A Method of Neutralizing Hum and Feed-Back Caused by Variations in the Plate Supply

A method is described whereby hum and feedback can be reduced in multistage screen-grid resistance-coupled amplifiers. By the method described it is possible to reduce degenerative and regenerative feedback and hum. The principle involves using the screen grid of a multigrid tube in such a manner that it produces a variation upon the grid of the followling tube substantially equal to and out of phase with the variation appearing at that grid directly through the plate-circuit resistor. The two thus neutralize out. The theory giving the conditions under which neutralization takes place is described. Experimental data prove that such neutralization does take place. Typical graphs giving the conditions for neutralization using a 6C6 tube are given.