Mapletree Super Stealth User manual

Super Stealth
Monobloc Power Amplifier
Users' Manual
Rev. Apr. 29/12
Mapletree Audio Design
Lloyd Peppard
R. R. 1, Seeley's Bay, Ontario, Canada, K0H 2N0
[phone]
[email protected]
http://www.mapletreeaudio.com
© Copyright Lloyd Peppard 2002-12

2
Introduction _
The Mapletree Audio Design Super Stealth Monobloc Vacuum Tube Power Amplifier
provides 8 W of clean output power within a compact chassis and offers a number of
desirable features:
? ? The exclusive use of high quality new old stock (NOS) and current production tubes
that can be obtained at modest cost from many suppliers.
? ? Class AB Ultra-Linear push-pull beam power tetrodes delivering 8 Watts output
power at low distortion.
? ? Wide frequency response: 20 Hz –20 kHz –1 dB at full power output.
? ? Optional input volume control and high sensitivity of 0.45 V permit use without a line
preamp if desired.
? ? DC heater power supply for low noise.
? ? The exclusive use of Nichicon polypropylene film signal capacitors and Nichicon
Musehigh performance electrolytic cathode bypass capacitors.

3
Adjustments____
Level control (optional) –The sensitivity of the Super Stealth is 0.45 V to produce full
power output. For some high-output preamps, it may be advantageous to reduce the input
level in order to shift the preamp volume control nearer the mid-position for normal
listening. The Super Stealths can also be used without a preamp, directly from a source
(e.g. CD player) using the level controls for volume and balance adjustment.
Speaker impedance –The standard wiring is for an 8 Ohm loudspeaker. If 4 or 16
Ohm outputs are required, the wiring will need to be changed under the chassis. The
connection diagram below shows the connections to be made.

4
Specifications___
Tube complement: 12SJ7, 12SC7, 2 x 6V6GT matched pair
Rectifier: solid state with ultra high-speed silicon diodes
Output configuration: Class AB1ultra-linear push-pull with self bias (6V6GT matched
pair recommended)
Phase inverter: cathode-coupled
Heater supply: dc heater voltage for all tubes
Rated power output (8?): 8 W
Frequency response at 2 W output: 20 Hz–20 kHz –0.5 dB
Frequency response at 5 W output: 20 Hz–30 kHz –1 dB
Gain: 25 dB (17.8) or 0.45 V input for 8 W output
Input resistance: 430 k?
Noise: less than 0.7 mV (81 dB below rated output)
Dimensions: 6"W x 11" D x 5" H overall (SE version is 9"W x 13" D x 6" H)
Weight: 10 lb
Power consumption: 70 W, 120-125 VAC 50/60 Hz
Fuse: 3 A fast blow type rated at 250 V (located inside chassis)

5
R2
3.57K
MF
R3
107
MF
C1
47/25
Nichicon
Muse
C2
0.047/400
PP
R4
510K R5
110K
+
R7
510K
R8
4.7K
CC
R9
150K
MF
C5
0.047/400
PP
C6
0.047/400
PP
R11
470K
R12
470K
R14
1K MF
R16
2K
C9
820p mica
V1
12SJ7/12SJ7/GT
C
V2
12SC7
3
5
6
Mapletree Audio Design Super Stealth Monobloc Power Amplifier
R10
150K
MF
1
4
2
R13
240/4W A
B
C10a
50/500
+
SW1
FU1
3A
C11a
50/500
+
C
A
B
R20
110K
C11b
50/500
+C10b
50/500
+
V3
6V6/6V6GT
V4
6V6/6V6GT
+300V
Rev. Apr. 29/12
+345 V
R19
5.1K/2W MO
R15
1K MF
8000:8?/10W
Hammond 1608
1
45
3
8
6
3
4
5
8
3
4
58
C3
270p
mica
1
1
R6
11K
TR1
TR1
J1
J2
J3
J4
+293 V
BL
BR
R
Y
BK
Resistors are 5% 1 W carbon film
unless noted
MF = 1% 0.6 W metal film
CC = 5% 1 W carbon composition
WW = 5% 5 W wire wound
MO = 5% 2 W metal oxide
PP = polypropylene film
120 VAC 50-60 Hz
© Copyright Lloyd Peppard 2004-12
chassis gnd bus
R
R
Y
Y
BK
BK
BL/Y
BR/Y
6V6GTs
2
2
7
7
5 VAC
2 A
8
77
2
12SC712SJ7
D1
LED
+
C12
10000/16
R21
1.8K
BR1
6A
R/Y
R17
3.57K
MF
R18
3.57K
MF
6.3 VAC
3 A
G
GR22
500/10W
D2, D3
MUR180
C4
0.1/400
PP
Hammond 270DX
275-0-275 VAC 90 mA
+2.2 V
+303 V
+292 V +170 V
+18 V
+245 V
+234 V
+76 V
+55 V
13 VDC
+
–
R1
470K
R22
560
240
240
240
240
1K 5W WW
1K 5W WW
C7
220u/40V
+
+2.2 V
Pin 6, V3
Pin 6, V4

6
Tube substitutions______
The Russian-made 6V6GT output tubes supplied are an excellent sounding, high-
reliability design, replaceable at modest cost. However, users may wish to substitute NOS
(new old stock) versions from a variety of manufacturers made over the past 70 years.
The metal 6V6 is also a possible substitute and may offer a different sonic character than
the glass versions. Matched pairs are recommended.
The 12SJ7 is a pentode developed for audio and low frequency RF circuits and exhibits
very low noise. It rivals the EF86 in most respects. It is also available in glass as the
12SJ7GT. The 12SC7 is electrically equivalent to a 12SL7GT but with a common
cathode shared by the two triodes. It is especially well suited to the phase splitter role in
the Super Stealth. There is no substitute for this tube nor is there a glass version.
Super Stealth
tube layout