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Re: Shorted primary?

10/30/2004 12:05 AM
Enzo
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Re: Shorted primary?
When I see a tube amp blowing fuses I always suspect the power tubes first. If I pull them and it still blows fuses I look for shorted rectifiers, shorted flyback diodes off the output tube plates, and output tranny shorts.  
 
SHorted filters could cause this, but that doesn't seem to happen all that much. Also, if it is not the first or second filter, it won't blow fuses anyway. Once the B+ goes through a 10k resistor to get to the preamp supply, shorting said supply only puts a 10k resistor across B+, and that won't blow fuses.  
 
If there is no short to ground on the B+, then check those things. Disconnect the CT of the OT. If the fuse now holds, it is tranny or flybacks.  
 
You can check rectifier diodes in seconds, so why not start with that.  
 
Of course there are other odd things it could be - a little mylar cap shorted somewhere say.  
 
And don't forget the 6VAC lines. A bad pilot lamp socket can kill you. If it is coming loose and the two terminals rotate and touch, there is a dead short across the 6V winding and that will surely blow fuses. Might as well look into the bias supply too.

 
Replies:
Mark Lavelle [QUOTE]You can check rectifier diod... -- 11/6/2004 4:24 PM