The problem in the vibrato channel may not be due to a faulty tube. You can check this by swapping some of the preamp tubes, to see if the trouble moves with the tube.

The 7025 is a military-rated 12AX7A. You can substitute one for the other without problems. If you want less gain, and more headroom, you can try 12AU7 or 5751 tubes as well.

The circuits around preamp tubes allow them to bias themselves. You don't need to adjust anything.