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Mugen: A Hybrid Audio Amplifier

The best of both worlds?

Mugen: A Hybrid Audio Amplifier

Valves (or ‘vacuum tubes’) are experiencing a real revival in the audio world, which can readily be seen from the large number of commercial amplifiers and DIY designs that have appeared in recent years.

Unfortunately, valve amplifiers are relatively costly compared withtransistor amplifiers, in part due to the need for a high voltage supply and output transformers. Output transformers in particular are a major investment.

This design attempts to remedy this situation by replacing the output valves and transformer.

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Extra info / Update

5 February 2008.

In the parts list, the value of R11 is erroneously given as 18 ohm. The correct value is 18 kohm.

The correction has been incorporated in the parts list on the project web pagee.

Component list

amplifier & power supply

(for a stereo version, all components must be purchased double)


(1% metal film, 600mW unless other rating indicated)

R1 = 392k

R2,R5,R12,R20,R32 = 1k

R3,R4 = 150kΩ 2W (BC PR02 series)

R6,R15,R19,R45 = 100(

R7 = 22kΩ 3W (BCPR03 series)

R8 = 2kΩ43

R9 = 274(

R10 = 560(

R11 = 18k(

R13,R17 = 392(

R14,R18 = 2Ω2

R16 = 20k

R21,R22 = 0Ω22 4W (Intertechnik MOX)

R23 = 10( 2W

R24,R26 = 182(

R25 = 1kΩ5

R27 = 3kΩ3

R28,R29 = 1M

R30 = 330k

R31 = 10M

R33, R34, R35 = 100k

R36 = to be determined (0.22( using 3N604)

R37,R38 = 100( 1W (see text)

R39 = 330(

R40 = 82kΩ 3W

R41 = 150kΩ 3W

R42,R43 = 1kΩ 1W

R44 = 4Ω7

P1 = 2kΩ,15-turn preset, T93YB (Vishay) or 3296Y (Bourns)

P2,P3 = 5kΩ,15-turn preset, T93YB (Vishay) or 3296Y (Bourns)


C1 = 100nF 400VDC

C2,C3 = 3(F3 400VDC (ClarityCap SA 630 V audiograde capacitor)

C4,C6,C8,C10 = 270(F 50V (Panasonic FC, Farnell # 9692436)

C5,C9,C12,C14,C22 = 100nF 50V

C7 = 100nF (Vishay MKP-1834, Farnell # 1166887)

C11,C16,C17 = 10(F 50V

C13 = 47(F 50V

C15 = 1(F 250V (e.g. Wima foil capacitor, see text)

C18 = 22(F 63V

C19,C20 = 47(F 25V

C21 = 220(F 50V

C23 = 2nF2 (Wima FKP-1/700 VAC, see text)

C29,C30,C31,C35 = 2nF2 (Wima FKP-1/ 700 VAC)

C24 = 150(F 450V

C25 = 100nF 450 VDC

C26 = 10(F 400V

C27,C28 = 22(F 400V

C32,C33,C34,C36,C37,C38 = 4700 (F 63V (BC056, 30x40 mm, Conrad Electronics # 446286-89)

C39 = 10(F 25V

Cfb = 56pF (optional)


D1 = not used

D2,D3 = UF4007 (if necc. 1N4007)

D4,D5 = 1N4001

D6,D7,D8 = 1N4148

D9,D10,D11,D12 = BY228

D13 = 1N4007

LED1 = LED, 5mm, red

Z1 = zener diode 110V 1.3W

Q1 = BD139

Q2 = 2SC2073

Q3 = 2SA940

Q4,Q5 = 2SC5200

Q6,Q7 = BC550B

Q8 = BS170

Q9,Q10 = BC547B

Qbax = 2SC1815BL

U1 = LM337

U2 = LM317

U3 = TL783 (Conrad Electronics # 175012-62)


V1 = ECC83 (pref. JJ Electronics)

V2 = ECC88 (pref. JJ Electronics)


B1 = bridge rectifier 600 V piv @1A (DF06M)

B2,B3 = bridge rectifier 400V piv @ 35A

T1 = mains transformer, sec. 30V + 250V + 6.3V (Amplimo type 3N604)

T2 = mains transformer, sec. 2x28 VAC, 300VA (Amplimo type 78057)

RLY1 = output relay 24V (e.g. Amplimo type LR)

Heatsink profile for U3 (Fischer SK104 25,4 STC-220 14K/W (e.g. Conrad Electronics # 186140-62)

Heatsink profile for U1 and U2, Fischer FK137 SA 220, 21K/W (e.g. Conrad Electronics # 188565-62)

Heatsink profile for Q4 and Q5, 0.7K/W or better

9-way valve socket (Noval), PCB mount, for V1 and V2

Amplifier board, no. 070069-1 (mono)

Supply board, no. 070069-2

Suggested suppliers

Toroidal transformers and output relay:


ClarityCap SA capacitors:




(OEM like Soniqs SAX)
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