From robrobinette.com
With a two prong power cord and no death cap the chassis voltage will float since the power transformer primary is not connected to the chassis. A normally functioning amp's floating chassis will not be electrified by 125v no matter the orientation of the power plug in the wall socket. Floating chassis are not used in tube amps for two main reasons: A floating chassis will provide no RFI noise protection and there is no protection from a hot AC power transformer primary wire coming loose and electrifying the chassis to create an extreme shock hazard. The now mandatory third power cord wire, the safety ground to chassis, mitigates this risk by shunting any stray voltage and current on the chassis straight to ground. The safety ground also provides RFI noise protection.
The death cap serves no safety purpose. The death cap provides only AC RFI ground, not a safety ground. With the ground switch in its usual quietist position with the chassis and death cap connected to neutral (ground), if a loose wire electrifies the chassis the death cap will limit AC flowing through it to 2.4ma, the rest of the current will flow through anyone that touches the chassis. Of course no DC can flow through the death cap to ground so again, it will flow through anyone that touches the chassis.
