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previous: Enzo Perfectly normal. Keep an eye on i... -- 4/15/2003 7:10 AM View Thread

Re: Is it normal for bias to drift as an amp warms up??

4/15/2003 3:19 PM
JRRe: Is it normal for bias to drift as an amp warms up??
Thanks for the replys everyone. The amp is an Ampeg VL1002. I have another one of these heads which doesn't do this which is why I suspect something. None of my Marshall's or homebrews drift this much either. 20mA just seems excessive. What would be some obvious components to check? How bout the bias range resistor? Someone (I don't know if it was factory) soldered another resistor in parallel to the stock one. They both look like 1/2 watt though one may be 1/4.  
The problem was that I let it warm up for a few minutes then started playing and it sounded totally crappy - muddy and harsh. I checked the bias and it was only at 21mA so I increased it to 35mA and it sounded great. But then I watched it over the span of about 20 minutes and it kept going up!  
 
Anyway, your feedback is greatly appreciated!  
 
JR

 
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