Tubed preamplifiers have a well-earned reputation as system busters. Many of them during warmup produce horrendous bangs or plops so severe that every speaker fuse in the system blows. If fuses are absent, or rated too high to protect things, the amplifier, speakers, or both are likely to blow up (not literally; they just twitch once and lie down dead). The PV-5 contains one of the most effective pop suppressors I've encountered, and produces no noise whatsoever during warmups and turnoffs.
Altec A-7
A highly efficient horn-loaded system for use in large to very large listening rooms (at least 15' from the listening area), or for very high-volume "Row-A" listening. Excellent woofer-tweeter blending, moderately deep (useful 45Hz limit in most rooms) and very taut, well-defined low end. Highs smooth and slightly soft, yielding most natural high-end quality at high listening levels. Middles smooth, rather forward, placing closely miked instruments somewhat in front of the system itself.