A switch mode power amplifier includes a transistor responsive to input signals above 1. The ballast preferably is of the type having multiple input voltage taps on the primary coil; in such cases, the electrical positioning of the thermal protector in series with the secondary coil causes the wiring assembly of the thermal protector to be independent of the primary coil input voltage tap used in a particular application. The buoyancy adjusting material is sufficient to give the article overall a positive buoyancy so that it will not sink to the seabed, and is distributed unevenly along the length of the article so as to create regions of negative buoyancy. A control detects a short circuit on the aircraft DC bus.