Yes you can use any classic Mac 9" CRT (except the Color Classic) to replace any other. However, it sounds more like you have some adjustment issues, which members of this forum can be of further help in diagnosing and repairing. Keep in mind if it is an adjustment issue, something caused it to go out of adjustment, most likely shrinking capacitors and other failing analogue board parts. This is a good place to start: http://68kmla.org/files/