WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
Building, troubleshooting and testing of these amplifiers should only be
performed by someone who is thoroughly familiar with
the safety precautions around high voltages.
DigiKey has an easy to use cable filter. Others do too. An option to multiconductor connectors are strain reliefs (like the Skintops currently featured on alliedelec.com's main page). Not as conveniently disconnectable (if that's a word), but then again accidental shock is impossible and it's way cheaper.