Tuning Procedure

[W3UTD]

Coming from ricebox transceivers ... now learning to tune my Ranger

"Dip the plate current" : I understand that

then the manual says "Increase the loading on the final by adjusting the Coupling controls".  What does "increase the loading" mean?  How do I know if I'm increasing or decreasing it?

[N2DTS]

Don't get Stu started!

When you increase the loading, you increase the plate current of the final and power output.
That is usually clockwise rotation.
Dip, load, redip, reload, etc, until you get to the correct plate current.

Brett

[WQ9E]

On the Ranger, loading is increased by turning both the coarse and fine coupling controls clockwise.  I don't have a manual nearby but I believe typical settings are listed in the manual and you can use these as a good starting point.

As you increase the loading the plate current will rise and you need to redip the final after every step of the coarse loading control and after every major change in the fine loading control.  Typically, with the fine coupling set to minimum (fully CCW) increase the coarse coupling control one step at a time and dip the final until you reach the point where the plate current is just a little below the desired amount.  Then use the fine coupling control to increase to the target plate current and dip one last time.

You will likely need to increase grid current back to the target value during this process IF you have to significantly increase coupling from the starting point.

If you load the final too heavily then the plate current will be higher than desired and it is likely the output power will actually drop.  So at the end of the process, you want to end up with the plate current at or slightly below the target value and the grid current at the target value.

Using the light bulb as a dummy load is a great way to actually see what happens as you adjust (and perhaps mis-adjust) the coupling control

[K1JJ]

The acid test to know which way to move the loading capacitor for heavier loading is to shine a flashight in there and tune the loading cap. When it unmeshes, (less C) this is loading the amplifier more heavily resulting in more plate current.

On my linear amps, I have an arrow marked to show the direction of less C. Loading a linear amplifer more heavily, past  peak power, is important for cleanliness.   However, for a class C amplifier, like yours, it is more of a power output adjustment and doubles to match the antenna to the final as part of the pi-network.

As Bruce said, just adjust and dip until you get the desired plate current or output power.

Hope this helps.



T

[W3UTD]

Thanks everyone!

[WA1GFZ]

Do not rotate the course control while transmitting. That could damage the switch contacts.

[K5UJ]

UTD this confused me also at first.  Remember you are tuning the tank circuit to match the plate to the load.  If you have experience tuning a ham amp like a gg cathode driven triode amp you know you mostly just tune for max power out and back off on the load cap a bit.  you think, what is all this dipping about? 

A high level plate modulated AM rig like a Ranger has a class C RF PA and all you are doing is tuning the carrier.  Remember the plate current meter only reads average plate current.   The 6146 is only conducting a small part of the RF cycle, just at the current peak.  You see a dip in average plate current when the tank is resonant because paradoxically, you are seeing the most current getting to the load (the antenna) at the dip because you are seeing the actual minimal average based only on the tube conducting and not flywheel current in the tank.

Linear amps biased in class AB or B have a dip but it is not as sharp and noticeable because the tubes are conducting for almost a half cycle so with them it is usually easier to tune with a watt meter on the output then increase the loading a touch by reducing the load cap value.

Rob