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<DIV><FONT size=3>Hi Chris:</FONT></DIV>
<DIV><FONT size=3></FONT> </DIV>
<DIV><FONT size=3>You are partially correct. What you are thinking about
is Module 13 which is standard. It contains the dropout detector, the
demod input switching, and the circuitry for inserting the peak white reference
pulse from the AFC system. However, the two AFC modules were separate and
optional.</FONT></DIV>
<DIV><FONT size=3></FONT> </DIV>
<DIV><FONT size=3>The "real" DOC requires the addition of Module 16
which is what appears to be installed in this machine. This
is a delay line which delays the RF by one line and then subsequently feeds
it back to module 13 where it is substituted for the DO.
However, if the optional delay line module is not installed, then a fixed level
as you described is inserted by the switch.</FONT></DIV>
<DIV><FONT size=3></FONT> </DIV>
<DIV><FONT size=3>So there were two "levels" of DOC from Ampex, the freebie that
you recall and then a "real" one as installed in this machine. I use the
quotes with "real" because the design obviously did not provide properly phased
video for the dropout. That's what led to the market for the 3M and Merlin
(and others?) DOC's which delayed video instead of RF and then matched it to the
proper phase.</FONT></DIV>
<DIV><FONT size=3></FONT> </DIV>
<DIV><FONT size=3>Don</FONT></DIV>
<BLOCKQUOTE
style="PADDING-RIGHT: 0px; PADDING-LEFT: 5px; MARGIN-LEFT: 5px; BORDER-LEFT: #000000 2px solid; MARGIN-RIGHT: 0px">
<DIV style="FONT: 10pt arial">----- Original Message ----- </DIV>
<DIV
style="BACKGROUND: #e4e4e4; FONT: 10pt arial; font-color: black"><B>From:</B>
<A title=Chill315@aol.com href="mailto:Chill315@aol.com">Chill315@aol.com</A>
</DIV>
<DIV style="FONT: 10pt arial"><B>To:</B> <A
title=quadlist@quadvideotapegroup.com
href="mailto:quadlist@quadvideotapegroup.com">quadlist@quadvideotapegroup.com</A>
</DIV>
<DIV style="FONT: 10pt arial"><B>Sent:</B> Thursday, December 10, 2009 4:11
PM</DIV>
<DIV style="FONT: 10pt arial"><B>Subject:</B> Re: [QuadList] Ampex VR-1200 on
ebay-in Apalachin, NY</DIV>
<DIV><BR></DIV><FONT id=role_document face=Arial color=#000000 size=2>
<DIV>Don</DIV>
<DIV> </DIV>
<DIV>The AFC and Bare Bones DOC were included in all the machines at some
point in manufacture. The DOC was part of the AFC design. It was a
freebie as I put it. The RF signal that was inserted back into the
picture during a drop out was the frequency of blanking. This frequency
was used as it was the one that the AFC could clamp to a know point in
the video. Ampex did not use sync for a good reason. Sync levels
varied by a few between sources and thus with 100 IRE of video but different
levels of sync, the video level would change at the output of the de mod if
you clamped at sync tip prior to modulation.</DIV>
<DIV> </DIV>
<DIV>At least this is the way that I understood. Can someone verify this
or am I out to lunch on this theory?</DIV>
<DIV> </DIV>
<DIV>Chris Hill</DIV>
<DIV>WA8IGN</DIV></FONT>
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