THD Uni Valve (More Recent Images Coming)

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Charles 's Gear Locker
Jacksonville, FL, United States
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About This Listing

Tube-swap your way to a whole new tonal territory.


TYPE: All valve single- ended amp head OUTPUT: Nominal 15 watts RMS

VALVES: Choice of single EL34, 6L6, 5881, KT88, 6550, 5881, 6V6 and EL84 power valves; two ECC81, 2 or 3 in preamp.

I will include at no added cost to the buyer a small box of tubes and the EL 84 Yellow Jacket Adapter that I acquired for this amp at a cost of more than $100.00..

DIMENSIONS: 190 (h) x 390(w)x230mm(d) 

WEIGHT (kg/lb): 8/18 CABINET: Powder coated steel

CHANNELS: One CONTROLS: Volume, bass, treble, attitude, Hotplate level, Hotplate in/out, hi/lo voltage, noise reduction in/out, line out level and instrument/line switch

ADDITIONAL FEATURES: Multiple valve choice with no rebiasing, Hotplate power attenuator, noise reduction circuit, transformer-isolated vari-level line out

The THD UniValve 15W Class A Amplifier Head delivers tones from smooth and clear to warm and full to aggressive overdrive. The single-ended Class A circuit design uses the highest-quality parts and hand-built construction for clean and faultless operation.

The single output tube can be switched at will with nearly any octal-based power tube for different tones without re-biasing the amp, and the 2 preamp tubes can be switched for any combination of 12AX7, 12AT7, 12AU7, 12AY7, or 12AZ7 tubes.

The UniValve is easily capable of driving a 4x12" cabinet, yet is also small and light. Its built-in Hot Plate Power Attenuator lets you experience the indescribable freedom of wailing away with full output distortion at volume levels that are quiet enough to let your neighbors sleep.

There are 2 inputs”one for high gain and one for low gain. With 12AX7 preamp tubes, the low gain input gives a wide range of sounds from Nashville clean and crisp to Memphis down and dirty. With the controls pegged and a relatively high-output humbucker, the low-gain input delivers a tantalizing Texas blues overdrive. Plug into the high-gain input for a whole new world”from early British Invasion tones to modern high-gain metal attack”but with none of the mush and confusion normally associated with high-gain tones.

The controls include the traditional Volume, Treble, and Bass along with an Attitude control knob that determines how the driver stage responds to signal and how it drives the power tube. There are also controls for the Hot Plate, including a hard-bypass switch. The noise reduction circuit in the Hot Plate features a light bulb fixture on the front panel that glows when you play. There is an On-Off switch for the light bulb.

On the back panel the UniValve has a transformer-isolated line out with an adjustable level control and a switch to choose line-level or instrument-level signal. The speaker outs on the UniValve can drive any speaker load from 2 ohms all the way up to 16 ohms. When there is no speaker plugged into the speaker jack, the amp uses its own built-in dummy load so no damage will occur, and it's also awesome for direct recording.

  • 15W Class A amplifier
  • Single-ended Class A circuit
  • Handbuilt
  • Accepts almost any power tubes in any combination
  • Ships with 2 - 12AX7s (preamp) and a single EL34 (power amp)
  • 2 preamp tubes can be any combination of 12AX7, 12AT7, 12AU7, 12AY7, or 12AZ7 tubes
  • 2 inputs: one for high gain and one for low gain
  • Volume, Treble, Bass, and Attitude knobs
  • Built-in Hot Plate output attenuator
  • Volume, Treble, and Bass controls
  • Attitude control knob
  • Hard-bypass switch for Hot Plate
  • Light bulb noise-reduction circuit
  • On-Off switch for light bulb circuit
  • Transformer-isolated line out with adjustable level control
  • Choose Line-Level or Instrument-Level signal
  • 2 ohms to 16 ohms speaker load
  • Built-in dummy load
NO CABINET WITH THIS SALE.  I have a 112 Mesa Boogie Wide Body that works great with it, if interested.

UniValve Controls Front Panel
1. ROCK Input: This jack fits a standard 1/4" mono shielded instrument cable. If you use a stereo cable, the sleeve signal will be ignored. Do not use speaker cable into this input. The ROCK input is the high gain input, meaning that both preamp gain stages will be engaged in order to pass the hottest possible signal to the power section.
2. ROLL Input: This jack fits a standard 1/4" mono shielded instrument cable. If you use a stereo cable, the sleeve signal will be ignored. Do not use speaker cable into this input. The ROLL input is the low gain input, meaning that the first preamp gain stage will be bypassed.
NOTE: You cannot plug into both inputs simultaneously or otherwise A/B between inputs. Plugging into the Roll input will disable the Rock input.
3. Volume: This knob controls the loudness of the amplifier. The higher the volume knob setting, the more the tubes are engaged.
4. Treble: This knob can be used to boost or cut the high frequency response of the UniValve.
5. Bass: This knob can be used to boost or cut the bass frequency response of the UniValve.
6. Attitude: The attitude knob determines how the driver tube responds to the signal, and how it drives the power tube. If the Attitude knob is turned up, the UniValve will sound edgier and more aggressive. With the Attitude knob turned down, the UniValve sounds sweeter and more controlled.
7. Light Bulb ON/OFF Switch: The light bulb is part of the noise reduction system of the amplifier. When the light bulb is turned on, the noise reduction circuit is enabled. When turned off, the noise reduction circuit is disabled. The light bulb is powered by the signal coming from your guitar. Thus when you stop playing, the light bulb will stop glowing. If the light bulb does not glow even when it is switched on and you are playing, the bulb may need to be replaced. The amplifier will still function, but the noise reduction system cannot work if the light bulb is blown. Simply unscrew the lens and replace with a #1816 bulb only. These bulbs are available through any THD dealer or directly from THD. They can also be found at most electronic supply houses.
8. HOT PLATE Attenuator Control: The UniValve does not have a master volume control typical of many guitar amplifiers. Instead, the UniValve is a non-master volume amp with built-in attenuation. The advantage to this is that you can achieve true power tube saturation, and then utilize the built-in THD Hot Plate power attenuator to have full output distortion at any volume level. The Attenuator control determines the amount of attenuation applied. Turn the control all the way clock-wise and you will be attenuating by about 3-4 dB. As you turn the control counter clockwise, the volume drops smoothly down to almost no sound. This control is only activated when the Full Power / Attenuator switch is set to Attenuator.
9. FULL POWER/ATTENUATOR Switch: When set to Full Power, the Hot Plate is completely removed from the circuit for Full Power playing into a speaker. When set to Attenuator, the Hot Plate is placed in the signal path after the power section and the Hot Plate Attenuator Control above is activated. The Standby switch should be in the standby position when switching between the Full Power and Attenuator settings.
10. HI V/LO V Switch: This switch determines the plate voltage of the power tube. At the Hi V setting, depending on which power tube you use, approximately 450 to 470 volts are applied to the plates (a tube that draws more current will have a lower plate voltage). The amp has twice as much power at this setting than it does at the Lo V setting and results in a sound that is punchier, more aggressive and more “in your face.” At the Lo V setting, depending on which power tube you use, approximately 300 to 320 volts are applied to the plates. This setting will give you a sweet, warm and smoother sound with a slower attack. To insure maximum tube life, the standby switch should be in the standby position when switching between the Hi V and LowV settings.
11. Standby Switch: Standby mode keeps the power tubes powered and the amplifier itself off. Always power up in Standby mode and allow the tubes to heat up for at least two minutes before switching to Play. The amp should also be placed in Standby before it is turned off to cool the tubes more gradually and to reduce the possibility of internal arcing.
12. Power On/Off: The Power switch turns the amplifier on or off.


This item is sold As-Described

This item is sold As-Described and cannot be returned unless it arrives in a condition different from how it was described or photographed. Items must be returned in original, as-shipped condition with all original packaging.

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Product Specs

Listed2 months ago
ConditionExcellent (Used)
Excellent items are almost entirely free from blemishes and other visual defects and have been played or used with the utmost care.learn more
Made In
  • United States

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