We love the sound of THD AMPS, particularly the new THD Flexi-50 amplifier head. THD’s Flexi-50 is a precision hand-built 50-watt Class-AB amplifier with foot-switchable overdrive/boost, foot-switchable master volume control and the ability to use almost any pre amp and power tubes in any combination, including 6L6, EL34, 6V6, 6CA7, 8417, 6550, KT66, KT77, KT88, KT90, KT100, EL84 (with Yellow Jacket adaptor), 6K6, 6F6, 12AX7, 12AY7, 12AU7, 12AT7, 12AZ7, 12DW7, 12BH7, ECC83, ECC82, ECC81 and many more, giving the user a huge pallet of available sounds simply by changing tubes. The amplifier has a fat, clear, full clean sound reminiscent of late 1950s to early 1960s American combos, and overdrive to rival the best British heads. Even at the highest overdrive settings, the THD Flexi-50 amp still demonstrates dramatic touch sensitivity, cleaning up very well when the volume on the guitar is reduced. Additional Flexi-50 amp features include external bias test points and individual bias controls, permitting the user to quickly and accurately set the output tube bias with any digital voltmeter.

The Flexi-50 has dual bias controls which permit the user to correctly bias even mismatched tubes, eliminating the need for matched power tubes. Other features include a line-level effects loop and a 50-watt/20-watt switch right on the front panel, letting you drop the plate voltage on the power tubes from 475 to 325, giving not only lower output, but also smoother, more even response and even longer tube life. We also have a series/parallel switched impedance selector that can take any cabinet from 2 ohms to 16 ohms impedance, and always uses 100% of the transformer windings all of the time, another THD innovation. This assures you a full, even output sound, regardless of the impedance setting. The power and output transformers are fully shielded to assure that hum and noise are kept to an absolute minimum, and that pickup-feedback from transformer coupling is all but eliminated.

THD Bi-Valve Amp

THD Bi-Valve Like the UniValve, the Bi-Valve is a single-ended pure Class A design. However, it has two output valves which are wired in parallel and combined through a special output transformer to deliver up to around 30 watts. You can use almost any output valve you like without touching any kind of bias adjustment, and get this: in the Bi-Valve you can use them in any combination as well. Combined with the capability to take almost any pre amp valve, this makes the THD bi-valve even more of an amp-tweak ers dream than its predecessor. Because there's such a wide range of tone available you your style. The bi-valve sits in the same compact pressed steel chassis as the UniValve and, except for the extra valve and control plate, it looks almost identical. The UniValve's acid-etched control plate was inspired by Glasgow artist Charles Rennie Mackintosh; this time round THD have gone for a marine theme, with an intricate diamond scale design. When it comes to describing the Bi-Valve's sounds, it's difficult to know where to start, or when to stop, for that matter. You can use almost any power and preamp valve combination under the sun, and as a result the tonal range is virtually unlimited.

The THD Bi-Valve has cleaner tones. and a rich, sonorous detailed mid-range that will flatter any guitar, with a bell-like treble that almost sounds like a chorus effect. Low-end response through a ported cab containing a pair of Celestion Vintage 30 speakers is full without becoming too tubby. Using the volume control in conjunction with the two inputs you can cover the whole gain spectrum, from squeaky clean to absolute brain frying power-amp distortion with almost infinite sustain, and all the time the bi-valve stays totally musical. Even at full-tilt you can still pick out each string within a chord, and the tone controls seem to have just the right range, whatever valves are in use. The smaller valve works to balance out the EL34's hollow midrange and aggressive distortion with a unique high-end response - somewhere between the best vintage Marshall and tweed Fenders, with a hint of AC30 thrown in.   The THD Bi-Valve is a great amp !

The THD Uni-Valve Amp

THD Hot Plate

The THD Hot Plate - A power attenuator is a device placed between the speaker output and the speaker cabinet. It acts like a huge master volume control and permits the amp to be turned up most or all the way while absorbing most of the power generated by the amplifier and turning this power into heat. The THD Hot Plate passes a small part of the power to the speaker. Musicians use attenuators because their amps sound good at high volumes, especially with full distortion, but in rehearsal, small clubs, or at home, they can't turn the amp up. They are also used in recording studios for better separation between the instruments, and for use when the speaker sounds best at low levels, or if it can't handle the power output. The Hot Plate also makes a perfect dummy load.

THD needed a good attenuator for our in-house testing of THD amplifiers. The amps had to be tested at all volumes, clean and pure to wild distortion, and they were tired of their ears. They tried all the attenuators on the market, but they muffled the sound and made even THD amps sound dull. Now THD design engineers don't have to worry as much about hearing loss, and with the Hot Plate neither do you.

THD Yellow Jacket

The THD Yellow Jacket - What are Yellow Jackets® ? Yellow Jackets Converters are a type of specialized adapters which permit the use of EL84/6BQ5 power tubes in place of 6V6, 6L6, EL34, and 7591 types. They give you simple Class-A operation from any amp. Yellow Jacket Converters not only rearrange the pin locations of the tubes, but also provide the necessary current limiting on the screens and cathode as well as blocking the amplifier's grid bias voltage, while configuring the EL84 in a Class-A, Self-adjusting cathode-bias circuit. In other words, there are no adjustments to make and no modifications necessary, you simply plug the Yellow Jackets into the amp's output tube sockets, (in cathode-bias amplifiers) screw the ground wires under one of the output tube socket mounting screws, plug the provided EL84's into the Yellow Jackets, turn on the amp and play.

It's like getting a whole new amplifier! In Champ and Deluxe type amplifiers, the Yellow Jackets output is smooth, strong and more even than with the stock 6V6s. When the Yellow Jackets Converters are installed in larger amplifiers intended for 6L6s or EL34 output tubes, the high plate and screen voltages are reduced as well as current limited to protect the EL84 and to drop output power. When a pair of Yellow Jackets are used in a Marshall 50 watt or similar amplifier, the overall power drops to about 20 watts and takes on more of the character of an old Vox AC30. The distortion is smoother and more even and the output is both substantially reduced and more compressed due to the Class-A nature of the Yellow Jackets. In a 100 watt amp like a Twin Reverb or Marshall 100, either two or four Yellow Jackets can be used. If only two are used and the other two sockets are left empty, the output is dropped to about 20 watts. With four in place, the amp puts out about 40 watts and takes on a whole new warmth and richness.

In the cases of the YJ7591 converters, the overall output power remains the same, but the sound becomes fuller and the extinct 7591 are replaced with common and inexpensive EL84 tubes. In old Ampeg Reverb Rockets and the like, you experience a warmth and sweetness that you could never get with the now unavailable 7591 tubes.