Hello to the group!
I am working on an older homebrew amp with a tetrode.
The most obvious problem is that on 10M 15M and somewhat on 20M, the
output is
slow to develop. For instance, driving with 30 watts, the output of the
amp starts out
at about 400 watts and then about 3 seconds later , it will go to full
output (1500).
The grid current is normal on 160, 80, and 40. As you begin to
approach escessive
drive, the grid current rises to 20 or 30 microamps. The grid current
meter measures from 0 to 100 ua.
On the higher bands, as you start overdriving, the grid meter
deflects down (below
0 ). Obviously I cannot read the current. WHen the amp goes back to a
standby condition, the meter stays below 0 for a second or 2 and then
comes back to 0 .
Screen current does not flow until the tube output increases -
voltage is steady.
Grid voltage does not change.
I have tried several configurations of input circuits and they all
act the same.
Things that have been replaced or substituted.
tube socket
tube
input circuit (but not the 50 ohm load resistor)
cathode circuit components
I am somewhat suspicious of the tank circuit but unable to verify.
I think fixing the grid current issue will help get to the root of
the problem.
Any ideas?
Lynn, NO9Z
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