[QuadList] A Little More on Toluene Discriminators in Servos

[georgenann at aol.com]

Hi Chris,

I have learned quite a bit also about all those solvents. It is interesting, but I guess the bottom line is don't use any of them.  They are dangerous.  During one flap I had about Toluene, the maint. director checked with the building safety guy and he said it is OK to use it in small quantities, in well ventilated areas, which is what was done.  I don't remember if I mentioned the first batch of Toluene CBS ordered was from Cole-Parmer in Chicago.  It was a glass gallon jug full of it and arrived in a cardboard box, although the box did have some cardboard bumpers in it.  I had to hide the jug because if it was broken the whole building would have had to be evacuated.  After that I used the small pint cans from True Value.

Also, I ran all of this past a friend who is a retired chemist who is familiar with polymers, and all that other goo, and he suggested trying "Mineral Spirits".

CBS had some green cleaning tapes early on, they weren't used much by our head guys.  There were 2 guys who did nothing but heads. That was quite a luxury, but it was OK with me especially when it came to setting up "Quad" on them. That was a tedious task and took more patience than I could muster up. They also kept the paperwork on the head hours and did all the ordering.

RE: Ref Disc,  One of the luxuries at CBS was every machine had it's own sync gen which was genlocked to plant sync.  This was true all over the whole building.  Every machine was timed to plant, and if I remember all you  had to do for editing was a slight H adjustment on the editor panel.  The only time there was a non-sync feed was from outside the plant and all that was done was record of it, editing was done from another machine. Also used were lots of framesyncs for outside feeds.

I don't recall there ever being an issue with having to set the cap disc for editing. Occasionally maint. was called to set the cap and head osc's, but that was rare.  I think the cap phase system was so tight it locked right up without the aid of the discriminator. I never thought about your idea of paralling the 625 and 525 pots, that is a good idea, but CBS had a couple machines which were set up for dual standard and there was quite some interchange of servo boards around the plant. I'm sure that would have caused a problem at some point.

I should point out something else.  CBS had about 1000 techs, (I think they are down to about 600 now).  There was a big line between Maint and operation types, although everyone was in the saame union. There were about 7 or 8 different maint. groups. When an op needed help they would call maint. and we would make the fix or adjustments as necessary.  If an op tried to make adjustments he would get his pee pee spanked! (Especially if he screwed something up). I only rolled a tape machine on air once, and it never made air, but that's another story. I never cared for operations, not interesting enough. 

Another mod just came to mind, that is there was one pot in the servo, I don't remember it's number but I think it was called "Capstan Gain" or something to that effect.  If it was turned up more that about 50% the cap wouldn't lock or would tend to oscillate. Turns out that the cap system was designed for monochrome. With the color mods there was an improper diameter ratio between the cap motor and the cap wheel. This put the proper cap speed slightly out of range of the servo, or at least close thereto. I think Arnie Ferolito came up with the fix for it which was done by the CBS machine shop (Another Luxury).  They turned down the cap pulley wheel and put a sleeve on it making it a bit larger, turned it to size and that made it happy.

This was a very long time ago, I may get my membership in the CRAFT club revoked for this one.

Another thought, I wonder if anyone has a fix for a broken cap drive belt?  There was a box full of them when I left CBS, but they do break and they may be hard to get.  I don't think rubber bands would do the trick, but if all you are doing is playback there may be a cheap solution.

73,

George Keller







-----Original Message-----
From: chill315 at aol.com
To: quadlist at quadvideotapegroup.com
Sent: Sun, Jan 24, 2010 9:33 am
Subject: Re: [QuadList] A Little More on Toluene Discriminators in Servos


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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