vacuum-tube circuit

例句：

1. 1. This vacuum tube circuit is used to amplify audio signals.
   这个真空管电路用来放大音频信号。
2. 2. The vacuum tube circuit was the first electronic device invented by Edison.
   真空管电路是爱迪生发明的第一种电子装置。
3. 3. The vacuum tube circuit was used in radios and televisions before transistors were invented.
   真空管电路在晶体管发明之前，被用于收音机和电视机中。