Hi, the 3CX1500D7 tube is a replacement for 2 3-500's, so a singlew one will be fine in your Henry amp, but a pair would not be a drop in replacement for several reasons. If you go with one of them as a replacement you will be fine, but 2 would not work as the power supply would require at least 2 amps to dully use the 2 tubes. One would be fine.