Are MOSFET's voltage, not current, devices?

Transistors and tubes do not create voltage or current. They let current pass through them. The voltage that moves the current comes from the power supply. The current output is determined by the power supply voltage and resistor values around the transistors.

Transistors/tubes act like water valves - the valves neither create the water nor the water pressure behind them. They simply let water pass that's already there - just like transistors which pass current that's already there (simply put).

Gs,

I think you may be a bit confused, you described a diode.

From a quick google:

"Acronym for metal-oxide semiconductor field-effect transistor, a common type of transistor in which charge carriers, such as electrons, flow along channels. The width of the channel, which determines how well the device conducts, is controlled by an electrode called the gate, separated from channel by a thin layer of oxide insulation. The insulation keeps current from flowing between the gate and channel.

MOSFETs are useful for high-speed switching applications and also on integrated circuits in computers."

MOSFETS do switch faster than traditional NPN or PNP transistors, however they also produce measurable (and more importantly audible) noise. So there's a tradeoff between transisents and noise, both approaches have known design techniques to deal with the shortcomings. For what it's worth most solid state amplifiers that I prefer are discreet amps, MOSFETS seem a bit edgy to my ears.

Reagrds, Jeff ('phile and semiconductor dude for the last 20+ years)

In a nutshell, transistors of all types are current devices, whereas tubes are voltage devices. In most of the "better" solid-state amps, the input stage uses FET's, the gain stage has MOSFET's, and the output stage has bi-polar transistors. This arrangement is usually chosen because it capitalizes on the best characteristics of each type of transistor.