I'm seeing a 50 dollar MSRP difference so that's not that much less. Still, that's a good question but my guess is maybe because the G20 has a more complex EQ section? Maybe also because it's supposedly true class A. It probably also cost a little more to build the "tolex" covered cabinet for the G20 versus the metal cage for the T50. But I don't think it's a quality difference. They are all pretty cheap amps. Thin boards and generic components. I have a Tri Rec and a V22 HD. The Tri Rec I bought used but it's their most expensive amp. It doesn't seem any better built in terms of overall build. Besides the higher power requiring bigger, more expensive transformers and more tubes, it's got far more internal components and is a more complex with multiple boards, relays and their Varipower. The boards and the components themselves don't look to be of any better quality. I assume this would probably hold true across their entire line but you never know.