THD Flexi 50 Head

No idea what year this amp was made, bought new however.
1-channel, but the boost & master features make it seem like 2.
FX loop is eries: quiet & effective.
Biasing is really something, and the ability to use various /different tubes is great. 50/20 watt adjustability makes it great for studio, rehearsal, or stage. It morphs most amp sounds plus has it's own dynamic & touch-sensitive abilities.

Works well with single coils or HB's, and any style of playing.
Absolutely quiet, but if you load the front end with pedals or chains of stuff, you will hear anything unless you buffer them.
From twang to smooth to bluesy to screwam: it covers the gamut.
Also chimes quite nicely!

Like a tank it is - bottom line.

Have felt the need to contact them, but they have a superb rep and also have a great rating with the BBB in Seattle. Just wrote them about the warranty. Their website is EZ to navigate , and they have new products to morph this unit into a combo or in a head cab.

After 40 years, I think this will take the place of all my big stuff. Feature-packed, compact, and "flexi"-ble. Just what I was looking for. The YouTube videos, reviews here at HC, and magazine reviews do not lie. Have Bogner, Fuchs, Mesa, Vox and more in my stable. This piece just moved up to the front of the line-up.

Don't know what year but serial is 0491.
Amp is crazy versatile. I play everything from Country, Church, Rock, Blues, Metal. Depending on your tube choice you can get anything out of it. A very cool feature on this amp is you can bias the amp right on the back. No jacking with taking the cover off or anything. It is even printed right on the back what the settings should be. Makes switching tubes a breze. All you need is a voltmeter.
Not quite 2 channel, but a footswitchable boost and master volume. You can control the amout of gain boosted, and the boost has a tone adjustment. Super effective. Has one effects loop which is very clean. I use this amp in church and in a rock/country cover band. The power is fantastic. 50/20 watt switch only adds to the tone choices.

I play a les paul, strat, and a early '90s yamaha pacifica. All sound amazing. I have never owned an amp this sensitive to dynamics. I have owned Peavey 5150 head, Mesa Reto-verb head, Mesa MarkIV, and Mesa f-30. This amp kills them all. When you know what you are doing with real tube amps like this one, you can dial up any sound with it. Each and every knob makes a huge difference in tone. You can hear the difference between all your pedals, and guitars. Finally I can hear all the mods in my Keeley pedals, and in my Fulltone pedals.

Seems like a tank. I would totally rely on this amp.

Have never had to use them, but have only heard great things about them.

Love this amp. Will NEVER get rid of, or sell. Have been playing for 15 years, and have never come across something this amazing. If lost I would shoot myself for being so incompetent. If stolen my 9mm will be looking for your tail. I compared it to all the boutique amps made. Picked this one because it is by far the most versatile.

purchased amp 4 mo. ago tube swaping is endless old lion kt66---beautiful bell basman sound eh kt 88 lots of headroom valve art el34s my personal favorite pre amp tubes make a bi diff too.. i tried mullards jan phillips chinese tung sol believe me they all make a diff it all depends on the use of application and you tweakin abilities

sound quality is where this amp shines its by far the best ive played ive owned a 63 bassman a black face twin 73 super lead 75 master volume sound city peavey heritage jcm 800 and more.. vintage marshalls have always been my favorite until the flexi 50 came along ..i have a custom shop strat a classic les paul js1000 and i just purchase a jackson rr5 each guitar takes on its own personality through this amp like none ive ever heard.. the key to the sound is in the tweakin of the amp..with the jackson i have to completely re eq the amp relative to the strat which the pick ups arent nearly as hot.. but when u find that sweat spot its amazing..

looks like a tank.. feels like a tank... i really dont know though ..like i said ive only owned this amp for 4 months hope it lasts like my marshalls

havent needed it yet ....

ive been playing for a long time..25+ seen aa lot of crazy stuff over the years heard a lot of good and not so good equiptment played many a club marshalls have been by far my best experience over the years old ones too... not the new ones although i havent payed the hand wired.. this thd is a keeper and is my presant amp i use to gig with ...wouldnt change a thang,,,

Amp was made in 2003. I primarily use the amp to play with friends and out occaisionally. Lots of tone shaping possibilities which could possibly be the reason some find it difficult to dial in a sound - extrememly sensitive to small changes. Love the fact that you can swap tubes - I can get chimey Fender to classic marshall no problem - metal requires a foot pedal to get close. To me the 20/50 watt setting has a lot more to with the quality of sound than the "amount" of sound. No reverb is bothersome.

I primarily is my JET Earlewood with this amp which has the ability to switch to humbucker of single coil. I have a ton of pedals, but mainly use analogman tube screamer, Anlgmn Boss DS-1, Angmn Chorus and HK reverb/echo. My band plays a huge spectrum of music - so, I find myself missing a channel switching amp at times. However, when I dial the sound in I am looking for this amp is as sweet or brutal as I want. I can see where others may have difficulty getting "a sound" from this amp - several times I questioned whether I liked this amp or not because I was spending time trying to recreate a particular sound. When I decided to find my sound is when I really began appreciating this amp.

My experience is this amp is built pretty solid. I move it around a lot and have never had any issues. Never needed to call THD.

No experience.

I've been playing off and on for 20 years - moreso in the past 5 years. If stolen, I might consider a channel switching amp, but in the end I would probably replace the THD. I might even consider a second THD and set it up differently. I receive many compliments on my sound and I happen to like it too.

Everybody knows the features, I'm not going to list them here. Lots of "candy" and things that seem great in theory, but ultimately are useless in practice!

Well, this is the MAJOR stumbling block for this amp. It just plain sounds awful on anything other than totally clean settings. Tried with a multitude of different tubes and a plethora of guitars, it always sounds like a piece of sh*t. A damned smelly piece, too! Just how the hell THD has created those wonderful soundclips in uses to promote this woeful amp is beyond my understanding. Must involve tons of outboard gear and studio trickery to create those tomes, because they just don't exists inside this sucker.

Seems reliable, but sounds like sh*t.

No idea, never bothered with them.

Compared to almost anything on the market, this amp sucks big time. It is incredibly bad sounding! And incredibly non-versatile. From all the frothy, rapturous write-ups it has had, I can't help but wonder if the reviewers were testing a different amp to the one that THD sell to the general public. Seriously deficient in every category, even the FX loop is a useless primitive piece of sh*t. Awful amp! Fortunately I was able to unload it on Ebay and get my money back. Shame, THD, shame!

Yowza, where to begin? This amp has a plethora of unusual options including footswitchable boost (with it's own gain and tone) and master volume (I find this particularly useless)as well as an input hi/low switch, and the ability to use almost any tube in existance to tweak your sound with. Another feature, in my eyes anyway, is the ability to carry a fifty watt amp around like it ain't no thing. It's about fifty pounds and appears to be about the size of a loaf of bread on steriods. Very useful in my opinion.

Let me start by saying I didn't love the overdriven sound it makes, although I did find a lot of good sounds in it. It just didn't give me a useable version of the Marshall sound I assumed it was going to create. The majority of everyone else posting here says otherwise, so I'll take their word for it, as they own it and I merely auditioned it, using a GE Smith Tele and a Gibson ES 339, as well as two Jetter pedals (red and blue) and my Landgraff Dynamic Overdrive. I also ran a Lee Jackson Mr. Springy reverb pedal, a Diaz Texas Tremadillo, and a Mad Professor Deep Blue Delay through the loop. The distortion pedals all sounded fantastic, better than any other amp I've tried them on. The pedals ran through the loop sounded reasonable, but I think they'd sound better run through the front, making the fx loop more of a feature to list on a brochure than a functional aspect of the amp. Regardless, I think that this little beast is great. I may end up buying it if I can find a better sounding reverb unit to run into it, but this is a small beef. It seems to be the perfect pedal player amp, and I can only imagine switching tubes will only further add to tonal variations.

No idea. The general consensus is that they're tough little bastards, and I'd be pretty comfortable gigging without a backup, maybe bring some spare tubes along just in case.

I called THD after my experience and asked them a few questions and they were more than happy to talk about their products with me.

I really liked it because it made my pedals sound pretty damned excellent. As a stand alone amp I think it'd be somewhat limited, but that's not much of a consideration for me as I'm basically looking for a small and awesome amp to run a bunch of pedals into. This would definitely fit the bill. A little spendy, yes, but an intriguing concept for an amp, and I'd be comfortable assuming that it'd be an investment that I'd have around for a long time.

The Flexi has a lot of features you expect (FX loop, eq), some less common (cut and tone knobs) and some features NO other amp has (tube swapping, easy re-biasing). I gig consistently with it in a rock/variety band. The master/boost foot switching capability makes the amp versatile enough to play in a band that handles a lot of different genres, but, being truly one channel, if you've got the amp tubed for a great dirty sound, it never gets really clean via a click of the "boost" switch and vice versa. I've found that it's close enough for my tastes, and the sweet tones you can dial in override this slight shortcoming.

My other beef is that, unlike the Univalve, the Flexi does not have an attenuator built in, presumably because of the complication of heat dissipation in a higher power amp. So, to get the full benefit of hearing different types of power tube saturation, you have to buy a Hotplate, or practice at full, ear-shattering volume.

The feature feature is the tube-swapping capability. Owning this amp is like a history lesson in tube amplification and provides countless hours of tinkering.

I run no effects and use both humbucker and single coil guitars. The whole point of the Flexi is that it has multiple personalities. And the different personalities the amp take on are based on the unique characteristics of different tube combinations rather than shallow modeling effects. Different tube types not only vary in distortion and tonality, but in sustain and response.

When I first got the Flexi, with it's stock tubes, it sounded kind of stunted to me, but the brilliance is in the capability to experiment. Right now, I am hooked on 6L6's for a present, more saturated sound. Last week, I ran El34's for what was nearly spot on old-school Van Halen "brown." KT88's are sweet for clean-ish jazz and Chicago blues. I use JJ Tesla tubes almost exclusively.

You can get anything from clean to SRV to ACDC to Malmsteen with some trial and error.

I have yet to have any concerns with any THD equipment. It turns out, you can even drop it.

This is easily my favorite amp. It takes time--you have to experiment for days, maybe weeks, with different tubes to find that sweet spot. But when you do, you do. I get guitarists at set break at every gig that compliment my tone and want to see my rig.

Also, this amp doesn't hide mistakes well. You have to be a good guitarist or willing to work your technique, or you'll hate it. But who wants to listen to a sloppy guitar player behind a wall of gain and effects anyway?

All of them are usfull

This is my favorite amp. Nothing I have played comes close. The harmonic are unreal

I never had a problem with it.

Ed and Andy and the rest of the THD family have always been good to me.

I have been playing 37 years at this time. Do I need to say more than this is the best amp I have ever played.

The Flexi 50???s features have been well stated by previous contributors. The Line- Out is fantastic. THD is one of the few manufacturers that have this area figured out. The tube swapping ability allows you to tailor the gain range and feel to suit your needs. I do not feel that this amp is a chameleon that can replicate the sound of the best vintage amplifiers. The Flexi has its own sound. The tube-swapping does affect the character, and how the amp reacts in a very audible and useful way. The Flexi is not a true channel-switcher, but you can set it up so that the Boost acts as your dirty channel. I wish that you could use the footswitch to toggle the lo/high input and the boost function independently. I still give it a 10 because the design is well thought out with many useful features that do not detract from the tone.

To start, let me say that I have found most of the reviews on this product to be exceedingly accurate. I have owned the Univalve, the Bivalve, and now I have settled on the Flexi. I play many styles of music including rock, blues, hip-hop, jazz, funk, r & b as well as some of the hard stuff. I play a Les Paul and a Tele and I use a Dr. Z Airbrake attenuator. Just as a base of reference, my favorite amplifiers aside from the THD line include: Marshall JCM 800 (good ones are very hard to find), Fender Super Reverb, Fender Vibro-King, Matchless DC-30, and Vox AC-30. The Flexi brings out the best in both guitars and brings out the differences in pickups and wood. It does clean tones, driven clean, and distortion equally well. The low end presence is excellent and you can achieve that percussive low end snap heard in Marshalls and Fenders. There is plenty of bass on tap, without any muddiness. Others have described the Flexi as a cross between a Marshall and a Fender with some AC-30 thrown in. I agree. The THD amps definitely have their own sound though.
The Flexi is extremely touch-sensitive and is a joy to play. In fact, the THD line has ruined most other amps for me. They feel sluggish in comparison. I can no longer stand to use overdrive/distortion boxes. I find that the Flexi, with its great sustain, allows me to connect notes easily and thus makes it a very forgiving amp to play in that respect. Sound characteristics are very difficult to describe, but I will do my best. The tone is 3-dimensional, meaning there is harmonic activity after a note is struck. Notes bloom. The bottom end is very tight. Even at high gain settings, you can hear each individual note in a chord. The Flexi is plenty bright, though not nearly as bright as a Marshall Plexi. It has a unique midrange that sits a bit lower in the frequency spectrum than that of a Marshall, and cuts well in a live situation.
I had the chance to a/b the Flexi with a Marshall Plexi Reissue. It is my opinion that the Flexi can do just about everything that the Marshall can do, and a million other things. I found the Plexi RI to be much looser and sloppier animal while the Flexi has a much tighter, more refined sound. The Marshall is way brighter which some players may prefer, especially those who are trying to accurately copy the Jimmy Page thing. It???s a very cool amp, but to my ears the Flexi blows it out of the water.

I have gigged extensively with both the Bivalve and the Flexi and I have never had an issue with either. One of the great benefits of the tube-swapping capability is that there is no need to see a tech. These things are built exceptionally well. I would feel confident buying one on the used market.

I have never had an issue with any of the THD products.

The THD Flexi represents one of the best values on the instrument market today. I have gone through over a dozen amplifiers in the last few years trying to find my sound: JCM-800, Marshall Slash Signature (Jubilee), Fender Super Reverb RI, Mesa Boogie DC-5, Fender Deville ???among many others. Being a career musician, I have had the opportunity to test out much of the high end gear out there as well: Bogner, Budda, Egnator, VHT, Dr. Z, Gibson, Top Hat, Victoria, Vox, Matchless??? So far, the Flexi is my hands down favorite.

see my prior review

Just wanted to update my prior review. I have now had this amp a couple of months, and the honeymoon is still not over! I am now running GTEL34M power tubes, v1 GT12AX7R, v2 GT12AX7M, v3 12AX7C preamp tubes into a 16ohm THD Hot Plate into a custom 4x12 cabinet loaded with Celestion 70/80's. My guitar is a Fender MIM Fat Strat with a Floyd Rose, loaded with a Seymour Duncan Custom Custom trembucker. I still have NO complaints with this amp, it sounds killer. The classic brit style crunch is incredible, I still feel like I got one helluva deal.

Still works perfect, very solid build.

I have spoken with Ed, about a Hot Plate issue, awesome guy, very helpful. THD really gets an 11 here!!

Absolutely no buyers remorse, I only wish I had bought this amp first and saved all the money I spent on other inferior heads. If you like classic Judas Priest, Iron Maiden or even early Van Halen with some tube experimentation this amp will nail that tone, But where it really excels is at giving you YOUR tone. One other thing that still irritates me is the guy who reviewed this amp in Guitar World put down as a CON "no high gain option". Duh! This was designed to produce classic rock tones in the style of the jcm-800 and plexi, not Nu-metal tones. That is like saying a Mesa Dual Rectumfrier has "no Vox AC15 option" Apples to Oranges dude!