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Ampeg V-4 bias mod

7/21/2000 2:02 AM
Tom L
Ampeg V-4 bias mod
I added a bias pot to my V-4 per Ray Ivers's suggestion: a 68K resistor in series with a 50K  
variable-resistance-wired pot paralleled by a 47K resistor (thanks, Ray!). I then installed the power tubes and monitored the voltage drop across each of the plate resistors. I noticed two things: 1) the hottest setting of the bias pot gave me only about 25 ma plate current at idle; 2) plate voltage at idle was not steady--it would increase slightly at irregular intervals.  
 
I guess I'll substitute a smaller value resistor in the bias pot assembly at some point, but it sounds fine for now.  
 
Are the plate voltage fluctuations normal, or do they indicate a problem somewhere? If so, any ideas about what it might be?  
 
Thanks,  
 
--Tom

 
Replies:
Graywater Tom,I've got a V-4 ... -- 7/21/2000 11:56 AM