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| When building power supplies, selecting the proper size transformer can be a problem. Here are a few simple pointers to use. |
| 1. Know how much total current the circuit will draw |
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Add up all the various circuit currents. Add 10% safety factor to the required transformer current rating. Use a transformer rated at the required current draw or higher. Never use a transformer rated less current than required.> |
| 2. figure out the required transformer voltage |
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What voltage is required at tube circuits (B+). Add 20 volts to compensate for aprox loss through filtering circuits. Multiply the desired DC voltage by .707 to find the aprox required transformer voltage. Double the required voltage for a full wave tube rectifier circuit. |
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8 - 12AX7 amplifier stages @ 4ma each 12AX7 = 32ma add 10% safety factor = 35.2ma desired DC high voltage = 300 volts B+ add 20 volts for filter circuit loss = 320VDC at rectifier output 320 (VDC) X .707 = 226VAC transformer voltage full wave transformer secondary = 452VCT (volts center tapped) |
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FIND A TRANSFORMER THAT IS A CLOSE MATCH Select a transformer that has a voltage close to what you need. The current rating of the high voltage secondary should be what you need or higher. Never use a transformer rated at a lower current than what you require. Vacuum tube audio circuits are not voltage critical. If your circuit calls for 300VDC and you wind up with 280VDC or 320VDC, the circuit will still perform well. Circuits using a voltage regulator tube will still provide the required regulated voltage over a wide range of voltage if properly designed. NOTE The transformer primary voltage has no effect on the secondary calculations, primary voltage simply matches your power voltage |
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TRANSFORMER - TRANSFORMER - TRANSFORMER - TRANSFORMER - TRANSFORMER - TRANSFORMER - TRANSFORMER - TRANSFORMER
TRANSFORMER - TRANSFORMER - TRANSFORMER - TRANSFORMER - TRANSFORMER - TRANSFORMER - TRANSFORMER - TRANSFORMER
TRANSFORMER - TRANSFORMER - TRANSFORMER - TRANSFORMER - TRANSFORMER - TRANSFORMER - TRANSFORMER - TRANSFORMER