78s need a different stylus (needle) and cartridge than 33-45 LPs (microgroove.) It's both the RPM and the shape of the record groove.

Jon: "...it hummed even when its off switch was off..."

Did it have a separate DC "wall wart" power supply? They're awful.

It's hard to do 45-78rpm right for under U$800 these days and that's just the turntable, no (pre)amp or speakers.