So I didn't know this was possible, but...

[WickedCoach]

So this is my amp set up. I have a 5 watt blackheart head with a 1x12 cab, and a 15 watt blackheart combo amp. I was playing around with different sounds, seeing which was better and I was running the combo using the 1x12 as an extension cab. I then plugged in and played the 5 watt head and realized that the combo was now running as an extension cab to the head. Just to be sure, I turned the combo off and unplugged it and it was still running as a cab. So 1- I never realized this was possible, and 2- is this perfectly safe for both amps to run like this?

 

[Little Pigbacon]

Re: So I didn't know this was possible, but...

A quick look at the manual seems to imply the combo was not meant to run this way. If you're running the head into the combo's built-in speaker, and you haven't disconnected that speaker from the combo's own amplifier in order to do it, then you're running two amplifiers in parallel at their outputs. Bad.

If you want to run the head into the combo's speaker, turn the combo off and disconnect the speaker. Then connect the head to the speaker and turn the head on.

http://www.blackhearteng.com/pdf/BH15-112_OM.pdf