[Johnson] Johnson Invader 2000 problem

[Ray, W2EC]

George,

For some reason, the Invader 2000 needs periodic alignment of the driver
to maintain adequate grid current. Have you done an alignment of the
driver chain? I have done mine several times a year to maintain max drive.

However, the prime problem may be that the Invader 2000 seems to be very
sensitive to the 12BY7A driver used. When I first got it I had to swap
out a half dozen or so tubes to find one that would give me max grid
drive. An interesting point is that the tube that gave me the best drive
on all bands was NOT the tube that tested best on my tube tester. Do not
rely on a tube tester to find a tube with high gain. Actually swap tubes
and realign until you find one that performs the best.

"http://www.w2ec.com/invader.html"

73, Ray  W2EC



George wrote:

 > Hello all,
 >
 > Here's a chain of events leading to a problem that I could use some help
 > with.
 >
 > I bought an Invader 2000 a while back at a hamfest and immediately had
 > problems with the fuse in the low voltage supply blowing after about 5
 > minutes in the standby mode.  This only happened when the rig was set 
to use
 > the high power finals and the 4-400A filaments were on.  I tried 
everything
 > and drove myself nuts.  It turned out to be a bad 4-400A.  When the 
finals
 > were replaced with new Amperex 4-400As, the fuse no longer blows and 
I get a
 > final plate current reading on the meter (which I didn't get before).
 >
 > But now I have another problem.  The tune up procedure is to tune the
 > exciter ( 2-6146s) for max output as shown on the internal meter and then
 > adjust the 4-400A grid current to 10ma.  This is done with the 4-400A 
plate
 > voltage off.  Then turn the plate supply on and load up the finals.  The
 > problem is that with or without plate voltage, there is almost 0 grid
 > current showing on the meter and I can only load the finals to about 225
 > watts out on a bird meter.  Before replacing the finals, I could get grid
 > current showing but could not load the finals (I had to work fast 
before the
 > fuse blew).
 >
 > So my problem is, what could cause no grid current.  The exciter is 
putting
 > out full power.  When in low power mode, the bird shows about 120 
watts out
 > from the 6146s.
 >
 > Thanks for the help.
 >
 > George, NY2O
 >
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