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Fender Concert bias reading?


 
3/29/2003 4:49 AM
Patrick Smith
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Fender Concert bias reading?
hey guys, i have a buddies Fender Concert amp that had what ended up being a bad power tube. It's working fine now but just for kicks i put the bias probe on the power tubes....and i'm getting no reading....0.00, nuttin! I've never seen this on any of my Fenders, Marshalls, or Hiwatt....am i missing something? why would i be getting no reading? I mean the amp works just fine, but clocks in at 0 mA on pin 8 of each power tube....wierd  
 
any ideas? thanks in advance for any help or info  
 
PMS
 
4/1/2003 6:08 PM
Major Pain 8^/
Your supposed to be reading millivolt and then times that by 1 to millamp.  
Example 30mv x1 = 30ma
 
4/2/2003 6:08 AM
Jack Collins
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I just fixed a crate 50 watter that had no  
bias current as read from my homemade bias  
probe.  
 
Turned out to be the cathode resitors were  
open. Close inspection revealed burnt spots  
under the resistors. Replaced them and bias  
came back.  
 
Of course the amp made no sound before the  
fix. Unlike yours.  
 
I do not under stand how an amp can have  
0 bias current, make noise and not have  
tubes melting down.
 
4/10/2003 9:34 PM
Bob M.
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Screw the bias probe and fix the amp in the traditional manner. Bias probes are intended for people who have no understanding of the workings of their amps. I get guys bringing amps to me all the time saying, "But my bias probe says....  
 
Whose your daddy: $10 Bias Probe or $300 Fluke DMM ?  
 
Bob M.
 
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