#v5 finally got my V5 together and working, PA bias question #ubitx #v5 #pabias

Dennis KL4LG

Got the radio up and running, I got a higher then 1 amp current draw when giving it the HELLO!!!  it's about 1.25 amps should I tweak the bias or let it ride?

Dennis KL4LG

my setup is as follows, i have a bench power supply set at 12v usually flicks up too 12.1, antenna is plugged into a dummy load
I am seeing the increased draw on my bench power supply. Is this over current going to damage my bitx, should I go through the tune up steps? Any one?


Hi Dennis,

This seems perfectly normal to me.  My v3 (as delivered without and changes to the bias) on CW drew from 2A on 80m to less than 1A on 10m, on SSB with a microphone and a loud "hello" it should require similar current draw.

Did you read somewhere that it is supposed just draw 1A?  This wouldn't made sense.  The rig draws about half and amp on idle without speaking into the mic.  So that figure would make just half an amp over that for transmission.  0.5A x 12V makes 6W consumption and at about 2/3 efficiency that makes just 4W out -- for sure the radio can do more than that on some bands.



Wayne Leake

 I think there is some confusion here.
 some are confusing the draw of the final or finals  with total draw of the whole unit in  TX  mode.
 Wayne WA2YNE


Dennis KL4LG

I had read somewhere that when adjusting the pa bias on the ubitx you did not want to draw more than one amp when measured between transceiver and the power supply.

I have been trying to measure base line voltage, current, and resistance readings, so if I smoke something I can troubleshoot easier.


Hi Dennis,

The manufacturer has a page for setting the PA bias; I would go by that recommendation for sure:

ubitx tuneup

The instructions call for 100mA above background current requirement for each PA transistor.  This is set by triggering the PTT with no mic input, then adjusting each PA transistor's bias pot.  In the end, with no voice input, your rig should consume about 0.7A

Once that is set, giving a loud "helloooooo" will increase consumption significantly, depending on the chosen band also.