I performed the measurements of the LSA VT-70 with my Audio Precision SYS2722 system.1 Although potentiometers on the top panel allow the bias currents for the output tubes to be adjusted, I understand that these currents are set by the manufacturer before the amplifier leaves the factory. Nevertheless, before I started the testing, I checked the tube bias with the front-panel meters after a 30-minute warm-up; with no signal and the volume control set to its minimum, the bias was very close to an indicated “100” for each tube.
The LSA VT-70 preserved absolute polarity, ie, was noninverting, from both of its output transformer taps, from the headphone output, and from the preamplifier output. The maximum voltage gain at 1kHz from the loudspeaker outputs into
