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[AMPS] SB-220 Problems

To: <amps@contesting.com>
Subject: [AMPS] SB-220 Problems
From: measures@vc.net (Rich Measures)
Date: Wed, 30 Dec 1998 10:39:46 -0800

>>A 20w resistor in a circuit where the dissipation is typ. 0.13a^2 x 20 
>>ohms = 0.34w?
>
>
>I suggest you consult  the schematic to determine the location of RFC-2
>Rich. 

?  Thanks, Carl.  The max. diss. would be 0.8a^2 x 20-ohms = 12.8w, so a 
20Wer would be a good choice.  
>........
>>>73  Carl  KM1H
>>>Amplifier Repairs and 6M Conversions our Speciality
>>>National Radio 1963-69    Part of NCL-2000 Design Team, Service Mgr
>>>1965-69
>>>
>>The NCL-2000 circuit design:used a killer screen-supply.  
>
>Separate winding on the xfmr, common useage for the times. Also was per
>RCA recommendations including the surge and fuse resistors used.
>
Many screens got toasted. 

>>2.  did not protect the 8122's unusually delicate screen from 
>>excessive >screen current. 
>
>Screen trip ckt was in the prototypes. RCA really tucked it to National
>with the early 8122 mfg problems. 
>
>>3.  ran grid current (Class AB2 grid-driven) which made ssb-doodoo.   
>
>With ALC connected it was simple to limit grid current and give
>acceptable doo doo. There is only 1dB difference in IMD3 between AB1 and
>AB2 with the 8122.

?  [chortle]  Apparently not simple enuff for trogs in the land of the 
fruits and nuts.  There were plenty of 'em who ran several mA of grid 
current, and thereby made abundant daytime forty-meter feculence.  //    
How much grid current did the manual say was ok?  
>
>>
>>4.  ignored a distortion-lowering circuit recommendation from RCA's 
>>8122 tech info. sheet.  
>
>Not according to RCA, suggest you get reading glasses.
>
?  As I recall,  RCA recommends a rf-nfb R in an unbypassed cathode, like 
Eimac recommends for the 4cx600, like Svetlana recommends for the 
4cx1600.  The NCL-2000 did not.  .  
>
>>5.  as I recall, used no low-L screen capacitor/collet bypass to 
>>improve vhf stability.  
>
>That is on the prototypes also.
>
?  another design change by bean-counters?

>As I stated here and to you in the past, what was designed in Engr is not
>what got built after the Marketing VP screwed around. 

?  R, R, R

>One engr quit in
>disgust. I transfered to the Svc Dept, wrote NCL service bulletins and
>was soon promoted to Svc Mgr. over the objections of the idiot in
>Marketing. He left years before I did.
>
?  If I came with an amplifier design that was subsequently changed by 
schmucks, I would not want my name associated with their mistakes. 
-  cheers.  


Rich...

R. L. Measures, 805-386-3734, AG6K, www.vcnet.com/measures  


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