First system in 1973 - I was 16 years old and drove from PA to East Orange NJ to some "wholesale" audio warehouse. I found it through an ad in Stereo Review. I had a pocket full of cash and this place was in a pretty bad section of town. I parked on the street and ran to the front door (the door was "armored", and all the windows had bars). Nothing was on display; you just told the guy behind the counter what you wanted, and he went into a back room and brought out the boxes. I bought a Sansui 881 receiver and a Technics turntable.
For speakers, my brother and I went to the electronics store in our hometown. It was set up like an auto parts store, with a couple of clerks standing behind a counter, and all the parts on shelves behind them. One of the clerks helped us pick out woofers, tweeters, midrange drivers, and crossovers for a three-way speaker. We then stopped at the lumber yard and picked up the wood to build the boxes, which we stuffed with extra insulation from the attic. The speakers probably sucked, but boy were they loud!