[Boatanchors] carbon comp resistors failure mode?

[GGLL]

	It could be a leaky coupling capacitor; if the negative supply stays 
steady (have you checked it?), that capacitor could be "leaking" some +B 
from the previous stage plate voltage, so the bias becomes less negative.

Regards
Guillermo - LU8EYW.

W2HX escribió:
> Hello all,
> 
>  
> 
> I am trying to troubleshoot some odd behavior in a bias supply/keying
> circuit of an amp.  I am trying to figure out why the bias supply slowly
> becomes less negative as the system warms up when it should not. This is
> causing the finals to begin conducting when they should be in cutoff even
> though the system isn't keyed!
> 
>  
> 
> It is quite a complicated little system, but I was thinking that one
> possible cause of this could be a bad resistor.  There is a 2W carbon
> composition resistor in such a place in the circuit as to be suspect. 
> 
>  
> 
> But the question is, is it a common failure mode for a carbon comp to LOWER
> in value as it warms up? Has anyone seen that behavior? Or should I bark up
> another tree?
> 
>  
> 
> Thanks
> 
> Eugene w2hx
> 
>  
> 
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