VHT Special 12-20 RT Head User Manual
VHT SPECIAL 12/20RT
12-20 Watt Hand-Wired Vacuum Tube Guitar Amplier
User Manual
IMPORTANT SAFETY INSTRUCTIONS
1) Read these instructions.
2) Keep these instructions.
3) Heed all warnings.
4) Follow all instructions.
5) Do not use this amplifier near water.
6) Clean only with dry cloth.
7) Do not block any ventilation openings. Install in accordance with the manufacturer’s instructions.
8) Do not install near any heat sources such as radiators, heat registers, stoves, or other apparatus (including amplifiers)
that produce heat.
9) Do not defeat the safety purpose of the polarized or grounding-type plug. A polarized plug has two blades with one
wider than the other. A grounding type plug has two blades and a third grounding prong. The wide blade or the third prong
are provided for your safety. If the provided plug does not fit into your outlet, consult an electrician for replacement of the
obsolete outlet.
10) Protect the power cord from being walked on or pinched particularly at plugs, convenience receptacles, and the point
where they exit from the amplifier.
12) Unplug this amplifier during lightning storms or when unused for long periods of time.
13) Refer all servicing to qualified service personnel. Servicing is required when the amplifier has been damaged in any way,
such as power-supply cord or plug is damaged, liquid has been spilled or objects have fallen into the amplifier, the amplifier
has been exposed to rain or moisture, does not operate normally, or has been dropped.
14) The amplifier shall not be exposed to dripping or splashing and no objects filled with liquids, shall be placed on the
amplifier.
15) This amplifier shall be connected to a mains socket outlet with a protective earthing/ground connection.
16) The mains/power plug or amplifier coupler is the disconnect device which must remain readily operable.
WARNING: To reduce the risk of fire or electric shock, do not expose this amplifier to rain or moisture.
TABLE OF CONTENTS
OVERVIEW....................................................1
FEATURES.....................................................2
CONTROL PANEL FUNCTIONS.....................3-4
REAR PANEL FUNCTIONS.............................5-6
TONE CONTROL GRAPHS.............................7-8
DEPTH CONTROL GRAPH...............................9
TEXTURE SWITCH GRAPH............................10
FX RETURN - DEPTH CONTROL GRAPH.........11
FX RETURN -TEXTURE SWITCH GRAPH........12
BOOST CONTROL GRAPH...............................13
BLOCK DIAGRAM..........................................14
SCHEMATIC..................................................15
TECHNICAL SPECIFICATIONS......................16
VHT SPECIAL 12/20RT
THE PEDAL-FRIENDLY AMP WITH SELECTABLE POWER RANGES
PLUS ALL-TUBE SPRING REVERB AND TREMOLO
The VHT Special 12/20RT adds tube-driven spring reverb and tube tremolo to the pedal-friendly Special 12/20 platform. Like
the Special 12/20, the 12/20RT features a unique preamp specically designed to excel with pedals and multi-effects units,
with a pedal-friendly all-tube buffered effects loop with send and return level controls. And like the 12/20, the 12/20RT also
accepts a wide range of output tube types, with two power ranges complemented by an adjustable Watts control and a Pentode/Triode switch. The Special 12/20RT also features VHT’s unique Depth and Texture controls, a convenient built-in 9-volt
DC pedal power supply, and an international mains voltage selector switch.
Like the Special 12/20, the Special 12/20RT’s preamp was designed to bring the most out of every effects pedal and multieffects unit with enhanced clarity, detail, and controlled tube compression. Its low-impedance buffered effects-loop send can
effortlessly drive the most difcult pedals without tone or signal loss. Thanks to its variable send and return level controls,
the 12/20RT’s effects loop can accommodate a wide range of pedal, multi-effects units and rack effects. The 12/20RT’s Reverb, Tremolo, Depth and Texture controls are post effects loop, so multi-effects users can plug directly into the effect return
and still benet from the post-effects tube reverb and tremolo, while also ne-tuning the output stage characteristics with
the Depth and Texture controls.
To optimize the amp for a wide variety of output tubes, the VHT Special 12/20RT offers two output-power ranges; safely
located behind the rear panel, a special voltage range switch provides the proper voltages for 6V6 or EL84 output tubes (in
12-watt low-voltage/low-power mode). The high voltage 20-watt setting provides the ideal voltages for higher-power 6L6
or EL34 output tubes. The Special 12/20RT ships with a pair of 6V6 output tubes (VHT 6V6-to-EL84 socket adapters are
required for operation with EL84 tubes). In addition, the Special 12/20RT’s variable Watts control can reduce the maximum
output power to less than one watt for whisper-quiet volume levels.
VHT SPECIAL 12/20RT FEATURES
Special Pedal-Friendly Preamp Design
Tube-Driven Effects Loop with Line Out Jack
Effects Send and Return Level Controls
9-Volt DC Pedal Power Supply
6V6 Tube-Driven Spring Reverb with Deep Switch
Tube Tremolo with Slow/Fast Range Switch
Switchable 12/20 Max Output
Variable Watts Control
Pentode/Triode Switch
6-Position Depth Control
3-Position Texture Switch
Footswitchable Push/Pull Boost
Switchable 4, 8 or 16 Ohm Speaker Outputs
International Voltage Switch
Four 12AX7 Tubes
One 6V6 Reverb Driver Tube
Two 6V6 Output Tubes
Accepts EL84 Output Tubes*
Also accepts 6L6 or EL34 Output Tubes
Mod-Friendly Handwired Eyelet-Board Construction
2-Button Reverb/Tremolo Footswitch (Included)
1-Button Boost Footswitch (Included)
12” VHT ChromeBack Speaker, 60-watt, 16 ohm (Combo Only)
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VHT — THE WORLD LEADER IN AFFORDABLE HANDWIRED AMPLIFICATION
*With VHT 6V6-to-EL84 Socket Adapters
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CONTROL PANEL FEATURES
6 8
SLOW/FAST
DEEP
1 2
3 4
5
7
9 14
10
11
12 13
1. Power Switch: This switch turns the amplier on or off.
2. Pentode/Standby/Triode: The Triode setting reduces the amplier’s maximum output power to approximately one-half
of the Pentode setting. Triode setting produces a richer and smoother tone, with earlier breakup than the Pentode setting.
The middle position is Standby mode.
3. Watts Control: The Watts control adjusts the output tube’s operating voltage and maximum output power. Maximum
output power ranges from less-than 1 watt (fully counterclockwise) to 12 or 20 watts (fully clockwise).
4. Jewel Light: This light will be illuminated when the Power Switch is in the On position; the jewel light will be off when
the Power switch is in the Off position.
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CONTROL PANEL FEATURES CONTINUED
5. Depth Control: This 6-position rotary switch selects the output tubes’ low-frequency roll-off point. Set fully clockwise for
the deepest low-frequency extension. Lower settings (counterclockwise) expose more midrange texture and detail; the lowest settings emphasize more presence and bite.
6. Texture Switch: This 3-position rocker switch selects the output’s high-frequency roll-off point and also inuences the
midrange texture. The middle position provides maximum top-end extension and the most harmonically complex texture;
the left position provides subtle high-frequency roll-off for a slightly smoother texture; the right position rolls-off more high
frequencies for the smoothest texture.
7. Tremolo: This control adjusts the intensity and depth of the tremolo effect. The Tremolo can be switched on or off with
the 2-button Reverb/Tremolo footswitch.
8. Slow/Fast Switch: This switch selects the tremolo circuit’s range.
9. Speed: This control selects the tremolo speed.
10. Reverb: This control adjusts the intensity of the Reverb effect. The Reverb can be switched on or off with the 2-button
Reverb/Tremolo footswitch.
11. Pull Deep: Pull this knob to add more low-end depth to the reverb signal.
12. Tone Control: This control adjusts the balance of the high and low frequencies.
13. Volume Control: Turning this knob clockwise increases the preamp drive and overall sound level.
14. Pull Boost: Pull this knob to partially bypass the internal tone shaping/voicing circuitry, which boosts the preamp gain
and increases the midrange emphasis. This feature can also be accessed by the footswitch.
15. Input: Pedal-friendly 1-megohm input impedance.
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