[QuadList] Ampex AST heads and CMC DPT heads--what's different?

[Tim Stoffel]

On Fri, 2010-05-07 at 20:56 -0700, Ted Langdell wrote:
> Yes... AST was an Ampex trademark, and DPT "Dynamic Parallell
> Tracking" was apparently a TM of CMC.
> 
> 
> I'm just curious to know what's different... and the story behind it.
> 
> 
> Ted
> 
   An AST head has a single, planar bimorph crystal with the head tip
glued to the end of it. When the head tip moves up and down with the
bimorph, it describe a (small arc), with the angle of the head tip
contacting the tape changing as the head moves.
   CMC determined that the aforementioned angle change hurt the
performance of the head. So, they added a cantilever to the bimorph
crystal that actually carries the head tip. Now, when the bimorph moves
up or down, the cantilever adjusts in such a way as to keep the head tip
perpendicular to the tape.
    In general, AST and DPT heads are interchangeable. However, some
machines required that some pots in the AST servo be preset to a certain
value before changing head types, to get the servo 'close enough' to be
stable for alignment.

Tim Stoffel