[QuadList] Cap Disc

Wed Jan 27 11:30:45 CST 2010

Yes Trevor, I must have passed a brainstone earlier, in rec even under servo/tach control the dia of the cap is a factor.  Tnx fer the wakeup.

Also if I remember correctly, at least with the Ampex machines the cap actualy freeruns momentarily in an assemble edit.  Also I think this is the reason that at least at CBS insert edits were never used, always used insert edits.  I think this stigma has stuck around for some time, even though insert edits are now OK with the newer machines.

Where are you in the UK?  Was there a while back, the wife took a spill and busted a bone in her hip and she was in the hosp. for couple weeks in London.  I couldn't believe the care she received there, it was terrific.  She was in St. Mary's at Paddington. (She screwed up a couple great cruises).  She is OK, verticle walking OK with cane for time being for bal.  Will be back soon.

Tnx Agn,

George Keller

-----Original Message-----
From: Trevor Brown <videovault at sky.com>
To: 'Quad List' <quadlist at quadvideotapegroup.com>
Sent: Wed, Jan 27, 2010 12:16 pm
Subject: Re: [QuadList] Cap Disc

Can I just throw in an hand grenade

Yes the capstan is locked to the head in record, so tape speed is a product of capstan diameter only
The dimension stability of tape is not good as temperature changes so does its length so the track measurements change
Hence helical scan required AST before slo-mo came along just to have interchange or to play back the tape  recorded at a different temperature
Remember the 7900, machines and poor interchange

Worst case in quad is an assembly edit, where you change from control track controlled speed to a speed set by the diameter of the capstan
Hence the pip on the ramp on RCA machines, push the toggle and it needs to hold for 4 seconds or you edit might fall apart, (set Capstan free run)

Trevor Brown
UK

From: quadlist-bounces at quadvideotapegroup.com [mailto:quadlist-bounces at quadvideotapegroup.com] On Behalf Of georgenann at aol.com
Sent: 27 January 2010 16:40
To: quadlist at quadvideotapegroup.com
Subject: Re: [QuadList] Cap Disc

-----Original Message-----
From: Don Norwood <dwnorwood at embarqmail.com>
To: Quad List <quadlist at quadvideotapegroup.com>
Sent: Tue, Jan 26, 2010 10:42 pm
Subject: Re: [QuadList] Cap Disc

New replies in GREEN below.....

----- Original Message ----- 

From: georgenann at aol.com 

Subject: Re: [QuadList] Cap Disc

-----Original Message-----
From: Don Norwood <dwnorwood at embarqmail.com>

My post about changing the speed of the capstan was referring to your description of what was done to the pulleys on VR-2000 or 1200 machines.  Unless I'm missing something, that would change the tape speed, which in turn changes the video track specifications.

Well, it might change the tape speed if it weren't for the servo, it just put it into a slightly different range, one the servo seemed to like a little better.

Agreed, but ONLY for playback where the capstan speed is controlled by the servo.  If the machine is for playback only, no problem, although I would have guessed that an electronic modification would have been much easier.  My concern would be in record, where the capstan is fed a fixed frequency, and therefore the speed is affected by the mechanics.  The servo has no way of knowing what the actual velocity of the tape is in record.  If it has been changed by a mechanical modification, then the track alignment will be non-standard.

The capstan is always under servo control.  It is derived from the head tach. The head is locked to V, either re or incoming video.

Nobody ever came up with an electronic mod for this, I don't know why, will have to think about this.

I remember those damn round chips in bd 9, 10.  I whish they had left them alone, they made it hard to get a scope in there to troubleshoot. Board 14 was reframing?? I don't recall having any problem with it so left it alone.

Yes, 14 is mostly reframing.  After many years, the relays on the board can be problematic and cause trouble with normal servo operation.

You sure have a great memory, you should write a book on the history of the servo, kind of like the big Rolex or Vibroplex history books. (Just kidding).  Tnx fer the info it is interesting.  I didn't get into the machines till the 70's.

I got into the machines in the early 70's, and it's not my memory that's great, it's just that I have collected as much reference material as possible.  Since I still work on these, some things are more easily recalled than others, but I still have to look up a lot of stuff!

Don

Lucky guy, it sure was fun.

Tnx Agn

DE GK

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