[QuadList] Got my VR 1200's

[Don Norwood]

Hi Doug:

I think Park assumed that you would be using both machines.  Since you are 
only going to be operating one machine, your air requirement is only about 1 
cfm @ 50 psi.  Therefore, anything that can supply at least that volume will 
suffice.  The original approach used by both Ampex and RCA for systems not 
on "house" air was a compressor that was very slightly oversized and ran 
continuously.  Compressors were made by either Gast or B&G and were oilless 
designs.

For a tank system with intermittent operation of the compressor, the 
variables that come into play (assuming a fixed demand) are the output of 
the compressor and the volume of the tank.  I like a 50% or less duty cycle, 
meaning that the compressor runs no more than half the time.  To do that, 
the compressor must provide 2X the required volume at operating pressure. 
The size of the tank then determines the length of the duty cycle.  In other 
words, a small tank might provide 1 minute on/1 minute off while a large 
tank would provide 5 minutes on/5 minutes off.  Increasing the output of the 
compressor will change the ratio of the on/off cycle but the tank size will 
still determine the total length of the cycle.

There is a chart on the Gast website which helps determine the proper 
combination of all of the above.  Bottom line though is that the tank size 
cannot make up for an undersized compressor.  I agree with Park's sentiment 
regarding the Gast compressors.  They are expensive though, but with 
patience, you can sometimes get them very reasonably on eBay once you know 
what models are acceptable.

Also, be absolutely sure your air is clean, as dry as possible and oil-free. 
Don't use an air hose from your shop that has been hooked up to a regular 
compressor.   Oil is deadly to the air bearings in the head.

Don

----- Original Message ----- 
From: "C. Park Seward" <park at videopark.com>
To: "Quad List" <quadlist at quadvideotapegroup.com>
Sent: Friday, November 27, 2009 9:15 AM
Subject: Re: [QuadList] Got my VR 1200's


> Hi Doug
>
> You'll have fun working on your "science experiment".
>
> Air pressure 55 psi +- 2 @ 2.5 cfm.
>
> I bought a cheap Sears and an expensive Gast. Love the Gast.
>
> Get a ESR meter to check the caps. Around $100. I used shotgun caps  until 
> I discovered that the caps in the 1200 were actually better than  new 
> caps! At least as far as ESR.
>
> THe big caps in the PS could be replaced but they are expensive. I  have a 
> PS guy who has repared sone of mine.
>
> Best,
> Park
>
> C. Park Seward
> 818-535-2747 cell
> 949-679-1870 hm
> Visit us at: www.videopark.com
> Sent from my iPhone
>
> On Nov 27, 2009, at 6:04 AM, "Doug Bingley" <dbingley at rock95.com> wrote:
>
>>
>> Thanks to some assistance from Don Norwood, I received two VR1200B's a
>> couple of weeks ago. Should keep me busy all winter long!
>>
>> Couple of questions:
>>
>> 1. What is normal air pressure and volume requirements for these  beasts? 
>> Can
>> I get away with a really little compressor and a big tank, or do I  need
>> something with a lot of grunt?
>>
>> 2. Normally I recap old equipment as when a cap goes it often takes 
>> other
>> components with it. I will likely recap at the least the power  supplies.
>>
>> I am thinking of going through board by board and replacing 
>> electrolytics
>> before I power it up, but I'm afraid this could damage something as  I 
>> work
>> on the boards. On the other hand I have worked on 70 year old radios 
>> that
>> still function with old caps.
>>
>> What have others experienced?
>>
>>
>> Doug
>>
>>
>>
>> _______________________________________________
>> Please trim posts to relevant info when replying!
>> Send QuadList list posts to QuadList at quadvideotapegroup.com
>> Your subscribe, unsubscribe and digest options are here:
>> http://mail.quadvideotapegroup.com/mailman/listinfo/quadlist_quadvideotapegroup.com
>
> _______________________________________________
> Please trim posts to relevant info when replying!
> Send QuadList list posts to QuadList at quadvideotapegroup.com
> Your subscribe, unsubscribe and digest options are here:
> http://mail.quadvideotapegroup.com/mailman/listinfo/quadlist_quadvideotapegroup.com