Running a head without a speaker load

[Robscott]

I just got a Markbass Little Mark Tube 500. Markbass say all their amps can be run without a speaker load. I'm a bit surprised by that, cos although it's a Class D amp it has a tube preamp. I don't doubt Markbass's advice but I'm curious to know why some heads need a load and others don't. Anyone know?

 

[Rick James]

A direct coupled SS amp with no load doesn't have any current passed by the output devices, so there's no problem. A tube amp's output devices, the power tubes, always pass current into the output transformer primary winding. If there's no load on the output transformer secondary winding, or if the load impedance is too high, damage can occur. A tube pre-amp always has a load, the next amp stage, so it's not affected by the presence or lack of a speaker.

 

[Old Garage-Bander]

The tube in the preamp has nothing to do with driving the speaker output.
It is there only to provide tone shaping in the preamp.
The concern about loading only applies to the amp's output stage.

I just got a Markbass Little Mark Tube 500. Markbass say all their amps can be run without a speaker load. I'm a bit surprised by that, cos although it's a Class D amp it has a tube preamp. I don't doubt Markbass's advice but I'm curious to know why some heads need a load and others don't. Anyone know?