The Vox Valvetronix range of amps was designed to use the advantages of both solid state and valve circuitry to make a warm authentic sounding amp that is easy to maintain and with plenty of features for the modern player including amp modeling to emulates the circuitry of other popular amplifiers.

The first Valvetronix Amps were the "Blue Series" introduced in July 2001. These are identifiable by their blue diamond grill cloth. These were the AD60 & AD120VT amps and the AD120VTH head. In 2003 the Blue VTX amps were introduced (AD60VTX and AD120VTX) with identical circuitry but different cabinet and with Celestion 'Neodog' speakers designed to give more punch and bass.

In 2004 Vox released the first Chrome Valvetronix amps - with chrome instead of cloth grills. Although these used the same 'valve reactor' technology as the Blue series they have fewer features but a much lower cost and were compliant with new import standards.The first chrome series models (AD15VT and AD30VT) were more of a practice amp that the prior Valvetronix amps. The competitive price and features of these chrome Valvetronix amps proved popular and Vox added the AD50VT, AD100VT (in 2005) and AD100VTH (in 2006)

In 2007 Vox introduced the Valvetronix XL (Extreme Lead) models. These were derived from the chrome series but with styling and tone designed to appeal to Metal players.

Source http://www.valvetronix.net.