Offered for sale;
Used THD UniValve Amplifier head serial number 0863.
This amp head is in excellent condition, fully functional without issue.
“The new THD UniValve is a Single-Ended Class A amplifier head with a single output tube that can be switched at will among many octalbased power tubes for different tones without re-biasing the amp.
Useable tubes include 6L6, EL34, 6550, KT90, KT88, KT77 and KT66. With the amp in “LoV” setting you can use 6V6 for a total output of 5 watts. A special UniValve Yellow Jacket Converter is available allowing the UniValve to use the popular EL84 power tube at a total of 4 watts output power, also in “LoV” setting.
Likewise, the two preamp tubes can be any combination of 12AX7, 12AT7, 12AU7, 12AY7 or 12AZ7. The UniValve delivers tones from smooth and clear to very aggressive overdrive. It is easily capable of driving a 4 x 12 cabinet, yet is quite small and light. It has a built-in Hot Plate Power Attenuator that allows for full output distortion at almost any volume. And it doesn’t cost as much as you might think.
What is Class A?
Class A is a term given to an amp that runs its tubes at full current all the time, unlike most tube amps that alternate between running one set of tubes and the other set, each for one half of the wave. The set not in use is turned off by a positive swing of the grid voltage. Single-ended output stages always operate in Class A. Most push-pull amplifiers, including the venerated Vox AC-30, operate in Class AB when overdriven, even if they are in Class A while clean. Class A operation has its own unique tonal characteristics that set it apart from other tube amp classes.
Class A amps sound great at low volumes, and even better as you turn them up. Thus, with the relatively low wattage of the UniValve you can turn up the amplifier to take full advantage of its stunning output distortion tone without deafening anyone. Being single-ended, the UniValve has a much fuller harmonic content to its overdrive and distortion because it is rich in both even and odd harmonics. The push-pull configuration that most amplifiers use cancels even harmonics leaving only half of the sonic spectrum offered by the UniValve.”
Controls and Features
The UniValve has two inputs: one for high gain and one for low gain ranges. The low gain input with 12AX7 preamp tubes in the amp gives a wide range of clean sounds from “Country” clean and crisp to Jazz direction warmth. With the controls pegged and a relatively high output humbucker, the low-gain input can deliver a very convincing “Texas Blues” type of overdrive. Plug into the high-gain input and you are in a whole different world from early “British Invasion” tones to contemporary hard rock sounds. The most surprising aspect to the UniValve’s high-gain overdrive is that even with stunning levels of grind, you can still play complex chords and hear every note of the chord clearly. There is none of the mush and confusion normally associated with high-gain tones. The controls are the traditional Volume, Treble and Bass controls along with what we call an “Attitude” control. The Attitude control determines how the driver stage responds to the signal and how it drives the power tube. The Attitude control is not a Presence control, as the amplifier has no negative feedback from the output transformer back into the driver stage.
There is also a built-in THD Hot Plate power attenuator that lets you have full output distortion at any volume level. The Hot Plate has its own hard-bypass switch on the front panel, which completely removes it from the circuit for Full Power playing into a speaker.
The UniValve features a light bulb on the front panel that not only glows when the amplifier is played, but it also provides very effective noise-reduction. For occasions when you do not want this feature, there is an On-Off switch for the light bulb circuit right on the front panel.
The UniValve now has a HiV/LoV switch, which reduces the voltage to the tubes somewhat like a Variac. In the LoV setting, the power is reduced more or less to half, pick attack is slowed and the feel is more “elastic”. The amp also has more “bloom” in the LoV setting and can also take a number of tubes that cannot withstand the higher voltages of the HiV setting. These tubes include the entire 6V6 family and a number of antique 6L6 family tubes like the 6L6G, 6L6GA and 6L6GB.
The UniValve has a GREAT- sounding transformer isolated line out on the back panel complete with an adjustable level control and a switch to choose Line or Instrument-Level signal. The transformer used in the line out was chosen for its pickup-like impedance and tonal characteristics. Most amplifiers’ line outs only work well when used to drive other power amplifiers, and sound harsh and thin when plugged into the guitar input of an amplifier. Not so with the THD UniValve. Even into the input of a Marshall 100-watt head, the UniValve provides a warm, fat, tight and sweet sound that FEELS like an amplifier, not like a preamp-amp rig.
The UniValve can drive any speaker load from 2Ω all the way up to 16Ω. 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 to allow the silent use of the amp for direct recording purposes when miking a cabinet is not practical.”
This is a cool feature packed Class “A” head that was hardly ever played. Why did the previous owner deny himself?
Your turn. Take it from here!
(THD Padded Carry Bag)
“We test every used amp and pedal when we buy it and bring it up to our standards before we offer it for sale. Then we burn it in for an hour or so before we ship so that there are no surprises.”
Weight lbs.: 23 lbs.
Depth in.: 7
Height in.: 9
Rectifier: solid state
Preamp: Pert’near any 12A style you want
2 - 12AX7
1 – 12AX7, 1 12AY7
This one currently has a Mullard 12AT7 and a JJ ECC83
Power: Pert’near any 9 pin style you want
1 - 6L6, 6CA7, KT88, 6550, 6V6
This one currently has a JJ E34L
*Please note: we do our best giving descriptions of used pieces. We have found it impossible to describe every mark on an instrument or amp that is not in the "mint" category. Also, what's important to you may not be important to someone else. For example, you may say, "I don't care what it looks like as long as it plays or sounds well." Another person may say, "Body cosmetics are very important to me so tell me about every scratch, nick and blemish." So, please ask the questions that are most important to you. If you ask they will be answered. They are free and there's no limit. Additional photos can also be made available.
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