Cornell 18/20 Head Amplifier

Channel One: Hi & Lo inputs Volume Tone Channel Two: Hi & Lo inputs Volume Tone Switch: 18/20 (Rectifier) Mains (On/Off) Class A Push pull Cathode bias. Valve Complement: ECC83 (x2) EL84 (x2) GZ34 (x1) Output: High 20 watts Low 5 watts 8 & 4 ohms jacks Contains the Cornell 'Cream-box'

The Cornell-Plexi 18/20 is made to the basic circuit of the PA20 Plexi panel which was produced in the 60s. Additional Cornell design features like the switchable valve rectification and power reducer are fitted as standard.
Complementary push-pull class "A" output has been used in many renowned amplifiers throughout the history of guitar amplification. The problem with this basic circuit, which has remained common to all manufacturers with some minor differences, was one of unequal current flow through each output valve and unacceptable crossover distortion. At high output levels the problem is accentuated and results in a fuzzy sound.
We have corrected the design and resolved the problem by balancing the output and reducing the crossover distortion. This results in a much smoother sound at high output levels, the output having very little crossover distortion. The difference can be seen and measured on an oscilloscope.
We have encapsulated the components and called it the Cornell-Cream Box which describes the output tone. We now use this circuit in all of our complementary Class "A" push-pull output designed amplifiers.