See the data sheet for turns ratio when using different configurations. For the transformer in Figure 3-1, the voltage on the primary and secondary sides has been marked. The turns ratio (abbreviated as TR) is proportional with the voltage ratio. Table 3-1 show the basic characteristics of the transformer.

Figure 3-1 Step-Up Transformer From Peavey® (Auto Match II 400W 18737)

For the transformer in Figure 3-2, the voltage level is not marked on one side (4 Ω, 8 Ω side). Two methods can be applied to determine the turns ratio. First, a 300-W transformer. If 4 Ω is the primary configuration, and 300 W must be reached when the input is about 34.6 V (according to Equation 2), the turns ratio can be calculated as 34.6 / 70.7 = 1 / 2.04 under 4 Ω, 70 V configuration. If 8 Ω is the primary configuration, the corresponding voltage level is about 49 V, and the turns ratio for 8 Ω, 70 V is 49 / 70.7 = 1 / 1.44. The other option is to connect a certain resistor (say 40 Ω) to one side and test the equivalent resistance on the other side. If connecting 16 Ω to tap 70 V, and measuring the resistance between tap "4 Ω" and tap “Com” is measured as 3.84 Ω, the relevant turns ratio is 2.04 according to Equation 1.

Figure 3-2 Step-Up Transformer From EDCOR® (EA300)

For the step-down transformer in Figure 3-3, the turns ratio can be determined by measuring the equivalent resistance. In this case, a 70-V system was considered. For the primary side, the voltage and power is known. And for secondary side, the reference resistive load is known. Suppose input power P (10 W, 5 W, 2.5 W, 1.25 W or 0.62 W), primary voltage U₁ (70.7 V), equivalent resistance, R₁, and secondary side voltage is U₂ (unknown), or R₂ (4 Ω or 8 Ω). If power losses are ignored, the power on both sides should be the same.

The turns ratio was determined using Equation 10.

Figure 3-3 Step-Down Transformer From Peavey® (330-040) (a)

Figure 3-4 Step-Down Transformer From Peavey® (330-040) (b)