Is it detrimental to the head at all to run it without a cab and instead use the headphone out? I've heard various conflicting stories about this and was holing someone could clarify. It's a WA300 solid state if that helps.
Powering up an amplifier with no load is only dangerous for valve heads to my knowledge. You should be fine.
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Ziphoblat answered your question, I just wanted to ask what you think of the WA300 head? Haven't seen many reviews go up about them yet!
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Cheers Ziphoblat, that helps a lot.

@Nutter, it's a pretty solid head for the price, although I haven't really had a chance to run it in a band setting yet.