LESS DISTORTION

Ellesmere Guardian, Volume XLV, Issue 3228, 15 June 1928, Page 6

LESS DISTORTION

VALVES FOR BEST RESULTS.

As a rule, two stages of audio frequency amplification are sufficient to give satisfactory volume for iiome use. Most valve manufacturers advise that UX2OIA tubes deliver tlic greatest amount of undistorted output when operating at 135 volts, at which voltage this type of valve delivers 55 undistorted milliwatts when biased with 9 volts of "C" battery. At 90 volts of B battery supply the same type of tube passes a maximum of 15 undistorted minniwatts when correctly biased with a 4|-volts C battery. Many dealers disregard the C battery, which still cuts down on the undistorted output and in the attempt to get greatest volume the filament rheostats are turned around to the point where the valve becomes overloaded. This overloading affects the quality of reproduction and such overloading results not only in distortion in the sounds produced but also in the production. of most disagreeable rasping or rattling sounds. The semi-power tube UXII2, operating with a potential of 90 volts B battery with 6 volts ■ C battery imposed delivers 40 undistorted minniwatts and when used with 135 volts B battery, and 9 volts bias battery delivers 120 undistorted minniwatts. At 90 volts we have sufficient power output for the ordinary home use and this tube draws 24 milliamperes of B battery current, whereas valve type 201 A draws 2 milliamperes. This undistorted output does not mean that the UXII2 will deliver two or three times as much undistorted output, and when the B and C batteries are of correct value your ears- will detect the difference and you will say that is how radio reproduction is wanted within the home. The UVII2 is known as a semi power tube, while TJXI7I will deliver still more undistorted output. The ideal place for the UXI7I type of valve is in the last stage of a three-stage amplifier because of its low amplification construction of 3 against Bin the UXII2. Unfortunately, there are radio receivers upon the market employing three stages of audio amplification on which provisions have not been made for employing or accommodating UXI7I power tubes which require a rather high C battery, usually from -22 i volts to 45 volts. Study the .characteristics of these semi-power and power tubes, and you find that they will improve the performance of any radio se,t because they do away with overloading. The radio instrument of to-day is an instrument * for undistorted volume and good tone, not as in the volume, undistorted and noisy. With the careful adjustment of the B battery voltages and the use of the above-mentioned valves, perfection in radio broadcast reception can be obtained.