There are 3 types of amps around:
1. Tube amp
2. Hybrid amp
3. Solid state amp
The Marshall AVT are Hybrid amps.
It has a TUBE in it's Pre-amp section, and a solid state in the Post-amp section.
TUBE amps, as most people know em... are full tube (both pre-amp and power-amp stage)
Each type of amp has it's own pros and cons, here are some common words used to describe em:
1. Tube Amp -- Most people claim it's the best sounding because there is compression, rather than clipping when the amp distorts (thus more natural sounding to our ears) Also, tube amps distort asymetrically (giving the effect of a "warm" tube distortion)
2. Solid State amp -- Cheapest to manufacture amongst all 3 types. "Tougher" (as it is physically less sensitive compared to Tube amps, able to take tougher bumps etc) Sharp sounding, "sterile" clean, sharp sounding distortions.
3. Hybrid Amp -- Tries to merge the best of both worlds. Cheaper than a full tube amp. Tries to be tubish sounding, solid state means less money spent on tube replacements.
Just my little 2cents worth, please don't shoot me down for my inaccurate choice of words
Hope it helps VaiSteve, you can do a google search if you'd like to read up more on how these amps compare.