Regarding this statement; "...It was also, by all accounts, an amplifier-killer, its impedance featuring a punishing combination of low magnitude and high phase angle!..."
During a period in the early 1970's I ran a service center for a major audio distributor in northern Ohio called Bullet Distributing (Tokyo Shapiro). I never saw an amplifier get killed by an AR 3a. I owned a pair of 3a's myself and my amps never had any difficulty driving them.
However what was an amp killer was the EPI (Epicure) line. These speakers dropped down to around 2.5 ~ 3 ohms at certain low frequencies and we were at times unindated with blown amps from these. I remember the Sherwood Darlington oputput amps were particularly popular but they kept tripping the protect relay when used with the EPI's. Their answer to this was to change the tripping point which resulted in a massive number of smoked output stages.
Salesmen in our company gave me grief because they wanted to sell these two in combination and I was telling my customers why their Sherwood amps were blowing up. I got called to the carpet for telling the truth.
