Hi folks!

Just bought myself a Blackstar HT-5 amphead. It's a 5W tube head.
Outputs on the back are 1x 16 ohm and 1x 8 ohm.
Im all new to tubestuff, only owned a line6 spider 2 combo before and after only a podxt live board. I read that i MUST have a cab connected in order to use the head so the outputs have load on them. Load dummys are expensive.
Can't afford a cab atm but wanna try the head out using the headphones output.
What i do have tho is a "GAS" 10" speaker saying 180W 8ohm on it. I figured that i could just sodler a 1/4 plug on it and use it as load but still use headphoes out? (hopefully the head turn speaker out off when plugging something in phones out)

Would this work or will i burn the head?

Well, I run my head with the speaker from my combo so that will be fine. My head doesn't have a headphone put though so i'm not sure about that part, but it should be ok.
I should add that the GAS speaker is normally just a cheap brand for use in cars/home.
Think it's a bass element. Remember using them in my homebuildt speakers like 10 years ago. But as i said, im only gonna use it as a load, not to play through it.