New to the list and need help. First I will list the problem(s) and list
what I have in the amp. This is my first and last homebrew project so I am
not an expert with the math.
1. main problem is a blue glow at the bottom of the tube ONLY when keyed,
drive or no drive.
2. 7.2 MHZ tune up the plate choke gets hot, burning wire
smell.....measures about 84-87 uh.
3. blue glow in tube on any band. when keyed.
Now here are the specs:
5000 vdc no load, 4300 vdc full load, 600ma, center tap full wave with 16
mf filter caps, 117k bleeder resistors.
Tube is cathode driven with a pi network on the input. The grid and screen
pins are to ground. There is a 7.5 v zener in the cathode metering circuits
and a relay that cuts the tube off when in idle mode, a 15k resistor is
across that. Plate idle current is about 200 mils, with 125 watts drive on
75 meters will give me about 650-700 mils on the plate---ZERO grid current,
and about 1350 watts out measured with a Bird Thruline meter. 150 watts of
drive, 1800 out. I have 0 grid all the time, is my bias meter circuit
wrong or what. I know this is not much info but I can figure out most
problems, but the blue glow has me baffled. Yes i have several tubes and
they all do the same, so its not a "bad tube". The input circuits have been
tuned for minimum swr on the bands 1.5 or less. Now the filament choke is
very close to the input coils, could I be picking up some AC field here??
The B- goes to meter circuit through a 12 ohm resistor, I get no reading on
the grid meter, I should have a little grid current.....Where go from
here. thanks Richard
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