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[AMPS] Recycling filament

To: <amps@contesting.com>
Subject: [AMPS] Recycling filament
From: measures@vc.net (Rich Measures)
Date: Fri, 27 Jun 97 07:39:42 -0700
>> >I have to agree with Peter, I can't imagine a 723 being a "good 
>> >choice" for an IC near strong RF fields. 
>> 
>> Instead of trying to imagine, why not try trying to see if it works, Mr. 
>> Rauch?
>
>I've had bad luck with 723's unless they are in a well shielded 
>area and everything is bypassed quite well.

I believe that the circuit designer designs his own luck.  

>The shielding and layout is probably more important than the 
>specific value of bypass component, especially since the series 
>resonant frequency varies greatly with different components and lead 
>lengths.

That's why solid state RF amplifiers typically use multi-values multi-C 
DC supply RF byassing.  That's why I used it in my 723-based screen 
supply.  I know that if you have RF on V-in, you are IN trouble.  

>Time would be better spent describing a proper layout and 
>bypassing, especially since Peter is right. The 723 is very 
>sensitive to EMI (even from HF). 

The 723-based screen regulator described on my Web site ...
http://www.vcnet.com/measures 
... works satisfactorily in the presence of RF.  I use it in my 8169 AB1 
amplifier.  The screen regulator is virtually RF-proof even though it is 
minimally shielded.  The trick was to add enough R to the 723'a 
non-inverting input pin to prevent RFI to the extraordinarily high I-gain 
error-amplifier and comparitor.  
......

>The refrigerator and air conditioner start at the same time, the 
>lights flicker, the filament drops to 4.65 volts for just a second, 
>and you now have to wait wait three minutes to talk.

This would not happen if the designer added a c. 2-sec. R/C delay to the 
sampler.  
....
>.......  This seems like a case of "do it my way, it's the only right 
>way".
>
It was the only way I found that the 723 could pass the Joel/N6AMG RFI 
test . More gain is not always better.  
- Rich - 

R. L. Measures, 805-386-3734, AG6K   


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