FWIW, a few years ago I was breaking rear spokes on the freewheel side, and the guys on here told me to check my spoke tension more carefully when I built the wheel (I had not been checking it properly). Although I was too cheap to buy a tensiometer, I found that by squeezing each pair of spokes together where they cross, any incorrectly-tensioned spokes become glaringly obvious. I've been doing that ever since, and haven't had any broken spokes for a long time.