SB-200 Problem

[Carlos Avellanet]

Hi gang,

  Remember my SB-200 project a few months back?  Well, it is back.  After I fixed it with your help, of course, I put it away for a little while because I got my hand on another one in better shape.  Today I got it out of the closet to replace the face plate.  I decided to give it a try to see how it worked and sure enough, bang!  The 1 ohm 5 watt resistor R-12 blew out as soon as I turned power on.  I have been scratching my head all day trying to figure out what's wrong.  Double checked all connections and all diodes and caps in the circuit.  It all checks good. I installed another resistor and removed the tubes...everything's cool.  I reinstalled a spare set of tubes and the resistor blew out just the same in no time flat.

Different tubes, different resistor.   A background refresher...the amp was tripping the circuit breakers when I first got it.   I installed new caps, bleeder resistors and diodes in the power supply an couple of months back.  R-12 blew then but it never did it again after I replaced it.  I used the amp for a good two weeks before I put it in the closet, no problems. I never did get to change the face plate so I had not even opened the case when the resistor blew this time around.  Any ideas because I am lost... :-)

Please reply to the list so everyone gets a chance to read and input.
73,
Carlos. KF4RRN

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