THD Flexi 50 All Tube amp Made in USA amplifier head discontinued product

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About This Listing

THD Flexi 50

All Tube amp

Made in USA

discontinued product

Top Quality fantastic sound

 Perfect Working

Excellent condition with low usage.

From the manufacturer:

The 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 preamp and power tubes in any combination, including 6L6, EL-34, 6V6, 6CA7, 8417, 6550, KT-66, KT-77, KT-88, KT-90, KT-100, EL-84 (with Yellow Jacket adaptor), 6K6, 6F6, 12AX7, 12AY7, 12AU7, 12AT7, 12AZ7, 12DW7, 12BH7, ECC-83, ECC-82, ECC-81 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 amp still demonstrates dramatic touch sensitivity, cleaning up very well when the volume on the guitar is reduced. Additional 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 dual bias controls permit the user to correctly bias even mismatched tubes, eliminating the need for matched power tubes and a trip to the tech when changing tubes.

The unique combination of our touch-sensitive input circuit and the wonderfully active and reactive tone control section (that we slaved a year to perfect) make for a front-end that really responds to subtle and not-so-subtle changes in the signal being fed into the amplifier either by the guitar or any effect that may be between the guitar and the amplifier.

  • English Overdrive California Clean. Texas Punch.
  • "If you’re a tone tweaker with a good assortment of tubes, you’ll have a blast experimenting with more unusual tube types and combinations in the quest to find a personalized sound that’s as unique and fresh as the Flexi-50’s design. This is an outstanding amp, and it wins an Editors’ Pick Award." - Guitar Player Magazine
  • This is the standard "cage head" version, complete with a perforated steel cage to protect the tubes while providing ample ventilation.
  • "The tone is simply breathtaking, and for evoking the likes of Kossoff, SRV and Rory Gallagher or Hendrix, it's probably close as you'll get without reincarnation." - Guitarist Magazine
  • Hand-built in Seattle, WA.

Also have an analog speaker simulator that I will be listing by SPL. Perfect with this head for live performances.

Product Description

THD Flexi-50W Amp Head

English Overdrive.
California Clean.
Texas Punch.

These three phrases probably best sum up the THD Flexi-50 tones……..

What does all of this mean for you, the player? It could very well mean that the search for your sound is finally over. While the UniValve 15W and BiValve-30 amplifiers offer the same flexibility and choice of tubes, they do so in a Class-A circuit. While Class-A amplifiers do have a strong following due to their smooth, even character, there are many players who need, or even crave the immediacy, clarity and "punch" of a grid-biased Class-AB amplifier. The 40 year love affair that guitarists have had with the now almost cliché 50 watt rock amp head is proof of this.

In the Flexi-50, THD have brought together an ideal combination of simplicity and flexibility, hence the name "Flexi-50". Why strive for simplicity? Robust design and construction are among the reasons. Ease of use is another prime reason. Often guitarists who have purchased 3 or 4 channel guitar amplifiers discover that aside from varying gain levels, all channels unfortunately sound and feel more or less the same, dashing their dreams of flexibility. Another by-product of an overly-complex amplifier is that it can take a very long time to uncover a sound that really works for you.

How is the Flexi-50 different? Firstly, it’s a single-channel amplifier, but one that can be switched and blended among a number of different sounding and different feeling voices. These changes can come from a number of methods. One is the foot-switched preset boost, with its own dedicated tone control that allows you to make your boosted sound darker than the clean sound, brighter, or anywhere in between. Couple that with the foot-switched Master Volume, with it’s tone ‘cut’ control, the Hi/Lo guitar input, the bright switch, the 50/20 power switch and the sound palette becomes endless……

The unique combination of the touch-sensitive input circuit and the wonderfully active and reactive tone control section (that THD slaved for a year to perfect) make for a front-end that really responds to subtle and not-so-subtle changes in the signal being fed into the amplifier either by the guitar, or any effect that may be between the guitar and the amp. Back off on the guitar’s volume, and the amp ‘cleans up’ without losing the fatness of the full-volume sound.

Switch from an over-wound bridge pickup to a clearer, lower-output neck pickup and suddenly the amplifier responds very differently. Our input is quite sensitive to the individual impedance curves and inductance characteristics of your pickups, so you will not experience the all-too-common situation where every guitar you own sounds the same through your amp. PAFs sound like PAFs. Strats sound like Strats. Filtertrons sound like Filtertrons. Lipstick pickups sound like, well, like nothing else on the planet. You’re into exotic handmade guitars and pickups? Wouldn't it be nice to have an amplifier that lets you hear the difference between 9000 turns and 9200 turns of wire in a pickup? Come plug in and see (and hear) for yourself.

Or…. you like to use pedals? There are many talented pedal makers coming out of the woodwork from all corners of the world. The THD Flexi-50 has no trouble helping you hear the difference between a NOS military-grade germanium transistor and a modern equivalent. You decide if they are equivalent or not, and with the Flexi-50, you will have the tool to do so. Does it like pedals? It LOVES them.

More about the overdrive capability of the Flexi-50... With its modified-design, custom-tuned post-phase-inverter master volume circuit, the Flexi-50 can give you a luscious palette of overdrive sounds before you even get the output stage working, and these sounds are all highly touch-sensitive as well.

Switching tubes is easier than ever before. With the built-in bias adjustments, you can easily and accurately set the bias in about 20 seconds, even with two completely different tubes.

Other features include a line-level effects loop, and a 50-watt to 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. The Flexi-50 also has a series/parallel switched impedance selector, that can take any extension cab from 2 to 16 ohms impedance, always using 100% of the transformer windings all of the time, which is 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.


I want you to be 100% satisfied with your purchase, please contact me if you are not before leaving any feedback! Items can be returned within 30 days for a refund of the sale price. The customer is responsible for return shipping charges. Returns are inspected upon arrival to confirm condition.

I care about shipping and the item will be professionaly packed and shipped. I pack everything securely, with lots of packing material. It will be double boxed with plenty of bubble wrap.

Please email me if you have any questions or want more pictures.

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Product Specs

Listed4 years 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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