"Reussenzehn" is a little manufacturer of Valve-Amps. The founder Thomas Reussenzehn is well known for his handmade amps, but also for his eccentric way with customers.
Three different versions exist:
Studio Bass Amplifier
That is the one as seen on my review. It is a simple but good sounding 15 watt all-valve amp. It is the "basic-amp"
Bass Studio Amp De Luxe
That amp is based on the Studio Bass Amplifier, but with two mixable inputs. Both inputs have a switchable "Contour-Preset"
Studio Amp & Tube DI
25 Watt single ended ClassA Amp. It works with a KT120 with two switchable anode voltages. So you can get two different sounds. You can also switch to a EL34, 6550, 6L6 or KT88 without any bias-correction.
All three amps can used without a speaker-load.