My friend has a Harmon Kardon A500 tube amp from the 1960's that has 4,8,and 16 ohm taps. It has gobs of headroom and drives his 4 ohm ADS L710 speakers with ease. It was recently overhauled and is still breaking in. He also has a mint Fisher 400 tube receiver that also has 4,8,and 16 ohm taps. He just bought a Dynaco ST-70 so I believe he might be willing to sell the HK or the Fisher. I can ask if you're interested.