The 7025 is a top-of-the-line vintage product equivalent to the 12AX7 and can be used as a direct replacement. At the time, Russia manufactured excellent electronic components for the aerospace industry, and rockets and satellites were among the world's best, employing high-durability, low-noise, high-performance vacuum tubes. (W indicates vibration resistance, and A indicates low noise.) I have confirmed the sound output on an actual device before listing. Please take a look at the photos and consider purchasing.