Saturday January 14, 2012

THD UniValve

THD Electronics are known mostly for their Hot Plate Power Attenuator. However, dig a little deeper and the company has an impressive line of small portable amps. Recently THD lent some tech and experience to Jet City Amplification in the form of the Jet City PicoValve. We’ll take a closer look at the original amp this was based on – the THD UniValve.

The THD UniValve is a 15 watt single ended Class A amplifier head that is a compact, low-wattage tone machine. The distinctive perforated steel cage and innovative components is the brain child of Andy Marshall, THD’s founder and designer. The UniValve is packed with technology not found elsewhere.

The THD UniValve’s unique selling point is the swappable octal based power or preamp tubes without the need to re-biase the amp. You can easily substitute 6L6, EL34, 6550, KT90, KT88, KT77 and KT66 or combine them with any variety of 12AX7, 12AT7, 12AU7, 12AY7 or 12AZ7 tubes for different tones. UniValve’s unique circuitry determines the correct bias voltage of the output tube regardless of type or tube wear. The self biasing feature not only saves a lot of time and hassle visiting a technician but cash too. Money that could easily be spent on more gear! The other rabbit out of the hat is the UniValve’s built in THD Hot Plate Power Attenuator (which can be bypassed) allowing for some massive distortion at any volume level.

THD UniValve

THD UniValve

On the front panel there are two input jacks – one for low gain and the other for, you guessed it, high gain. The low gain input puts the amp mode into friendly cleans, versatile enough for country and jazz. Add a little break up for some fat Texas Blues and there will be no need for an Ibanez Tube Screamer. The high gain input opens up the amp to some tight vintage Brit rock. Crank it up and the UniValve delivers some screaming overdrive, heavy chug and distortion crunch. This is one of the few portable tube amp heads that is versatile enough to do Metal out of the box. Luckily the Hot Plate is there if you need it.

Standard controls include volume, treble and bass knobs. But exclusive to this amp is an “Attitude” control. THD describes the Attitude control as not a Presence control but how the driver stage responds to signal and load it drives the power tube. An isolated line out at the rear panel with an adjustable line level or instrument level lets the UniValve play nice with other amps or a mixing desk. The rear output 2 ohms to 16 ohms speaker jack allows the THD UniValve to drive any cabinet from a 1x12” to 4x12”. Even the front red light bulb serves a purpose as a noise reduction circuit which also can be switched on or off.

The THD UniValve amp head is a compact box of tricks that delivers Jazz through to Metal tones. The built in THD Hot Plate Power Attenuator and self biasing feature could even save you money in the long run. The THD UniValve amp head retails for $995.95, it is not available as a combo.

THD UniValve 15W Class A Amplifier Head Features:

  • 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

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