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Basic Questions about Cathode Biasing

6/10/1998 11:59 AM
Xavier ChoBasic Questions about Cathode Biasing
It's been such a long time since my last post... I had to re-install my Win95 and other programs nearly 2 Gbytes total...  
 
...Anyway, I recovered my Netscape, and I'm here again... Thanks all who answered my post.  
 
...My custom-wound trans turned out to have no center-tap for fixed bias. So I decided to rebuild my Tweed (nearly the same as the one in Ampage Schems page - tweedpre & tweedpwr50) to have cathode bias instead.  
 
I tried 250 ohm/20W for the cathode resistor and 50 uF/50V for the bypass cap.  
 
But I couldn't get any sound with both 220 k grid-leak resistors grounded, and rather small and unpleasing sound when removed. And in the latter case, treble and bass control didn't make any audible difference in tonality and mid nob was acting just like gain - No sound at 0, and full gain at 10.  
 
I'm not sure whether it is a proper method for cathode biasing that just get rid of all parts concerning fixed bias (from diode to 220k grid-leak resistors) and put 250 ohm res. and 50 uF cap to the common cathode of 6L6's.  
 
And if there're other possibilities which cause above control problem, please let me know that...  
 
...  
 
Thanks.  
 
 
Xavier

 
Replies:
Jim S. What voltages do you measure at the... -- 6/10/1998 2:29 PM
Charles Hey... there's some good threads on... -- 6/10/1998 7:40 PM
Xavier Cho Wow... Incredible thing happened! ... -- 6/11/1998 8:56 AM