Power output with 1kHz test signal
- 8-ohm load at 1% THD: 0.76W
- 8-ohm load at 10% THD: 13.5W
- 4-ohm load at 1% THD: 0.33W
- 4-ohm load at 10% THD: 11.8W
The Hyperion HT-88 is a single-ended mono tube amplifier
utilizing two KT88 tubes triode connected in parallel. A pair of tube rectifiers gives one
plenty of tube glow to contemplate when playing music.
Chart 1 shows the frequency response of the amp with
varying loads. As can be seen, the output impedance, as judged by the closeness of spacing
between the curves of open-circuit, 8-ohm, and 4-ohm loading, is fairly high and typical
of many tube amplifiers. The variation with the NHT dummy speaker load is of the order of
+1.4/-1.8dB over the audio range.
Chart 2 illustrates how total harmonic distortion plus
noise vs. power varies for 1kHz and SMPTE IM test signals and 4- and 8-ohm loads. The
attainable maximum power, generally rated at 10% distortion for tube amps, is greatest
with an 8-ohm load on the 8-ohm output connection.
Total harmonic distortion plus noise as a function of
frequency at several different power levels is plotted in Chart 3. Laudable is the absence
of a rise in distortion at high frequencies. There is, however, the rise in distortion at
low frequencies, which is typical of most single-ended designs.
Damping factor vs. frequency as measured on the 8-ohm
output is shown in Chart 4 and is reasonably constant over the majority of the audio
A spectrum of the harmonic distortion and noise residue of
a 10W 1kHz test signal is plotted in Chart 5. The amount of AC-line harmonics is admirably
low. The signal-frequency harmonics are quite high and numerous, as the usual 10W level
that I do this test with is near this amplifier's power limits.