[QuadList] VR-3000 History

[Don Norwood]

Hi Chris:

Yes indeed.  The compliance arms were changed fairly early and were a major 
improvement.  The upgrade kit manual is dated '70.  For those not familiar 
with the machine, the transport is essentially a constant tension design, 
and when it is operating normally, capstan current is basically zero as the 
reel servo is driving the tape at seed.  When external forces impact the 
machine (movement of the deck while being carried or worn in the back-pack 
configuration for instance), then both the capstan servo and tension (reel) 
servo may be required to control speed.  The reaction time of the capstan is 
much faster than the reels due to the inertia of the reels.

The inputs to the tension servo come from two compliance arms, one for each 
reel.  The original design used strain gauges which varied resistance 
according to their position.  The resolution available from this approach 
was not sufficient to adequately and rapidly control the tension.  The 
solution was to change to a variable capacitance approach.  A 500 kHz signal 
was generated and the compliance arms were attached to large plates whose 
spacing changed as the arms were moved, resulting in a wide capacitance 
shift which in turn controlled how much of the 500 kHz signal was passed 
thru the circuit.  This approach gave much greater resolution than the 
resistive system, and greatly improved the operation of the tension servo.

Don Norwood
Digitrak Communications, Inc.
www.digitrakcom.com

----- Original Message ----- 
From: <chill315 at aol.com>
>
> There were update kits available that did things like compliance arms and 
> other stuff.  Maybe we can get a history of the changes.
>
> Chris Hill
>
> On Aug 13, 2012, at 12:25 PM, "Don Norwood" <dwnorwood at embarqmail.com> 
> wrote:
>
>>
>> I've been restoring another VR-3000, and this one is diffeent from any of 
>> the others that I've done in the past.  From component date codes, it 
>> appears to have been made in early '76.  The unusual aspect of this 
>> machine is that it includes many of the features of a VR-3000B.  It does 
>> not have the additional audio circuitry of the "B", but it does have dual 
>> speed operation and the connector for the external TBC-900.  All of this, 
>> including the TBC interface card, appears to be original factory 
>> assembly.
>>
>> I'm hoping Bill Carpenter or others can detail the evolution of the 3000. 
>> I didn't realize that the external processing was available prior to the 
>> "B". The VR-3000B manual I have is dated '77, so I assume this machine 
>> may have been made just prior to the B's introduction.
>>
>> Always good to learn more about the history of these amazing machines!
>>
>> Don Norwood
>> Digitrak Communications, Inc.
>> www.digitrakcom.com
>>