[Amps] SB-220 Still testing

[Darryl Kwasny]

Well, I'm slowing overcoming my problems with the SB-220. I ran both tubes for several hours yesterday. With the plates disconnected. I then removed one tube and connected the plate. Fired it up and got about 100ma without drive. Tried driving it and the plate current would just drop to 0. Checked all the mods from Rich and everything looked good. So I sat around and pondered it for a while. I figured no ground to grid. Looked again and was disappointed to see that there was indeed a 30 ohm grid resister. Pondered some more and then checked the grid to ground. Nothing! I checked right across the resister and nothing! That resister was new and not smoked. It was a bad resister right out of the box. I suppose the warranty from Rich is long gone. :-)
   
  Anyway, replaced the resister this morning, popped one tube in and gave it some drive, drove it a little harder and it responded will. Drove it to about 250 to 300 watts out then shut it down.
   
  Took the tube out and put the other one in the other socket. Turned the amp on and it took out that grid resister. I suspected that tube might be bad because of the small bang a few years ago.
   
  Would everyone agree that the tube is belly up?
   
  I am going to look around for new Chinese tubes. Is any one manufacture any better than the others, if so which one. I am going to contact a guy that gets Pentas, are they one of the preferred brands?
  If not, which ones?
   
  Thanks, Darryl - K5WAS

       
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