period: wheat, brown, and maroon. Fender used various grillcloth and tolex combinations, suggesting that they were using up whatever stock was on hand instead of assigning one combination to one amp consistently. Accomplishments for the company's amplifier division during these years include the introduction of the stand-alone spring reverb unit in 1961, followed by incorporation of the reverb circuit within a combo-amp design with the 1963 Vibroverb. Other changes include the shift of the top-of-the-line model from the traditional Twin to include other models, like the Vibrasonic in early 1960, as well as the blonde Showman in 1961. Fender began using silicon rectifiers to reduce heat and voltage sag caused by tube rectifiers, and introduced an all-new, very complex Tremolo circuit (or, as it referred by Fender, "vibrato"). Blackface The Blackface amplifiers were produced between 1963 and mid 1968 with the earliest blackface piggyback and large combo amps (Twin) having bodies covered in blonde tolex, with the new black control panel. The white control knobs continued briefly before giving way to black skirted "hat shaped" numbered knobs. These amps had new circuitry featuring bright switches. Blackfaced cosmetics do not necessarily mean "pre-CBS" since the CBS company takeover took place in 1965 and amps with blackfaced cosmetics were produced up to 1967. After the buyout the front panels were changed from "Fender Electric Instrument Co." to "Fender Musical Instruments". No real changes were made to the amps until the silver faced amps of 1968 where certain circuit changes made them less desirable than the black faced amps. This affected some models more than others. For example, the Twin Reverb and Super Reverb combos, along with the Dual Showman Reverb and Bandmaster Reverb "piggyback" heads were equipped with a master volume control while other models such as the Deluxe Reverb were not altered in any way except for the change in cosmetics. Silverface cosmetics do not necessarily denote silver face circuitry, however. Leo Fender was notorious for tweaking his designs. During the transitional period from late 1967 to mid-1968, the circuit designs of the Twin Reverb and Super Reverb were altered to eliminate an uncommon but serious oscillation in the signal chain. These changes took some months to finalize, as Leo worked through some designs, and happened after the cosmetic changes. Furthermore, the schematic and tube charts that shipped with these models did not always reflect the actual circuitry. Fender had many