Highly recommend is the David Berning ZH-270 OTL. It has no problems with lower impedences because of its ability to match speaker impedence and increase power output into these more difficult loads. This design is most likely the most stable OTL design and does not use "brute force" technology by any means, uses a patended resulting in a more stable amplifier. Its power consumption at idle is a mere 100W and a maximum of 300W at full power output, you can adjust feedback on the fly, is stable into 2 ohms (and probably lower), tube life is an estimated 20 years, and can be mated with any speaker that a solid state amplifer within the similar equivilant output power can be mated to. Only most of the solid states don't sound as good as an OTL :)
Chris
Chris