| 摘要 |
PROBLEM TO BE SOLVED: To provide circuit constitution for preventing, by simple constitution, direct current magnetization of an output transformer in a vacuum tube amplifier in which a power amplifier circuit is composed of a single circuit. SOLUTION: A direct current magnetization prevention circuit for preventing the direct current magnetization of an output transformer 3 attached to the vacuum tube amplifier 1 is provided with a first choke transformer 17a and a second choke transformer 17b having the same capacity, and a variable resistor 18. By adjusting a resistance value of the variable resistor 18, B power supply voltage (for example, 300V) of a power supply circuit part 4 to be applied to one end of a primary side coil 3a of the output transformer 3 is divided to coincide with output side voltage (for example, 290V) of a power amplifier circuit 9 to be applied to the other end of the primary side coil 3a of the output transformer 3. Potentials at both ends of the primary side coil 3a are made equal to cause plate current of a power output vacuum tube 8 to flow via the choke transformers 17a and 17b and the variable resistor 18. Direct magnetization of a transformer core 3c of the output transformer 3 can be prevented. COPYRIGHT: (C)2009,JPO&INPIT
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