I once read an interview to modern composer Max Richter where he discussed his setup and mentioned the HotTubes (possibly the original version from the 70s?) as a way of coloring digital sounds. At the time I was shopping around to put in place a small setup for doing electronic music, so I decided to give it a go, attracted by the low price. Since then, I used it to color a Moog Minitaur synth, assorted line levels signals from tape recorders and cd players, and also digitally synthesized sounds coming from my soundcard.
First impressions: the pedal is compact, so it won't take much space in your pedalboard, and it is very well built. It was obviously designed to resist muddy boots stepping on it, and that is probably the reason why the switch is a bit though. A minor nuisance if you are activating the effect using your hands (like I do) rather than your raging feet.
Controls: Volume, Overdrive and Tone. End of story. My approach is lot of simple effects, rather than huge overly complex pedals. The HotTubes is perfectly aligned with this philosophy. The Tone knob is activated by a dedicated switch, which I tend to activate more when I work with sounds on the higher side of the sound spectrum.
Sound: this is an overdrive, not a distortion pedal. If you're a guitar player, your setup is likely a Strato or a Tele jacked into a TwinReverb, if you know what I mean. You want to enrich your clean sound with harmonics, improve its presence, make it aggressive, but without trying to smash someone?s face. Combine the HotTubes with some ambient effects (I use it with a T2 reverb), and there will be magic.
Last note is about power consumption: I'll soon be moving to a power supply unit for my effects, but this pedal is still running on with its original battery after several hours of continuous usage. Oh, and the original battery is pretty cool, try googling for "Electro Harmonix batteries" :)