I would be rather careful what you choose to connect to it as some of those amps were not particularly stable with all loads. They liked to blow up a lot. I would probably keep it between 4-8 ohms. No low or complex impedance i.e. no electrostats or ribbons. Resistive as opposed to capacitive.
Wow an Apt Holman Preamp. Make sure the Apt isn't outputting any DC. If I'm not mistaken, that was a AC (capacitor coupled) preamp.
Wow an Apt Holman Preamp. Make sure the Apt isn't outputting any DC. If I'm not mistaken, that was a AC (capacitor coupled) preamp.

