Quote Originally Posted by dave.king1 View Post
I'm hearing you but my tiny mind is still struggling to understand why the signal chain was apparently complete regardless of switch position with the valve removed.
Because it wasn't.

With the valve removed and the switch in the valve position, there was no sound. With the valve removed and the switch in the valve bypass position there was sound. So the switch worked, the two paths worked (provided the valve was installed) but no sonic difference meant the valve was operating cleanly at the volumes Fender3x was using.

Jim, the circuit is in parallel but there are transistor switches being used to switch the signal path. SO one transistor is turned on and the other turned off (and vice versa) to bring the valve circuit in and turn off the bypass path, or else to open up the bypass path and cut off the valve path.