[Amps] LK500-ZB

[Paul Decker]

Thanks to all that replied.   At this point, I think a tube has gone bad.  Removing the "bright" tube, the amp can be loaded up and produces output.   Swapping the sockets, the problem seems to follow the tube.   



As was pointed out, I don't have anything to loose with the bad tube.   There was some talk about "blowing the short out".   I don't have a 400VDC supply, but I guess I could rectify a 240 VAC line, that would get me about 380 VDC @ 15 amps.    Another suggested a car battery.   I do have an adjustable 60 vdc @ 60 A current limiting supply available.   Would I just put this to the heater pins? 



thanks, 

Paul (KG7HF) 







...when the amp is turned on, but in standby, the plate current reads about 200mA and the grid current is pegged negative.  Plate voltage is lower than what it used to be, about 2600 V.   Switching between RX/TX doesn't seem to have any affect, I can hear the relay kick.   One final observation, in RX, one tube starts to glow orange, while the other stays the normal light yellow color.  



It seems as if maybe somehow the tube is internally shorted or something.   Ideas, suggestions..