Tube Amps / Music Electronics
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|10/15/1999 5:48 PM|
||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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