Integrated Amplifiers

I discuss the practical realities of ultralinear (UL) and triode operation in our boxout but the headline figures for EAT's first, and very substantial tube amplifier, are all very positive. EAT rates the E-Glo i at 2x35W into 8/4ohm loads (via the 8 and 4ohm taps) in UL mode and 2x18W into 8/4ohm in triode mode – conservative figures for a pair of KT88s but precisely met on the lab bench. Under dynamic conditions, and relaxing the distortion limit slightly from 1% to 2%, the E-Glo i marginally extends its reach to deliver 39W/8ohm and 41W/4ohm (via 8 and 4ohm taps, respectively) while still offering 41W/2ohm and 33W/1ohm via the 4ohm tap [see Graph 1, below]. Power output almost exactly halves in triode mode while overall gain is +30dB (+31dB in UL) and the A-wtd S/N is a very respectable 93.5dB (re. 0dBW) – so this is a very quiet tube amplifier, well suited to above-average sensitivity loudspeakers.

In common with almost all tube amps, THD is lowest through critical midband frequencies – a mere 0.012%/1kHz in UL mode at 1W/8ohm – before increasing at low frequency/higher power through transformer core saturation and high frequency/higher power as the influence of NF is reduced [see Graph 2, below]. For example, at 1W/8ohm THD is 0.2%/20Hz, increasing to 1.2%/20Hz at 10W. The damping factor at low bass frequencies is also boosted over some other tube amps thanks to its ~1ohm source impedance. This also reduces the variance in system response with speakers exhibiting swings in load. Into a 'flat' 8ohm load the response reaches down to +0.1dB/10Hz with a +1dB/1Hz 'bump', and up to ±0.04dB/20kHz and –0.9dB/100kHz. Triode mode is v. slightly (but inaudibly) different at –2.2dB/100kHz. PM