Mapletree Stealth 5 Manuale utente

Stealth 5

Monobloc Power Amplifier

User’s Manual

Rev. May21/03

Mapletree Audio Design

Lloyd Peppard

R. R. 1, Seeley's Bay, Ontario, Canada, K0H 2N0

(613) 387-3830

peppardl@post.queensu.ca

http://hollowstate.netfirms.com

Introduction _

The Mapletree Audio Design Stealth 5 Monobloc Vacuum Tube Power Amplifier offers

the audiophile a number of unique features:

♦ Exclusive use of high quality new old stock (NOS) tubes that can be obtained at

modest cost from many suppliers. The tubes provided are North American

manufactured brand-name types and should exhibit a long life in this application.

♦ Class A push-pull beam power tetrodes delivering 6 Watts output power at low

distortion.

♦ Soft-start vacuum tube rectification.

♦ Wide frequency response: 20 Hz – 20 kHz –1 dB at 5 Watts power output.

♦ Input volume control and high sensitivity of 0.3 V permit use without a line preamp if

desired.

♦ DC heater power supply for low noise.

The MAD Stealth 5 is a monobloc audio power amplifier with integral power supply.

Two units are required for stereo reproduction. While the input level control can be used

to set the volume level when feeding the input directly from a line-level source, the use of

a line preamplifier is recommended for convenience and flexibility.

For first-time operation, the 5 tubes must be inserted in the sockets in the positions

shown in the layout drawing which follows. Carefully align the key on the tube spigot

with the notch in the socket before pushing into place. When removing tubes, wiggle

slightly as you pull. Tubes supplied are normally 12 Vheater types so make sure the

heater voltage selector switch is in the 12 V position (with the “12” visible).

Controls_____

The rear panel layout shown below includes (right to left) the IEC ac line cord receptacle,

the fuse holder (2 A fast blow fuse required), the speaker binding posts (black is ground),

the input level control, and the RCA line input jack. A knob can be attached to the level

control if it is to be used as a volume control.

The front panel layout includes an ac power switch on the left and a pilot light on the

right. Pressing the power switch on the white dot turns the unit on. A standard IEC

detachable line cord connects the ac receptacle to a grounded 115-125 V, 60 Hz ac

supply. The chassis is connected to the ac line ground.

For normal operation with a line preamplifier, the level control should be set to maximum

position and the preamp volume control used to set the loudness level. For preamps with

high gain, it may be desirable to adjust the level control on the Stealth 5 to enable the

preamp volume control to operate around its mid position at normal listening levels.

Input/Output___

The preamp line output is connected with a shielded RCA interconnect cable to the

Stealth 5 input jack. The input impedance of 100K Ohms is high enough for driving with

any solid-state or tube preamplifier.

The speaker output is factory wired according to the customer’s specifications, typically

8 Ohms. If a different impedance is required, the output circuit must be re-wired

internally. Consult Mapletree Audio Design or a qualified technician. The output

transformer wiring diagram is included in the appendices of this manual.

Chassis layout _

Tube replacement and experimentation_____________

The tubes supplied are 12 V heater, metal envelope types. These are new old stock (NOS)

tubes that are not currently manufactured. While the types used are selected partly for

their availability and reasonable cost, some substitution may be necessary or desired

accordingto the listener’s tastes. All of the types used are available at higher cost in glass

versions. The equivalence is shown in the following table.

Metal type Function Glass type

12A6

12SC7/6SC7

12SJ7/6SJ7

5Z4

Beam power output

Phase splitter

Voltage amplifier

Full-wave rectifier

12A6GT

6SC7GT

12SJ7GT/6SJ7GT

5Z4GT

Note that if you want to use the glass 6SC7GT, you will need to use a 6SJ7 or 6SJ7GT as

there is no 12SC7GT type. You can substitute a 5W4/5W4GT, 5Y3GT, or 5T4 filament

type rectifier for the 5Z4 rectifier tube but you will lose the advantages of soft startup and

low voltage drop offered by the cathode type rectifier. The plate voltages will be reduced

somewhat which will lower the maximum power output. The GZ34/5AR4 cathode type is

also compatible.

12A6

12SJ7 12SC7

heater voltage

heater dc supply

transformer

output transformer

acpower pilot

ac input fuse speaker input level input

power transformer

Appendices _

Specifications

Output transformer wiring diagrams

Replacement parts list

Schematic diagram

MAD Stealth 5 Specifications______

Maximumoutput power into 8 Ωload before clipping: 6 W

Hum and noise output with zero signal in: less than 1 mV(77 dB below 6.5 W)

Input resistance at 1 kHz: 100 kΩ

Output resistance at 1 kHz: less than 0.1 Ω(damping factor greater than 80)

Frequencyresponse (1 Woutput): 12 Hz–20 kHz – 0.5 dB

Frequencyresponse (5 Woutput): 20 Hz–20 kHz –1 dB

Sensitivity for full output: 0.3 Vrms

Power consumption: less than 25 W

Output transformer wiring diagrams______

Normally wired for 8 Ohms.

-10

-5

1 10 100 1000 10000 100000

Frequency (Hz)

loop gain

1 W

5 W

frequency response

Replacement Parts List _

Reference Description Qty.

C1 100uF/16V electrolytic capacitor 1

C2, C4 1uF/250V polypropylene capacitor 2

C3 470pF/630V 1% polypropylene capacitor 1

C5, C6 0.56uF/630V polypropylene capacitor 2

C7 47uF/63V electrolytic capacitor 1

C8 2.2nF/250V 1% polypropylene capacitor 1

D1 Green 10 mA light emitting diode (LED) 1

FU1 2 A/250 V1-1/4" fuse 1

Fuse holder 1

J1 RCA gold plated phono jack 1

J2, J3 Insulated binding posts (red/black) 2

J4 IEC ac receptacle 1

IEC ac line cord 1

P1 100K linear potentiometer 1

R1, R6 9.1K 0.4 W 1% metal film resistor 2

R2 3.57K 0.6 W 1% metal film resistor 1

R3 100 Ohm 0.4 W 1% metal film resistor 1

R4 470K 0.6 W 1% metal film resistor 1

R5, R9, R10 100K 0.6W 1% metal film resistor 3

R7 562K 0.4 W 1% metal film resistor 1

R8 150K 0.6 W 1% metal film resistor 1

R11, R12 280K 0.4W 1% metal film resistor 2

R13 200 Ohm 2W 5% metal oxide resistor 1

R14, R15 866 Ohm 0.4W 1% metal film resistor 2

R16 2.2K 0.5W 5% carbon film resistor 1

R17 1.5K 10 W 5% wire wound resistor 1

R18 7.5K 2 W 5% metal oxide resistor 1

R19 75K 0.5W 5% carbon film resistor 1

R20 1K 0.5W 5% carbon film resistor 1

SW1 SPST rocker switch (ac power) 1

SW2 DPDT slide switch (heater voltage selector) 1

TR1 8000CT:4/8/16 10 W output transformer (Hammond 1608) 1

TR2 560VCT/60mA + 5V/2A power transformer (Hammond 271X) 1

TR3 12VDC/1A ac adaptor 1

V1 12SJ7/6SJ7 vacuum tube 1

V2 12SC7/6SC7 vacuum tube 1

V3, V4 12A6 vacuum tube 2

V5 5Z4 vacuum tube 1

Voltage ratings shown for capacitors and power ratings for resistors are minimum values

for replacement purposes.

Schematic Diagram _

3.57K

100*

100/16

1/250

470K R5

100K

562K*

150K

100K

0.56/630

R11

280K*

R12

280K*

R14

866*

R16

2.2K

2.2n

12SJ7

12SC7

Mapletree Audio Design Stealth 5 Monobloc Power Amplifier

R10

100K

1/250

R13

200/2W A

5Z4

5 VAC

2 A

4C9

33/450

R17

1.5K 10 W

280-0-280 VAC

60 mASW1

FU1

C10

47/350

R19

75K

C11

47/350

+C12

47/250

12A6

31 mA

+262 V

Rev. May 15/03

+264 V

R18

7.5K/2W

R15

866*

10000:8Ω

100K

31 mA

12SC7/6SC7

12A6 12A6

12SJ7/6SJ7

470

+12.8 V

9.1K*

6V12V

47/63

R20

* 0.4 W

TR1

TR2

SW2

TR3

12VDC/1A

6.3VCT/2A winding not

used

+13.2 V

+352 V

+263

BR/Y

9.1K*

+262 V

+332 V +243 V

+332 V

+280 V

+153.4 V

+5.3V

+243 V

All other resistors 0.6 W

unlessnoted

115-125 VAC 60Hz

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