A NEW LAST STAGE VALYE

Radio Record, Volume II, Issue 5, 17 August 1928, Page 10

A NEW LAST STAGE VALYE

A NEW valve has been developed by the Philips Laboratcries on the new principle of utilisin~ three grids. It is being designed expressly for last stage audio amplification. This valve has the enormous amplification factor of 100 without adversely affecting the valve’s ability’ to handle a large amount of undistorted power. The Philips B443 handles, it is claimed, three to four times the undistorted output possible from a single grid valve working under similar conditions. Previously last stage power valves have been made of low internal] resistance in order to increase’ the amount of undistorted output that they would handle. This had the effect of causing the A.C. current passins through the loudspeaker to be less at high tonal frequencies than at low, with the result that thes: higher frequencies were glossed over. The special design of the B443 overcomes this without sacrificing the bass register. The B443 is economical in operation for such a super-power valve, the nor-

mal plate current being 12 milliamperes, while the negative grid bias voltage is much less than required. A The filament consumption is but 0. ampere at 4 volts. The plate voltage may vary between 50 and 150, while the mutual conduct: nce or slope is 1.8 m.a. per volt. The valve may be fitted into any ordinary set by connecting an oxtra wire from the B plus terminal to the screw connection provided on the side of the base.