Futterman OTL- best I’ve owned or heard
Heathkit UA2s, Eico HF14 or other 6BQ5 amp with good iron
EL34, 6L6 or 7591 tube amp (see above) like ST70, Eico HF87, MC225 or Klimt Kent and 8B if you’re well heeled
Scott 222s, Fisher X100s and other vintage integrateds can be wonderful, too
I prefer tubes, clearly, and feedback is necessary in my experience— I’ve had several pairs over the past 30 years-:)