I just played with a steel player who had one of these, and it sounds like it might be a pretty baddass tube pre for bass as well. Anyone tried it? http://www.sarnomusicsolutions.com/products/sgbb.html
Yeah, it seems like it could be like one of the tiny tube pre's (presonus, ART), but made with better quality parts and handmade. Next time I'm free enough to borrow it, I'm going to see if it can tube up something. I always liked the tiny tube pre's, and I've tried a few of the cheap ones, but they always added so much noise and sometimes even picked up radio stations -- total deal breakers. Maybe this thing will sound cool and at $300, it's not ridiculously priced.
Commercial Disclaimer: I'm the manufacturer of this product responding to comments on this thread. The SGBB has a true 300+ volt power supply and also a DC heater supply. It's very quiet and robust, hand made by my wife and myself in St. Louis, MO. It's the real deal, boutique, professional quality kind of device. I wouldn't call it a preamp though. It's a buffer with no tone shaping or voicing. Flat response on out to 200kHz. Variable input impedance to tailor the treble peak amplitude of passive magnetic pickups. The tube factor allows your bass or whatever instrument to have the reactivity and tonal response of plugging directly into a tube input, but since it has a low-z output buffer, it can drive lots of pedals and cables without loss or unwanted coloration. Very useful as the first device on a pedalboard, and especially useful with an all transistor rig. Best, Brad Sarno www.sarnomusicsolutions.com