foxwelljsly
Me too, I ate one sour too.
The Harman/Kardon HK6150 is a really decent budget amplifier. Assuming 30wpc is enough to drive your Celef 'speakers to the levels that you tend to listen at, then I'd look to general system optimization (proper stands, 'speaker placement, etc.) before changing anything out.
Also, how do you know what state your LPs are in until you've given them a go? I've many here that were pressed in the 1950s, most of which started out being played on Gerrard, Dual, and even BSR(!) record changers back before many on here were born. Bar none, these are among the best sounding records I've ever heard. H/K integrated amps of this period had quite decent discrete MM phono stages with 47kOhm//125pF input loading, which ends up working very well with a wide range of cartridges. Why not dust off that old Dual, treat it to a new belt, and see what you've got?
I used a Harman Kardon PM645Vxi for a year or so before buying an Inca Tech Claymore II. Good amp. I also used a very late black 8000A for a few years. They are perfectly good and a steal at current S/H prices, but the RCA sockets on the back are flimsier than a flimsy thing. If it sounds like shit, then it probably needs a recap and a clean.
Still, for £300, you can't beat a 90's Exposure integrated, but that will probably also need a service too.