All things being equal (same power tubes, OT, speakers, etc.), would 2 amps sound the same in terms of volume if they had a different preamp? Specifically, for simple amps which only have 1 preamp tube and a PI before the power tubes, would I get more volume by putting 2 preamp tubes before the PI? I would think that once the amp is up into the top end of its volume range, the signal is very compressed, so adding another preamp tube is just going to raise the signal going into the power tubes, ultimately compressing them quicker, right? So in essence, you end up with more compression but not necessarily more volume. Ultimately, what raised this question is that I have 2 18 watt amplifiers that sound very different in terms of loudness (marshall 18 watt and DR Z MAZ 18). I switched the speakers and realized that the speakers were a bit source of the volume difference. But I also noticed that the MAZ has 2 preamp tubes before the PI. Hence, it just got me thinking. And exactly what is "18 watts" a measure of? plate dissipation? Probably not. Hoping an amp expert can explain.