WHAT CAUSES DISTORTION?

Ellesmere Guardian, Volume XLV, Issue 3175, 9 December 1927, Page 6

WHAT CAUSES DISTORTION?

The seemingly endless variety of causes in this regard may appear discouraging, nevertheless modern amplification systems permit of relatively perfect reproduction, implying the conquest of each one of the possible causes of distortion. They are in the main caused by defects as follows:— 1. Antenna or aerial system — (a) Too long, causing overloading of detector tube with sets lack- ■ ing efficient and effective radio frequency amplification control. (b) Too short an aerial, requiring the over-working of the radio frequency amplifier. 2. Radio frequency amplifier— (a) Regenerative, or near regenerative. (b) Incorrect grid or plate voltages. (c) imperfectly synchronised circuits. (d) Wrong type of tubes.' (c) Magnetic coupling with alternating current elements of power supply, or with radio transformers. 1 (f) Insufficient filtering or inadequate by-passing of power supply leads. 3. Detector — (a) Overloaded (1) by radio frequency amplifier; (2) because of incorrect grid voltage. (b) Over-regeneration. 4. Audio amplifier— (a) Wrong type of tubes. (b) Incorrect grid or plate voltage. (c) Tube output impedance incorrect for load impedance. (d) Audio frequency regeneration due to (1) magnetic coupling between transformers or coupling devices; (2) Conductive coupling through imperfectly by-pas-sed power leads; (3) Acoustic or mechanical coupling of tube elements with resonant cabinet; ' (4) Magnetic coupling with power circuits; (5) Acoustic or mechanical coupling with reproducer. In order to check which of these is responsible for the ultimate distortion of the output of the loud speaker, an eliminating process is necessary, which can in most cases be carried out by the trained radio expert. There are certain definite rules to be obeyed, |iowever, in the construction of the average receiving set, which to a certain degree ensure the elimination of the more ordinary causes of distortion. The most frequent trouble is the use of the wrong valves in the audio-frequency . end of the set, particularly the last valve. Unless the last valve, which feeds into the speaker, is capable of adequately handling the amount of current variations impressed upon it, it will counteract adversely any precau- ■ tions which may have been taken in the . preceding stages of radio, detection • and audio frequency amplification. 1 Valves suitable for this last stage that i will give excellent results are U.X.171, ' U.X.112 and Mullard power valve.