Re: RD16HHF1 in the uBITX #ubitx

Jerry Gaffke
 

Curious.
Farhan recommends 100ma of bias through each uBitx FET, same as the Bitx40:
    http://www.hfsignals.com/index.php/ubitx-tuneup/
WA2EBY recommends 10ma in part2 of his writeup.

It does make sense on the Bitx40 to have a heavy quiescent current, since it is not push-pull.

You definitely want to zero the bias pots (RV2 and RV3 both clockwise on the uBitx)
before powering it up with new FET's, and then carefully adjust for the desired quiescent drain current.
Even if the new FET's are from the same lot as what was replaced, as the Vgs threshold 
can vary significantly from part to part.

Jerry, KE7ER




HFSingnals  bias current through each FET of 100ma can remain as it was on the uBitx.


On Mon, Feb 5, 2018 at 12:03 am, K9HZ wrote:
Nope. Close enough. 

  

On Feb 4, 2018, at 10:39 PM, Nick VK4PLN <nickpullen@...> wrote:

Excellent, thats what I am hoping to get to.
So the bias will need re-adjusting... Easy....?
What about the input and output transformers? I assume this will need modification due to the differnet impedances of the IRF and RD...

Thanks everyone for your input so far.
73.NIck VK4PLN

Join BITX20@groups.io to automatically receive all group messages.