It's a HH IC100S head - as opposed to the IC100 i still have.
but what are the differences?
Well, the IC100 has two separate channels each with normal and bright inputs, spring reverb (same unit for both channels), and active treble and bass controls. Channel 1 has a tremolo effect controlled by speed and depth knobs on the front which i believe is also footswitchable, and a distortion circuit which is also footswitchable but has absolutely no controls for it other than on and off, although the EQ does change the character of the distortion significantly. It also has a half-power switch.
The IC100S is much more simple - still two channels with normal and bright inputs. But it has passive treble and bass controls on each channel, no reverb, and no tremolo. it does have the distortion - instead of the tremolo controls however, it has a gain control! woohoo! that was the only shortcoming of the IC100 imo. it still has the half-power switch and the footswitchable distortion.
Many people argue that the IC100S is the better of the two because the passive EQ makes the sound a bit less synthetic.
HH made great solid state amps back in their day - i wonder what the new HH amps are like? they market them as being "a reliable, usable transistor amp that is not trying to sound like a vintage valve amp". I've been saying we need more of those for so long, it'll be kinda weird if the company whose old amps i've been 'collecting' for a little while have come back and actually done just that.