Modern driver magnets are almost always permanent and made of ferrite, alnico, or, more recently, rare earth such as neodymium and samarium cobalt. Electrodynamic drivers were often used in musical instrument amplifier/speaker cabinets well into the 1950s; there were economic savings in those using tube amplifiers as the field coil could, and usually did, do double duty as a power supply choke. A trend in design — due to increases in transportation costs and a desire for smaller, lighter devices (as in many home theater multi-speaker installations) — is the use of the last instead of heavier ferrite types. Very few manufacturers still produce electrodynamic loudspeakers with electrically powered field coils, as was common in the earliest designs; one of the last is a French firm. When high field-strength permanent magnets became available after WWII, alnico, an alloy of aluminum, nickel, and cobalt became popular, since it dispensed with the problems of field-coil drivers. Alnico was used almost exclusively until about 1980, despite the embarrassing problem of alnico magnets being partially degaussed (i.e., demagnetized) by accidental 'pops' or 'clicks' caused by loose connections, especially if used with a high-power amplifier. The damage can be reversed by "recharging" the magnet, but this requires uncommon specialist equipment and knowledge.