Dont know enough about your experiences.
I would suggest a cheap DDS pcb/box from ebay, so you can create some signals to drive your experiments. Alternatively a used old school freq gen, but i think the dds are better value.
Then you can start playing with bread boarding some simple circuits. Something with transistors like audio amps, 555 timers, 317 low voltage psu (get a 24v ac plug pack).
Later on you can get a cheap korad style psu or something when you save some money.
I think its time to start building a parts collection, either from grab bags, kits, or salvaging broken equipment. Not sure I would recommend you play with mains equipment.