[Johnson] Johnson Invader 2000 problem

[George]

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