Ranger won't load properly. Plate current won't go below 135/140 millls?

[N2IDU]

I am unable to dip the final plate current below 135/140 mills on 160 and 80 meters on my Ranger. It will only get down to this value in the 1st and 2nd position on the loading switch and with about 3 1/2 mills of grid current. At 2 mills of grid current, plate current will only dip to about 175 or 180 mills.  Any loading position higher than 1 & 2  puts the plate current way to high. The other bands 40 meter and higher, are not affected by this malady. I am operating the Ranger into a 50 0hm non inductive dummy load using a thruline bird watt meter.

I have checked or replaced the following to no avail:

Tried several 6146's both new and old. Same loading results as above. 
All the 300 pf and 150 pf series mica caps used in the loading circuit switch. All check perfect.
I checked the 20 ohm shunt resistor used in the circuit to measure the grid current for the meter. It checked out perfectly.
Tried different 50 ohm  dummy loads.

Any suggestions will be very appreciated.

Sincerely,

N2IDU "Old Shincracker Vt" 

[WQ9E]

Hi,

On 160 and 80 the Ranger will generally require coarse loading at minimum and fine loading near minimum.  Is your fine coupling control truly at minimum (perhaps the knob is not indexed properly).

Did you also check the shunt resistor for the plate position to make sure it is OK (or place a known good meter with sufficient HV insulation in the plate supply to the cold end of the plate supply RF choke to check actual current draw).

Any chance something is going on with the buffer tuning?  Although class C amps need their proper drive, I am surprised to see the plate current drop at resonance when you increased grid drive by 50%.  If you have a scope, it would be nice to see what is coming out of the multiplier stage on 80/160 in case you have some spur in that stage.

This is a problem I have never had with my Ranger or Ranger II; hum is my specialty since my Ranger 1 has had 4 separate "hum events" in the 3 years that I have owned it.  I do have to keep mine loaded to minimum since I use it as an RF and AF driver for my Desk KW.  I am adding an outboard attenuator to better match its output capabilities with the needs of the Desk KW.

Rodger WQ9E

[Pete, WA2CWA]

I would just check all parts of the band switch wafers including the mechanical linkage towards the front. I would suspect this since it appears to be happening only on 160 and 80 meters. Grid current normally should be between 2.5 and 3 ma. I run mine at 3 ma.

[The Slab Bacon]

Rangers use grid leak biass on the final, and screen clamp tube (6AQ5) to protect the final. I have found that the plate current will decrease and the efficiency increase as you increase the grid drive to the final. Check the clamp tube, and the resistors associated with it to make sure they are ok as well. As the grid decreases the clamp tube should start to clamp down the screen voltage, if its not look hard at the clamper circuit.

                                       The Slab Bacon

[WU2D]

I agree that there is something wrong but try this: As an experiment, put another 150 pF or so from the output side of the final PI tank to ground. This will temporarily put more loading C on the output. If the meter comes down further, that could be a hint that it wants more loading.

Mike WU2D

[N2IDU]

Thanks for all the suggestions and tips.  I will attempt to work on the Ranger in the next week or so and report back with the results.

Sincerely,

Peter N2IDU
"Old Shincracker, VT."

[WD8BIL]

Peter.... look at a frequency counter and make sure the output is correct.
Ya might be tuning a harmonic which would indicate a buffer problem or output tamk switch problem.

[AB2EZ]

Peter

Following up on "Bacons" comments...

The problem may be that you have too much voltage on the screen of the 6146. As Bacon pointed out, if you reduce the grid current, the clamp tube will begin to draw current. The clamp tube draws current through the voltage-dropping resistor (R15, 30k ohms) that goes between the plate and the screen. This causes the screen voltage to drop... which would bring it back closer to the proper level... although this is obviously not the way you want to adjust the screen voltage.

Check to see if the resistor, R15 (a high wattage resistor, but also one that is dissipating a lot of power when the Ranger is on, particularly in "standby"), has changed value to a lower resistance than 30k ohms. If so, consider replacing it, or adding a suitable resistor in series to make up for the change.

If the value of R15 is close to 30k ohms (or a little higher)... then reducing the loading on the 6146 seems like a next thing to look at. This would require you to reduce the amount of loading capacitance (you already seem to be at the bottom of the range... which implies that the loading capacitor is already set to its minimum value), or to reduce the "Q" of the tank circuit... which would mean reducing (not too much) the amount of tank coil inductance that is being used on each of these bands.

Best regards
Stu