The image below (recorded in 1966) displays a vacuum guide error. The heads have been moved back from the tape, lessening the geometry. Ampex VTRs with AMTEC processing could remove guide error electronically, but effectiveness was limited (the error in the example above would be too severe for AMTEC processing to correct it).
During playback of 2” Quadruplex tape, a pneumatic guide is used to adjust the head-to-tape spacing. If the guide is positioned further away from the heads than it was during recording, a distorted image will result from the difference in head geometry. Normally, TBC electronics in the playback machine will attempt to correct this problem, so the demodulated output from the machine is useful for adjustment during setup of the machine.
Can it be fixed?
A manual adjustment to the vacuum guide can be made to help approximate the position needed for proper playback . However, a digital TBC will be able to remove this error entirely. The analog AMTEC processor was also used to lessen this error, but it did not have as much correction range. Late model Quadruplex machines had an automatic guide servo that removed the error, as well.