So, even though I have several different tuners, not counting the ones on my phone, I decided to plunk down about $30 for a pair of A440 tuning forks, each attached to a resonance box. I wanted to see if I could make the forks vibrate sympathetically when I played a perfect A. The forks come in pairs so you can hit one and hear the other vibrate sympathetically. They are available from most scientific supply stores, but you want to get them pitched for music, not the 256 Hz that many kits come with.

Haven’t been totally successful, but my A ear training is getting better.