[QuadList] Capstan Size Modification

[georgenann at aol.com]

-----Original Message-----
From: Chill315 at aol.com
To: quadlist at quadvideotapegroup.com
Sent: Mon, Jan 25, 2010 8:51 am
Subject: [QuadList] Capstan Size Modification


George
 
Interesting that CBS would try to turn the capstan.  The diameter was set for monochrome standard at 60 Hz.  The color standard is 59.94 Hz.  This is less than 1 one hundredth of a percent difference.  The size of the capstan determines the length of tape that is pulled through per revolution.  
 
Hi Chris,  I didn't mean the capstan it'self, but the pully wheel connected to the capstan where the belt drives the capstan.  Apparently the window of the servo was not great enough to compensate for the color speed change.

The SMPTE RP for the layout of tracks on the tape is what is critical for interchange.  There has to be the correct distance between tracks.  The angle of the track from vertical.  The distance from the track to the position of the control track head.  The placement of the Vertical sync on the tape with the frame pulse.  Even the distance to the erase and audio heads.  There is a shape that is required called the canoe. Right. there was no change in any of that.  Also RE: the canoe, there was a "Puffer" on the ACR's which blew a small amount of air into the entrance end of the "Canoe" because the point of the "Canoe" was very sharp and the oxide would come off in a thread shape.  There is also something similar on the AVR-1's, I seem to remember or maybe it was near the Vac COl, I don't remember for sure.  Maybe you could shed some light on it.
 
Fortunately there is enough slop in the servos to take into account the miniscule difference in the master sync generators used during record and playback.  Think of video tape as a mechanical frame sync.  Because the capstan and heads compare the off tape sync to the house sync they will adjust the speed to compensate.  
 
Regarding the capstan belt.  I have never had to replace one.  The never broke on the machines that I had.  I did look at one when the capstan was pulled and I took the cover off just to see it.  I did replace the capstan motors on an AVR 2 that was damaged in a fire so that was an easy fix.  We thought about rebuilding the shafts but found out that the diameter was so critical we could only buy new. If my memory serves me correctly that was a DC motor with a built in tach wheel, no belts??

IF I were you I wuld go out and buy some lottery tickets, CBS went through many belts.  There was even a torque screwdriver in the shop used to set up the proper tension on the belts. 

73,

George Keller
 
Chris Hill
WA8IGN

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