I'm having trouble understanding how the Ampeg R-12-R preamp works. It's a push-pull 6V6-based design with a paraphase phase inverter and all-octal tubeset, incorporating on-board tremolo and reverb. I'm pretty sure I get how the tremolo works: a triple RC network between anode and grid of the 2nd triode V1b, and output fed into the circuit between the PI and grids of the power tubes. But the reverb mystifies me. I've traced the signal path from input on the attached image (whole schematic included as an attachment) from input jack through V1a, then through V2a and V3a to the reverb tank (so far in green). After the tank (highlighted yellow) the signal path (now pink) goes through V3b and the "dimension" pot, then back to V2b, and thence to the PI. What I don't understand is that the reverb tank seems to sit squarely in the signal path, without any circuit "fork" where dry and wet signal intersect. If the reverb is turned off, then how does signal bypass it and make its way "dry" to the PI? Maybe there's just something about how a reverb circuit (or tank) works that I don't understand. I'm not even sure whether the reverb is "on" when the switch is open, or when it's closed. Any help will be greatly appreciated.