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Re: Bassmen with 16R loads (loadline antics)


 :
10/15/1999 5:48 PM
R.G.
Re: Bassmen with 16R loads (loadline antics)
I'd be willing to bet that you've picked the right failure mode, Randall. Ken's right that the available current to the OT just can't go up much *with a properly operating tube* in place. The failure mode is probably that when the tube dies shorted, the OT dies.  
 
Here's another scenario - the load runs the tube into overheat, the tube shorts plate to cathode and the current goes skyrocketing - but not enough to take out the transformer by itself. The winding temperature on the half-primary involved shoots up, and then the tube burns the short open.  
 
Then you get a proper flyback spike! This time it's the inductance of the whole half primary loaded with more-than-max current, and any energy that can't be forced into the other tube or the load pops the insulation on a turn, or arcs the tube socket of the other tube.  
 
I think that the MOSFET current monitor circuit monitor might stop this. When the current first peaks, the MOSFET shuts down the B+ current through the output stage so you can't get to the hypothesized local heating and final flyback spike.
 

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