Characteristics of Output Transformers

The paper deals with the operating characteristics of the Output Transformer, which are developed in terms of the known speaker, tube and transformer constants. In the first part of the paper the general formula for the speaker current is developed and the effect of varying the transformer constants shown. The turn ratio of the transformer for maximum speaker current is considered in relation to the commonly used impedance ratio formula. The limitation of the impedance ratio formula is then pointed out and limits set for its general use. The general form of the current frequency characteristic for exponential horns and dynamic cone speakers is then obtained and a general method for matching the speaker to the output tube is given. In the latter part of the paper, curves are given to show the results obtained in the mathematical part of the paper. The curves also include the results of tests made to check the fundamental formula. The effect of the turn ratio on the form of the current frequency characteristic is shown and a method of using the turn ratio of the output transformer to match the speaker to the output tube is given. A perfect transformer is also compared with a good commercial transformer and the general effect of the leakage inductance and the self capacity of the transformer shown.