Had the pleasure of servicing a Hellcat combo this week. A low serial number from around 2003 or 2004 built to the usual high Cornford standard. Compared with your average production amp like Fender and Marshall it’s the little things that I notice on these amps that make them stand out. For example aerospace PTFE wiring, anti surge mains lead, high audio quality coupling caps, nyloc secured valve bases. All of these factors are likely to ensure that Cornford amps, though not manufactured anymore will be around for decades to come.
Channel switching problems can be cured by replacing the appropriate opto coupler. Original part is no longer easy to obtain but try subbing with VTL5C3 or 5C1.