Preamp tubes in a dedicated power amp??

[emperor_black]

Why are there preamp tubes in a stand-alone power amp like the Carvin TS100? ..and in the Mesa 20/20.

I thought a pre-amp is the actual sound of an amp which the power amp just amplifies. if there's a preamp ckt. does that mean that some coloring will take place? Then different power amps with the same preamp should have different sounds!

[marcus]

Power amps do color your sound a little bit, but the effect is more subtle than what you usually get in your pre-amp. Pre-amp tubes are way overdriven to produce distortion, while power amp tubes don't usually distort until they are driven to really loud volumes.

In general, the pre-amp tubes that are used in a power amp are not used to generate distortion. I am not an expert, but these kinds of tubes can also be used for such things as the phase-inverter, input stage, and probably other such circuits.

[emperor_black]

that's what I assumed. Those preamp tubes are there to act as a "bridge" to carry over the input signal to the power amps.

[thebisch]

Here is the problem. A "preamp" tube is only a preamp tube if it is used in a preamp circuit. In a power amp 12ax7s are used as input drivers and phase inverters. HiFi tube amps are where you usually find input drivers. I don't know if guitar power amps typically have an input driver.