The wattage rating of an amplifier is a very , very loose measurement of how loud the entire system will be perceived . The actual number will depend on the amp design , the cab , and the loudspeaker driver used . So there ' s no real correct answer . The simple fact you ' re asking how many transistor amp watts would equal tube amp watts should tell you that using the amplifier wattage rating is not helpful . Now the reason the tube amp is perceived louder has to do with distortion . If you use an overdrive channel or pedal with prominent even order distortion for example , modelling amps or a tube screamer based pedal then your wattage measurement is going to be a bit closer to the tube amp measurement .