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SB200 Help Needed

E

edfiero

Active Member
Jul 15, 2010
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I have picked up an SB200.
I changed out the Caps on the power supply board and changed the RF input connector over to a normal Coax connector, and installed the Softkey.

When I got the amp, the power supply board was dark (burned) in the area of the 30k resistors. It seems that changing the caps didn't help this problem.
The amp will start smoking from the power supply area after being on for 3 or 4 minutes. Those resistors are extremely hot.

Another issue (or maybe related) is that the instructions indicate Plate Current, without exciter, should be 90ma. However mine is showing nothing.

What should I be checking?
 

edfiero said:
Thanks for this most helpful reply. Sign yourself up to be an Elmer to new hams.
Click to expand...
Its a truthful and factual statement. Truth hurts. You clearly have no understanding or experience with electronics. Add that to sticking your hands in a high voltage tube amplifier and messing around, the outcome is bleak. Have someone repair it, your nowhere near experienced enough.
 
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KneeBiter said:
Did you check all the diodes? Make sure none are shorted. Remove the tubes ?
Click to expand...
Thanks. Yes. I should have mentioned previously. I did check all the diodes in the power supply. All tested good. As well as those 30k resistors.

I have tested again with the tubes removed, and I'm still seeing smoke
 
I would disconnect the plate high-voltage at the board, or
disconnect meter circuit resistor R12. (this resistor usually
blows up during a tube failure on these types of amps)
a high-voltage probe would be nice to use here to measure.

Then "smoke test"

also, carefully, and quickly, at the tube sockets,
I would check for the filament voltage, and the negative
cut off bias at the grids. make sure all parts of the transformer
are good. I have had the smoke coming from a transformer
on various amps.
 
Be VERY Careful. There is some SERIOUS High Voltage in that amplifier that will KILL YOU Grave Yard DEAD & Fast. If you don't know what you are doing then leave it to a Professional since they get paid to save lives.
 
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