[QuadList] A Little More on Toluene Discriminators in Servos

[chill315 at aol.com]

I have followed the discussion of the solvents that folks use.  I have  
learned a great deal that I never knew.
 
The GREEN tape was included sometimes on the first Ampex 1 inch  machines.  
The 7000 series.  It was a burnishing tape used in head  replacement.  I 
never used it as it would wear the heads very fast.
 
I am wondering what the modifications were to the servos.  I can not  see a 
mod to the Reference discriminator as the machine had to switch between  
several sync sources in normal operations.  Video in during record and  
external during playback.  If it were to go to external at all times,  during 
record the vertical sync placement on tape would not meet SMPTE  specifications 
or if asynchronous, it would float at all times making the tape  unplayable. 
 The two rotary switches on the front of the servo would allow  you to 
override the normal operation and allow you to do this.  
 
The Capstan discriminator was touchy.  If one put the 625 oscillator  
control in parallel with the 525 control it became a fine frequency  control.  In 
our machines the Capstan was critical for use on a machine  that was an 
editing machine.  The servos had to be a close to perfect just  before the edit 
to prevent whips and glitches. It was an easy procedure that  resulted in 
never having a problem.  Just set the discriminators and  oscillators before 
each session.  It took about 2 minutes and the results  were very 
consistent.  We also found the tach position was easy to set if  you used the demod 
out in pulse cross.  We had some of he best edits in the  market.  The only 
time we had a problem with tach phase was when an AVR 2  was used to record 
the edits and one frame edits were made.  There was  something that caused a 
slight phase jump for about a field or two.  It was  never out of the range 
for the TBC but just irked us.
 
Chris Hill
WA8IGN
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