Mapletree Super Stealth + User manual

Super Stealth +
Monobloc Power Amplifier
Users' Manual
Rev. Mar 25, 2019
Mapletree Audio Design
Lloyd Peppard
R. R. 1, Seeley's ay, Ontario, Canada, K0H 2N0
[phone]
[email protected]
http://www.mapletreeaudio.com
© Copyright Lloyd Peppard 2015-19

Introduction _
The Mapletree Audio Design Super Stealth + Monobloc Vacuum Tube Power Amplifier
provides 30 W of clean output power within a compact chassis. It 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 A Ultra-Linear push-pull beam power tetrodes delivering 30 Watts output
power at low distortion.
Wide frequency response: 20 Hz – 20 kHz -1 d at full power output.
Self biased output tubes—no adjustments required.
The exclusive use of Nichicon polypropylene film signal capacitors and Nichicon
Muse high performance electrolytic cathode bypass capacitors.
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Powering Up_______
Please read this instruction manual thoroughly before powering up your Super Stealth +
amplifiers for the first time. The location of the tubes is shown below. When installing
tubes, locate the key on the central spigot and make sure it matches with the indent on the
tube socket. Push the tube into the socket with a slight rocking motion to ensure it seats
properly. Removal is also easier of the tube is rocked slightly as it is pulled out. Don’t
over-do the rocking as it can cause the spigot to break off. The EL34 output tubes are
installed as matched pairs as indicated on the boxes supplied with your amplifier.
Matched quads are not required for two monoblocs.
With the tubes installed, connect the IEC power cord to the AC input receptacle on the
rear of the chassis. A proper sized fuse (3 A/250 V fast blow type) has been installed in
the ac socket drawer. Plug the cord into an ac outlet rated for at least 200 W (110-125
VAC, 50-60 Hz). The ac power switch is on the front panel. The pilot light indicates the
AC power is on. You will see the heaters light up, particularly in the EL34 tubes. It takes
approximately 60 sec for the plate voltage to settle to the operational level and stabilize.
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The Super Stealth + is designed to run the EL34 output tubes in self biasing mode
(cathode bias), so no bias adjustments are required when changing tubes or powering up
for the first time. The combined screen and plate current is around 58 mA per tube with a
plate voltage of around 380 V. This results in a total dissipation of 21 W, well within the
specifications of the EL34.
Input/Output connections______
The input RCA jack is located on the rear apron of the chassis. The input resistance is
100 k.
inding posts for connection to a speaker system are located on the rear apron of the
chassis and are appropriately labeled. Speaker interconnect wires can be terminated as
bare wire, spade lugs, or banana plugs. The latter are most convenient, especially if
different speaker systems are to be connected from time to time. The output speaker
impedance is wired for 8 Ohms but can be re-wired easily if required.
Tube substitution____
Matched pairs of currently made EL34s are easily obtained at moderate cost. The
Russian-made EL34s supplied are an excellent sounding, high-reliability design.
However, users may wish to substitute NOS (new old stock) versions from a variety of
manufacturers made over the past 50 years. NOS EL34s should be matched (dc) within
5%.
The 6SJ7 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
6SJ7GT. The 6SL7GT supplied is a currently manufactured type but NOS versions are
available.
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Specifications___
Tube complement: 6SJ7/6SJ7GT, 6SL7, 2 x EL34 matched pair
Rectifier: solid state with ultra high-speed silicon diodes
Output configuration: Class A 1 ultra-linear push-pull with self bias (EL34 matched pair
recommended)
Driver circuit topology: Mullard type with pentode voltage amplifier (6SJ7) and cathode-
coupled phase inverter (6SL7)
Rated power output (8): 30 W
Frequency response at 1 W output: 20 Hz–20 kHz –0.5 d
Gain: 27 d (22.2) or 0.7 V input for 30 W output
Input resistance: 100 k
Output resistance: < 1
Noise: < 0.7 mV (87 d below rated output)
Dimensions: 8"W x 12" D x 6" H overall
Weight: 15 lb
Power consumption: 100 W, 120-125 VAC 50/60 Hz
Fuse: 3 A fast blow type rated at 250 V
1 kHz sinewave at 32 W output
into 8load (16 V rms)
10 kHz square wave at 10 V p-p
output into 8 load
requency response at 1 W
output into 8
5
-4
-3
-2
-1
0
1
10 100 1000 10000 100000
frequency (Hz)
dB

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Warrant
Your Mapletree product is warranted against failure due to materials, components, and
workmanship for 2 years from the date of shipment. This warranty is not transferable
without agreement from Mapletree Audio Design. Tubes are warranted against failure for
90 days. This warranty is not inclusive of shipping costs.
Care of our Amplifier
Heat is the enemy of the components in your amplifier, particularly the capacitors.
Ensure that there is adequate space for air to circulate over the top of the amplifier. Heat
rises, so it is not advisable to place heat sensitive components on a shelf directly above a
tube amplifier.
The painted surfaces of your amplifier are finished in baked lacquer. The finish hardens
with age due to heat and becomes quite scratch resistant. However, hardness does not
prevent chipping of the surface. It is possible to touch up small chips with spray lacquer
applied with a fine brush so a drop of paint fills in the chip. Consult Mapletree Audio
Design for the automotive paint color for your unit.
Do not attempt to clean the painted surface or labels of your unit with any liquid other
than water applied with a slightly damp cloth. Dust is best removed using a soft 1”
paintbrush.
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