Hi @atmasphere ,
It is true.
When I bought vintage Altec 604 "e" from mid 60x, coaxial with horn tweeter and ~98dB sensitivity.
I used it with McIntosh MC30 amp from end of 50x.
Some vintage lovers thing it is a great idea to use components designed and made in similar time. But they are wrong!
I used MC30 with Spendor 2/3 speakers (88dB sensitivity). They sounded great together.
Altec 604e worked OK with MC30, but I discovered a real Altec's capability only when I started use them with 300B SET amp. McIntosh with 5 tubes stages, a number of local
feedbacks, a global feedback and dumping factor 12 - was great with mid-sensitive speakers but sounded rough and sloppy with high sensitivity horn speakers. In contrast SET with zero feedback and dumping factor 5 sounded smooth and transparent with Altec 604e.
I think the other drawback of global feedback - it is reduce sense of real life dynamic and micro dynamic. But, despite this, I steel use phono stage with feedback RIAA correction based of EAR 834p schematics.
Regards,
Alex