The Bottlehead amps have zero NFB. The amps are safe with no speakers attached. I often switch both the left and right speaker leads to get correct absolute phase (I use dual banana plugs for this reason). There is no speaker load there for several seconds when I fumble about. Longer makes no difference.
An amp like the Dynaco ST-70 could go into oscillation. (I've got one of those too.)
I hope this answers your question.
Yes it helps, thanks for the sanity check Grainger. I thought that was the case, but wanted another opinion!!
