I downloaded the schematic. Thanks, Simon, for also taking a look. I came to the same conclusion, but my read on such things is not to be trusted. so nice to have somebody who knows what they're doing take a look too.
It also looks to me like the tube circuit comes in after everything else, just before the power amp. No need to pull it out to find out what it sounds like without the tube. It has a switch that will do that. To my ear it sounds exactly the same with the tube in or the tube out. But it may be, as Simon suggests, because I am playing at garage volumes with the master barely cracked open.