Imagine the tiny signal coming out of a moving coil phono cartridge: 30,000 to 50,000 times smaller than what comes out of your preamplifier. It has come a long way and through much amplification to become this much bigger. Like a weary long distance traveler who struggles to stay intact along the way, the journey was a difficult one with detours, traps, pitfalls and dangers aplenty. Bruised and somewhat battered, the signal is ready to meet its next challenge, getting through the gates of hell where it will be suddenly transformed from a pristine voltage to a powerful one-eyed cyclops with a high-wattage club, ready to do battle with the loudspeaker.
The point of entry for our beleaguered signal is a critical juncture where solid state amplifiers fail to meet the challenge without loss. And once musical details are lost they can never be regained. Whatever shape our signal at the output of the preamp, it is critical we lose nothing more, and that is the first task of every power amplifier. Unfortunately most fail. Can it ever work? Yes, but not with the current-centric attributes of solid state. For this task we need a pure voltage amplifying device with many electrons, and there is only one of those. It is called a vacuum tube.
Now, many of you no doubt think "oh, this is just Paul trying to sell an amplifier" and you would be right. But! Here's where logic does not properly extend. If my only goal were to sell you an amplifier it sure as heck would not be by adding a vacuum tube to its input. No, it would be far easier to place what we have always done; a transistor. But it would not be right and I would forever be listening to significantly compromised sound, which I am not. And this admission is from a person who has sworn an oath to never make products with tubes inside; an oath I have successfully clung to for 40 years.
They say with age comes wisdom, but in my case abandoning my oath came not from wisdom but letting my prejudice go so I could observe the truth, even if it violated my belief system. Trial after trial between all manner of solid state devices convinced me of the tube's amazing abilities, so superior to that of a FET or bipolar there was no contest. None at all.
But tubes are not good at much else in a power amplifier and we will examine that next.
