[QuadList] Capstan questions

[chill315 at aol.com]

Interesting thoughts.

First this was a record function to make black time coded tapes for editing.  This was with the same house sync and house time code generator.  Thus all are running to house references.  At 15 inches per second 32 minutes gives approximately 28,800 inches of tape.  When two machines went for different lights of time it got me interested.  

The playback showed different capstan error so thus the only thing I can come up with is a slight difference in the diameter of the shaft.

Chris Hill

> On Sep 23, 2014, at 11:33 AM, Dave Sieg <dave at zfx.com> wrote:
> 
> Chris:
> My recollection is that all quads capstan servos in playback basically lock the control track to house reference sync.
> In record they lock to a fixed reference, which could presumeably be mis-adjusted to move slightly
> more or less tape through the machine per unit time.  Nonetheless, in playback, the capstan
> servo would have to compensate, thus moving the tape at the slightly fast or slow speed in order
> to get the control track to phase and frequency lock to house reference.
> So I can see how a slightly mis-adjusted record speed might use a few more or less feet of tape,
> but that would be compensated for in playback.  I can't see how if both machines stayed locked
> they would result in different record times.  I'd double check the timecode systems to be sure
> they were not reading something wrong. Timecode can do funny things while a machine is locking.
> But once running with no breakup they should be in lockstep with the house sync at least vertically.
> Then again, I've slept a few times since I was "current" in quad maintenance, your mileage may vary!
> Dave
> 
> 
>> On Tue, Sep 23, 2014 at 10:41 AM, Chris Hill via QuadList <quadlist at quadvideotapegroup.com> wrote:
>> 
>> 
>> 
>> ---------- Forwarded message ----------
>> From: Chill315 at aol.com
>> To: quadlist at quadvideotapegroup.com
>> Cc: 
>> Date: Tue, 23 Sep 2014 10:41:29 -0400
>> Subject: Capstan questions
>> I always wondered what the tolerances were for the sizes of a capstan.  Reason for the question.
>>  
>> I was remembering that on a VR-1200 the same tape played on two different machines would show a positive or negative capstan error.  Then we time coded the same tape on the two machines and there was a difference in the final time code number by several seconds.  Thus there had to be a small difference over the 32 minutes of tape. 
>>  
>> Now capstan sizes.  The VR series used basically the same size capstan.  As well as the AVR-2.  the AVR-1, ACR-25 used the vacuum capstan that was substantially larger.  As I never inspected an AVR-3, I can only look at the pictures and surmise that it was similar to the AVR-1 capstan.  What were the tolerances?  Were the vacuum capstans a variable that enters into the equation?  I only worked with an ACR so do not have the experience with the AVR-1.
>>  
>> Does anyone have insight for this set of questions?
>>  
>> Then the last question is we all know that the tape does have an abrasive quality to it.  Being that the back side touches the capstan and front side touches the roller, the tape would not wear down the capstan like an audio head or guide.  Yet I have seen a number of capstans that show a polished portion that could be taken for wear.  Has anyone ever had to replace a capstan due to excessive wear?
>>  
>> Chris Hill
>> WA8IGN
>> 
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> 
> 
> 
> -- 
> Dave Sieg
> www.zfx.com
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