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[Amps] SB-220 Still testing

To: amps@contesting.com
Subject: [Amps] SB-220 Still testing
From: Darryl Kwasny <djkwasny@yahoo.com>
Date: Tue, 16 Oct 2007 08:11:25 -0700 (PDT)
List-post: <mailto:amps@contesting.com>
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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