Vacuum tubes, called valves in England, were the standard in home-audio systems until the advent of the transistor in the 1950s. Tubes can be used to increase a device’s amplification, which translates into more volume in a high-fidelity amplifier. In particular, tube amplifiers are renowned for their warmer sound when compared to amplifiers with solid-state circuitry. Two of the best-known makers or tube amplifiers are Healthkit, which sold amplifier kits to home-audio hobbyists in the 1950s and ’60s, and McIntosh, whose amplifiers, pre-amps, and tuners were considered the gold standard by many audiophiles during the same decades.