After carefully installing the Triode Lab 2A3 EVO’s tubes, I performed a complete set of tests of the amplifier with my Audio Precision SYS2722 system1 using the Electro-Harmonix 2A3 Gold output tubes, then repeated the testing with the KR 2A3 tubes that KM told me he preferred. As usual, I waited for an hour after powering up the amplifier before starting the testing.
The 2A3 EVO inverted polarity from both the 4 ohm and 8 ohm output transformer taps. The input impedance was a usefully high 61k ohms at 20Hz and 1kHz, 41k ohms at 20kHz. The source impedance from the 8 ohm output transformer taps with the KR tubes was relatively low, at 1
