SB-200 Problem

[Mark Graalman WB8JKR]

  The only thing that's going to cause that is a HV short to ground, if
the tubes aren't bad I would look for a leaky bypass cap at the base of
the
plate choke, but I would suspect the electrolytics in the power supply
before
anything else especially if they are original. I would also place back to
back
connected silicon diodes across the meter movement to protect it in the
case of these problems, I'm surprised you haven't lost the meter movement
yet.

73,  Mark  WB8JKR


On Sat, 24 May 2003 20:16:27 -0500 Carlos Avellanet <avellanet at COX.NET>
writes:
> 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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