What is tube:
Tube technology, ancient by todays digital standards, is the art of using vaccum tubes filled with a nobel gas as a way of manipulating electrons. Tubes, also called valves across the pond, amplify the original signal feed to them by passing the signal though a voltage plate. The voltage plate(s) in tubes get their power from a big ass transformer that steps your household voltage of 120vac to around 400vac for a 25w amp that is rectified e.g. converted to DC voltage and filterd through large capacitors.
Solid state technology is the use of solid mattter semi-conductors(silicon) in various devices to manipulate the flow of electrons, made available to us by the alien vessel that crashed in roswell in 1947, and uses a device called a trasister to replace tubes. Transisters can perform the same function as tubes, more effeciently than tubes, using less power and and lossing less energy to heat. And because transisters are so effecient, there in is the difference in the tone of both type of amps.
Tubes are clumbsy, in-effecient, and have a built in defect. By cranking your tube amp up to ten, you are rising the plate voltage to a piont where the original signal(your guitar) is overdriven and becomes distorted. however this defect in the design is what make them sound so good. The tubes can then become oversatuated with electrons and will start to cause the output signal to create overtones and feed back. Because of the style music of the time, most manufactures tried to prevent distortion from happening by making power transformers and tubes larger. That is why the Twin and Concert amps are so loud. It was meant to keep the sound clean, without distorting at high volumes.
Solidstate amps were designed to elimnate distortion at high volumes. And by players' standards they did it too well. Solidstate guitar amps today, for the most part are designed to emulate the defect of tube technology because it is a prefered sound. So you may be asking why even make solidstate amps at all....its cheaper technology to manufacture.
As for the Crate amp...keep in mind, every amp I own is a vintage tube amp from the 50's, so Im a little partial......is a hybrid amp( I think) and combines both solidstate transistors and tubes. For my taste, newer tube amps, hybrid or traditional, do not sound like the original ones, even the re=issue stuff isn't the same to my ears. More crisp and industrial sounding instead of warm and mushy. Its very hard to descibe in detail the differences in tone between the two technoloies, you just have to be around the things and get to know them.......but for the price of the brand new Crate, you may be able to find a deccent vintage tube amp.....Gibson and silvertone vintage amps are a great bargan right now because too many people mistakenly think if does'nt say fender on the grill then its no good. Bullshit. I would go that route, but like foo said use what you think sounds good