How do i dummy load the 5150? (impulses)

I did a dummy load some years ago for about 20€.
Take a power resistor that match the resistance/impedence of your amp (for example if you select 8ohm impedence, buy a 8ohm resistor).
Solder a trs connector to 2 wires (+ and -) and the other side of the 2 wires to the resistor.
Connect the speaker out of your amp to the trs of the dummy load. That's all.
It's only a formality because when you use impulses you set the master volume (when there is one) to 0 and the resistor remains cold.
 
i still don't get this whole dummy load stuff
can`t i just leave the cabinet attached, and run a cable out of the loop into the interface?

Yes, you can, but the point of this thread is about trying to do this very thing, only have the cab NOT output any sound (or as close to no sound as possible).

Simply running the line out or FX send into the interface with a cab plugged in is not a problem at all, works fine. The issue specific to 5150/6505's is that the level of the FX send is dependent on where the post gain is set...Which can be a bit loud for most people.

My solution was pretty easy. I used my ABY pedal and an old EQ pedal I had laying around. I went out of the head via FX send into an ABY pedal...one side went to my interface and the other side went into my EQ pedal. I put all the sliders all the way down, including the level slider (so around 40 dB of gain/volume reduction) and then the output of the EQ pedal went into the FX return of my amp. I had my post gain set around 2.5, which is plenty loud enough and the output of my cab was below bedroom level. Basically the EQ acted as a master volume.

I'd think you could do the same thing with a DI box? Run the "through" into an EQ pedal and then back into the amp, and the DI out to the interface?
 
Uh... he said "and then the output of the EQ pedal went into the FX return of my amp."