Throughout the 1950s, as prices of capacitors decreased, designers steadily increased their values. The original Williamson amplifier used paper capacitors; by 1952 Kiebert uses electrolytics; the 1955 reference design by Keroes used at least bypass capacitors; the 1961 budget amplifier by Wright employed a total of . Designers of the commercial Bell2200 amplifier (1953) replaced direct coupling of the first two stages with capacitive coupling; the Stromberg-CarlsonAR-425 (also 1953) use a tetrode-mode output stage in an otherwise familiar Williamson topology. Both Bell and Stromberg-Carson modifications further worsened stability, and required additional frequency compensation. Designers of the BogenDB20 (1953) went even further, and combined global and local negative feedback loops with positive feedback in the output stage.
