Conrad-Johnson Premier Eleven power amplifier:
Measurements part 3
Feeding a combined 19+20kHz signal into the Premier Eleven driving 8 ohms and doing another spectral analysis results in the data shown in fig.8. None of the artifacts in this figure is greater than 0.01%, and their level didn't increase into a 4 ohm load. This is superb performance for a tube amplifier. The THD+N vs level measurements in fig.9 show that the Premier Eleven gives its maximum output power and generally lowest distortion into a 4 ohm load. The actual clipping levels are shown in Table 1.

Fig.8 Conrad-Johnson Premier Eleven, HF intermodulation spectrum, DC-22kHz, 19+20kHz at 22.6W into 8 ohms (linear frequency scale).

Fig.9 Conrad-Johnson Premier Eleven, distortion (%) vs output power into (from bottom to top at 10W): 4 ohms, 8 ohms, and 2 ohms.

The Premier Eleven's test-bench results are good for a medium-power tube amplifier. The only matter of any concern is the slightly high low-frequency THD, but I wouldn't be put off by this if the amplifier auditioned positively—as it did!—Thomas J. Norton