Pros: Excellent sound for the age.
Cons: Not enough volume with smartphones
I bought these new in 1978 for 1 or $200, can't remember. They were the best sounding for my budget at the time. Smooth and flat sounding. Needs lots of horse power to get loud. They still sound good for 30+ yr. old headphones. I bought an HTC DNA smartphone that has "Beats Audio" a built in 2.55v amp for phone speaker and headsets. The HP-3s are 'just sufficient' at full volume but no distortion at least. You'll need a 3.5mm adapter for the 1/8" plug which is a pain lugging it around. I think it's time to update (for the phone at least!).