Help me understand Mark V's output knob

[marion]

I am new to using Mark V:90. I had several Mark IIIs in the past though (now down to 1) so I understand Marks but first time to using the output knob. Does the output knob work the same as putting a volume pedal in the effect loop? I don't think so. Let me explain. Here are my settings:

Mark V Channel 1: Fat 45W, gain maxed, master maxed, output 9 o'clock.
Mark III Rhy1 15W (simulclass): vol knob maxed, treble 7, master maxed, volume pedal adjusted to same level as the Mark V

Result: Mark V sounds like the power tube is pushed and distorting which I like very much while the Mark III is still clean. BTW, I tried using low and high impedance volume pedals on the Mark III and results are the same.

So, I'm curious where is the output knob placed in the Mark V circuit? Is it after the power tubes and acts like an attenuator?

 

[Don]

The Output control on the Mark V is after V6B (effects return stage) and before V7 (phase inverter).

I've noticed that running a volume pedal in the loop of the Mark V:25 and setting the channel master high adds a lot of distortion. It's not power tube or phase inverter distortion. I think it might be the GEQ being overdriven.

 

[marion]

Very interesting. I thought I'm finally hearing power tube distortion as I haven't heard one in person.