input loopthrough works, as it was a t93 amplifier:

both input connectors are short-circuit under the point of view of the dc current.

therefore whenever you inject vdc in one of them, there will be the same voltage in the other connector:

• with the switch set to off there is no vdc through the coaxial cable.
• with the switch set to on, the amplifier sends 24 vdc to the input and they are available in both connectors.

if you loopthrough more than two amplifiers: