it with a Grundig Yacht Boy 300. I have to go back in to add the filter choke. I was anxious to try it out."

As You can see from the photos, George did a nice job with chassis layout, and has just done a real first-class job with the layout and construction. The silver top cage gives the finished rig a nice "classic" look.


DC Stelios

1-25-12  DC has written me several times with questions and comments about this schematic and was kind enough to share a few photographs of the amplifier he built from it. He has told me it sounds as good as it looks, and I believe it. DC did not use a commercially made chassis box, but built it himself and the results are very nice with the layout, color finish and wood ends. Also note the shielding partition DC built between the power supply and amplifier stages. DC chose the asymmetrical chassis layout you see here for minimal hum. Note the very clean layout that DC designed for the circuit components in the chassis underside views. DC has been very picky about component and interconnect lead dress, and I believe it has paid off in the amp's performance.

Click on any picture to enlarge

If you too have built this amp, then email me a few pictures if you like, and I'll add them here with a few comments. Just email them to the address shown in the contact info on the Radio Page in the link below.

Created 11-21-09

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