[Amps] LK550 neg grid ... and bandswitch woes

[Gudguyham at aol.com]

In a message dated 11/25/2010 12:56:12 A.M. Eastern Standard Time,  
Gary at isect.com writes:

Any idea  what fault would cause my old and previously faithful Amp Supply 
Co
LK550  sometimes to register ~400mA of plate current and negative grid
current,  even with no PTT and no drive?  


A bad tube with an intermittent grid to filament short.  Usually when  the 
grid current goes negative but the amp works OK then your grid shunt  
resistor is open.  In your case I suspect a bad tube.  If you had said  you got 
plate current in idle no drive, I would say it is oscillating.  But  you got a 
questionable tube I think.