@chenry and many other
Many recommendations here for Sugden A21 get me interested mainly because of its value proposition. I am always craving for Class A sound. There are several version here: A21 (23 wpc to 8 ohms), A21ai (25 wpc to 8 ohms), A21SE Sig. (30 wpc to 8 ohms; 40 wpc to 4 ohms) and, in particular, their bass performance is sort of mixed bag and distinctive from each other according to the reviews:
(on A21ai) Even at their best, bass detail and drive were never among the A21ai’s strengths (Stereophile)
(on A21SE Sig.) Bass is powerful, controlled (TONE Audio Magazine); What I do wish for is more bass quality - quality, not quantity (6 moons Audio); With this amp, it was not speaker slam I heard but musical bass with air and space around (Audio Beatnik); Sugden miss a little in the bass compared to the Arcam (user feedback) and list goes on and on.
So, the bass performance on the regular A21 seems never being its strong suit and the bass on the more refined A21SE Sig. seems a mixed bag. I was not surprised by that because of the lower rated wattage into 8 ohms and NOT sustaining into 4 ohms (2 ohms is not reported) but wonder what is your listening experience?