SB200 blowing fuses

[Karl France]

I contacted a buddy of mine who is an electronic design engineer (retired)  
and this is his recommendations ....hope this helps
 
Karl
W5QJE
 
 
OK, trouble shooting recommendations:
 
1.  Pull the tubes out------ power up and see what happens.
     Sounds like a High Voltage problem there.  If  the 2400
      VDC is there, no malfunctions, then the HV  power 
      supply is OK probably.  
 
2.   Check to see that you have the Neg 120 vdc on the 
      tube grid connection of the tubes.   When not keyed, 
      it should have the neg 120 vdc there.  
 
3.   Check the 6.3vdc filliment voltage AC VOLTAGE.  If it  is
      there, then it is probable that your  ceramic capacitors 
      are OK.  30+ year old TV type ceramic  caps look bad
       anyway, but are usually  OK.   
 
4.    Plug in ONE tube at a time.  One tube in,  one out. Try 
       operating the linear amplifier 250  watts output max.  If
       OK, then put in the second tube and  try again.
MAKE SURE-----YOU DO NOT OVER DRIVE THE AMPLIFIER.  IF YOU GO OVER 550  WATTS 
OUTPUT, THEN YOU CAN REACH THE LIMITS OF THE TWO 8 AMP CIRCUIT  
BREAKERS--------ESPECIALLY KEY DOWN SITUATIONS.  
 
These amplifiers will put out 700 watts, but not for long.  Keep the  output 
power down to 550 watts or less.  Detune using the LOAD variable  capacitor on 
the linear amplifier, this will reduce RF drive from the  transceiver.  OR 
reduce transceiver RF drive to control the output  power.  ALWAYS tune up with 
about 50 watts drive, before you run the power  up to full output.  
 
THOSE 8 amp circuit breakers are there to protect the high voltage power  
supply and TUBES.   When you push the amplifer OVER 500 watts output,  then you 
are overloading the HV power supply.  HEATHKIT specified the  amplifier at 1000 
WATTS (1 KW) INPUT POWER, because that is the  way the FCC specified the 
power limit back in the 1960's when this amplifier was  approved.  It does take 
about 120 watts to drive the amplifier to full  output on 10 meters only. 
Watch the on-board SWR/PWR meter-----limit power output to 500 watts and  you 
should be OK
 
                                CARL K8IHQ


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