You will need
  • - A powerful electric lamp in a cartridge;
  • - multimeter.
Carefully inspect the transformer. On some models of transformer windings are signed on the upper layer of insulating paper and signed the appropriate conclusions. TPP transformers are completely encapsulated green color, they are called military transformermi. They write a brand that's in the book on such a transformerm, and number the terminals of the windings. To find the primary winding of the transformer from the amplifier or the low-voltage power supply is quite simple – it is made of wire of smaller cross section than the secondary winding. To find the primary winding of the low-power transformer from the devices it is possible, having measured resistance of all windings. The winding with the highest resistance will be the primary.
On old tube equipment used the powerful multiple-winding transformers of THANE. Resistance their high-voltage windings differed slightly, and the value of the winding resistance was not difficult to determine which winding is the primary. You can find the primary winding of such transformer, measure the resistance of each winding and take note of the numbers on paper, check also the location of their conclusions. Those windings, the resistance of which tends to zero is a low voltage winding, designed to supply filament cathodes of radio tubes. The remaining coil can be investigated by submitting them to stress.
Plug in a powerful electric lamp for 220V in series with the winding of the investigated transformer and switch in the network received an electrical circuit. Using a multimeter switched to the measuring AC voltage, measure the voltage on the winding of the transformer. After that, turn the power off and explore the other winding. Record the results on paper. In the study of the windings be careful and never turn winding with included mains supply. When a voltage is applied to the coil do not touch the conclusions of the other windings, as they are induced corresponding voltage.
Make the power cable to the fuse holder, install the fuse at a current of 1A.
For this record to locate the coil, which was the highest supply voltage. Turn on the transformer, this winding network by connecting sequentially the multimeter switched to the current measurement. If no load current is less than 30-50mA for transformers with a power of 200-300W may, the primary winding was found correctly.
Disconnect mains supply, disconnect the multimeter from the test winding, switch mode Vollmer. Measure the voltage and record the value obtained on paper.
Measure the voltage on the windings of the cathode was found. If the network voltage is 220-225V it is from 6.25 to 6.35 In, so studied winding is the primary.