Richard,
See below;
*********** REPLY SEPARATOR ***********
On 8/26/05 at 7:54 AM Richard Sisson wrote:
>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.
Probably nothing wrong as some glass will show that glow. If the glow is seen
in the innards of the tube, it's a gassy tube. If the glow is in the glass,
it's not bad.
>2. 7.2 MHZ tune up the plate choke gets hot, burning wire
>smell.....measures about 84-87 uh.
Sounds like a self resonance, or the choke doesn't have enough inductance at
the frequency its at, or the choke isn't big enough for the current through it.
If this happens on all bands, I'd say the wire isn't big enough for the current.
>3. blue glow in tube on any band. when keyed.
I doubt it's bad especially if the power out is correct.
>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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