[maxhifi]

Second harmonic distortion still cancels in the output stage... In the voltage amp there's not all that much distortion - RCA used that circuit over and over again and to be honest it sounds alright... it's a scaled up version of the circuit in most radios which have a push-pull output stage. The amplifier lacks global negative feedback, and the amplifier's overall distortion will be dominated by output stage distortion anyway, like a guitar amplifier. I have a pair of mi-12188a amps and have always liked them.

Keep in mind we're looking at 40s public address amplifiers here not a marantz 9 - this is from the era when records were 78RPM, tape recorders were from the future, and radio was mostly AM - speakers were full of all sorts of resonances and breakup modes and largely designed by trial and error in a pre-computer age. I have no idea how much THD and IMD a 1940s paper cone woofer with a paper surround makes below 100Hz, but I bet it's way more than the phase inverter in this amplifier! In the context of its application, these old amplifiers were over-qualified for the job, and it's amazing how well they hold up to this day in the context of much better speakers and program material.