[Collins] re: newbie question (long)

[Dr. Gerald N. Johnson]

On Wed, 2008-06-18 at 12:58 -0700, wli wrote:
> Big thanks to all who replied to me!
> Your suggestions were most valuable to get me thinking....
> I got the unit working now (whew)
> 
> Here is what I did:
> L123 was electrically isolated for testing
> DC resistance 80 ohms, and no shorts to case
> 
> Found three "mods" that I missed initially  (DUMB ME!)
> 1) 22uF electrolytic across C215 correct polarity
> 2) 22uF electrolytic between neg post C216 and ground
>    negative pole was GROUNDED

That reverse biased electrolytic would hold the magnitude of the
negative voltage down. The lowered bias voltage would let all the stages
depending on it (like the audio output tube) draw excess current while
it raised the positive voltage at the rectifier cathode.

> 3) 10uF across C-223 correct polarity
> 
> Carefully looked at all solder joints: OK
> Checked all the oil filled caps: OK
> Pulled all the tubes, except for the 5V4 and OA2
> Monitored current draw off L123 and B+ at L123
> Added each tube one at a time working backwards, noting the current draw
> 
> Now B+ is 210VDC and total current draw is now just 54mA 
> 
> Now I can do the normal stuff like checking PTO tracking, etc etc
> 
> I did install a computer grade line filter with its 3 line socket
> The hot AC goes to the fuse/pwr switch
> The neutral goes to the pwr transformer
> The ground was resoldered to the chassis
> 
> W. Li
> 

-- 
73, Jerry, K0CQ, Technical Advisor to the CRA
All content copyright Dr. Gerald N. Johnson, electrical engineer