How does the TUBE MIX work and why does the amp get louder with the knob set to around 12:00?
The tube mix works by routing the audio signal to one pair of output tubes, the other pair of output tubes or a mix of the two pairs. All four power tubes are always on and “idling”. You adjust how much of your guitar signal gets routed to each pair of tubes with the TUBE MIX knob. The reason the volume increases slightly at the mid setting is simply because the signal is being routed to all four tubes and the combined output of four tubes is going to be greater than two. This is also the setting where maximum power output is realized.
