[Johnson] Ranger Problem # 3

[Gary Schafer]

Hi Wayne,

It sounds like you went too far down on the slider and dropped the 
screen voltage too much.

I have never had a ranger so I don't know exactly how everything works 
on cw but the clamp tube usually operates this way:
With no grid drive to the final (key open) there is no bias developed at 
the grid. Note that the clamp tube grid gets it's bias from the grid 
leak bias developed by the final when it is driven.

With no bias on the clamp tube it draws heavy current. Its plate is 
connected to the finals screen. The final screen gets its voltage 
through a dropping resistor. As the clamp draws heavy current that drops 
  the final's screen voltage to a low value and just about cuts the 
final off. The plate current on the final will be very low.

As drive is applied to the grid of the final it draws current. Bias 
voltage is developed across the grid resistor. The clamp tube's grid is 
also connected to the same resistor. That puts bias on the clamp tube 
grid and decreases its conduction. As the clamp tube conducts less it 
doesn't pull the finals screen voltage down as far and the screen 
voltage goes up to where it should be, allowing the final to draw screen 
current and thus plate current.

If your drive is low (not developing enough bias) the clamp tube will 
not fully cut off and will not allow the final screen voltage to rise 
high enough.

If the SCREEN VOLTAGE ON THE CLAMP TUBE is set too high its gain will be 
higher than normal and the bias applied to its grid will not be enough 
to cut it off completely. That will not allow full screen voltage on the 
final. That is what was happening before.

If the SCREEN VOLTAGE ON THE CLAMP TUBE is set too low its gain will be 
too low and it will not conduct hard enough to pull the finals screen 
voltage down low enough to cut the final off when there is no drive (key 
open).
This sounds like what is happening to your rig.

Did you set the modulator screen voltage per the manual? since the clamp 
tube screen is tied to the modulator screens the voltage is going to be 
common. You should set that slider resistor to the value they suggest in 
the manual. I am guessing that they will tell you how much the modulator 
screen voltage should be in a particular mode. AM or CW.

If you set the screen voltage to the proper level and there is still a 
problem, try a different clamp tube as Glen suggested.

73
Gary  K4FMX


Wayne Light wrote:
> Glen and Gary...you guys were right on the money.  I moved the "slider" down on R-35 and that dropped  the screen voltage... and "viola" I had full plate current (with the damper tube in) and tunes fine. Thank you. I am sure impressed how you can accurately trouble shoot this over email!
>  
> Now one last bit of advice please. As I was checking the Ranger out., I put it in the CW mode, the plate current pegged (with the key open). I was monitoring the output and there was no output. When I closed the key, the plate current went to where I had previously dipped it for the phone tune up and a nice CW was sent.  In other words, the meter is reading backwards. When keying it, the plate current goes down to the correct MA.  Maybe I should reverse the wires on the key (NO...I'm not quite that bad... yet). :)  I'm sure it is not "cool" to have the meter pegged at 150 MA (except when it is transmitting).
>  
> Any ideas?
>  
> Thanks again. I really appreciate the help in getting this unit on the air.
>  
> Wayne
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