That 18-watt Lamm amp really gives you more options than most single-ended triode amps do. I think you can reasonably look at speakers below 95 dB efficiency, assuming a benign impedance curve. I've shown benign 92-dB speakers with SET amps of 5, 6, 12 and 25 watts, and the only time we ran into audible clipping was with very loud solo piano on the 5-watt amp, and real-world that conservatively rated Lamm amp is probably more powerful than the 25-watter.
Duke
dealer/manufacturer
Duke
dealer/manufacturer