[QuadList] Ampex Mark XV head question

[lee williams]

Have a new Mark XV head on a AVR3 that has about 100 on it. 
 
It starts off quiet, then after about a half hour starts to develop a random whine as the tape is passing through. 
 
I would normally call up the company that rebuilt it, but the last 3 times we have sent something back to them they have not honored there warranty. 
 
Does anybody have any experience with working on a Mark XV ? 
 
Was wondering what the screw with the spring that is close to the brushes adjusts? 
 
I am really hesitant to do anything because this head is making a really great picture, but I am concerned that the whine is cutting down on the life. 
 
Any experience would be appreciated. 
 
Thanks 
 
Lee  
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