I set up other scenarios with the bypass, providing a solid rhythm sound and adding more gain to the Rhythm channel and Lead channel, but being careful not to overdrive the input of the amp at the same time, as this changed the character of the sound of the guitar and added some unpleasant (to me) forms of distortion. The unit outputs 2 Volts at max before clipping, so there is overdrive potential there. Everything I tried without going over the top retained a sweet tube sound. I then thought of using the unit as a two-step overdrive, which might actually work well with some amps.

I switched to my ’71 Princeton Reverb and set up the basic sound at a volume where it was slightly overdriven. I then set up the unit with low gain and high volume on both channels to produce an intrinsically clean sound but with incremental increases in volume, and thus was able to overdrive the Princeton in steps, each step having a useful tone and volume in a blues gig setting—all the while producing the sweet sounds of a Princeton Reverb (with a 12" Weber Alnico) in torture… er, I mean “enhanced interrogation” mode.

Another cool thing about the unit is that its Volume control doesn’t start at the volume of the input guitar but can be used to lower the volume instead. In other words, if you really love the sound of your amp going straight out in bypass mode for solos, you can use the unit to instantly lower the volume and at the same time change the tone and character of the sound at two levels.

To round out the testing, I used a number of other amps, including a Fender ’69 Champ and ‘90s Hot Rod Deluxe, an Ampeg ’65 Reverberocket, an Allen “Old Flame” and a Clark Beaufort, as well as multiple guitars with both humbucking and single-coil pickups. In all cases, the amps and guitars sounded like their glorious selves, but with the addition of smooth, clean tube tone changes produced by the effect.

A few concerns surfaced during use. The unit became somewhat microphonic at high-gain settings, causing particularly the bypass switch to “clank” loudly when actuated. The unit ran quite warm, which is understandable since the tubes are run at normal (high) plate voltages. Just don’t block the vents. Of more concern is the wall wart power supply. It is a real oddball voltage and runs very warm. I personally would not gig with this pedal without a backup power supply. I checked the internet and found no aftermarket replacements. Digikey, the supplier cited in the instructions by Seymour Duncan, listed the part as obsolete and unavailable. I did not find its exclusion from the warranty, so along with all else, it’s covered for one year (except tubes, which are covered for 90 days). Tubes are tubes, and prone to failure. These particular tubes are heavy duty and designed for mechanical stimulation as might be found in handheld devices, such as microphones. I suspect they will last a long time if the unit is not abused.

There are no value markings on any of the controls, but the use of “chicken head” knobs makes clock-hour values calculable—I’ve used small color-coded stick on dots found at office supply stores to indicate approximate setup for particular amps and guitars with final tuning by ear.

The Final Mojo
This is by far the best blues-oriented pedal I have ever used. I have used many over many years, and I still own the original BK Butler Tube Driver, a TS-9,etc. The Twin Tube Blue is so good it doesn’t sound like a pedal. I need one.
Buy if...
you're a player of amplified blues with no hang-ups about pedals.
Skip if...
you're an acoustic player, or an amplified player who doesn't use effects.

MSRP $325 Seymour Duncan - seymourduncan.com