Hello,
I hope that some of the more experienced can give me some advice. I
am working on conversion of an older homebrew 4cx1500b to a gu84b.
The best description of the problem is that the higher the frequency,
the less the output. 160, 80, and 40M due pretty well. On 20 and above
loss of power output is
very high. Another interesting occurrence: With about 20 watts drive
on 20M,
output is about 30 watts. 2 - 4 seconds, the tube begins to amplify and
power out
goes to 400 or so (during this, input swr changes a lot - 1.3 to 2.5 to
1).
I have a mov tied to the grid input pin and screen input pin at the
socket. Is there too much capactiance from these devices? The tube is
grid fed via a .16uh inductor tied
to a 50 ohm 100 watt resistor to ground.
Plate voltage under load 2000
grid voltage under load -60
screen voltage under load 325 +
cathode tied to ground
tank circuit tuned to 2600 ohms
drive 30 watts
also, I have too much tune capacitance on 20M..... I cant set vacuum
variable in the tank circuit low enough...
ideas please.
Lynn, NO9Z
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