[QuadList] History - what is the REAL story

[Chill315 at aol.com]

Head switching was done on the back porch by AMPEX.  This was done  because 
the AMTEC used the leading edge of sync to generate an error signal for  
the delay line.  If you did not do this, the first line of each head pass  
would be pulled off to one side or the other.  We have all seen tapes that  
have this phenomenon.  
 
RCA did sync tip switching.  I do not have a book on the ATC system to  see 
what was going on there.  I have a TR 4 manual but it is the bare bones  
and no TBC information.
 
VR-1000 would show a wider H blanking on the switch line.  It was  
something that was cured in the later machines.  
 
The RCA machines through the TR 3, 4, and 22 would have the VARIBLE EQ  
switch on the de mod that would allow the machine to playback an early TRT 1 A  
special color format.  This was to compensate for the 9.54 db pre emphasis  
of the video.  The deviation was close enough to LO BAND COLOR that the  
levels would just be a little off.
 
If the tape were a dub of a color signal that had used the early heterodyne 
 playback system, then the ATC had to be turned to NON PHASED COLOR.  
 
I hope that gives a little bit of information.
 
Chris Hill
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