For such an old Amp it is not worth doing a professional Repair.
I am Technician in Electronics and if i have had the right Information i will do the change of circuits by myself.
Last possibility is to exchange the whole PCB.
https://www.fullcompass.com/prod/218711-line-6-50-02-0186-main-pcb-for-spider-jam
If anyone can (want to) help me i will say thank You very much