Re: uBITX finals get hot very fast #ubitx #ubitx-help #v5

Clark Martin

What is the idle current into the PA with the mic PTT pressed (or the equivalent)?  It should be 400 mA max.  That’s measuring the power just into the PA section.  The radio as a whole should be 500mA max.

How much power out are you getting on CW?

Clark Martin

On Aug 3, 2019, at 7:50 AM, Rob French (KC4UPR) <robert@...> wrote:

I've got a new uBITX v5.  I've only been using it for CW so far (haven't gotten around to wiring up the mic yet), but I've noticed that, after calling CQ a half dozen times, the finals get way hot... too hot to hold my finger on for more than a second or so.  

As far as I can tell, my antenna is good to go... according to my antenna analyzer, < 2:1 SWR across 40 meters, which is where I'm using it currently.  I guess I could try doing the same thing into a dummy load to verify that it's not due to an SWR problem.  

Other than loading the KD8CEC firmware and making some firmware configuration settings, I have not deviated from the stock configuration--same finals, same heatsinks, no change to PA bias settings.  

I'm assuming this is not normal.  Any thoughts on resolution?  I'm using a metal case that doesn't quite let me mount the board close enough to back to bolt the finals to the back panel, but I've thought of making a hole in the back panel to accomodate bolting on a larger heatsink.  But I'm also thinking that there may be bigger underlying problem that I address, regardless of whether or not I add a bigger heatsink, fan, etc.

Things I'm thinking I should do:
- Recreate my CQ calling into a dummy load, see how hot they got (does anyone have any metrics for key-down time versus temperature?)
- Measure the current draw on transmit, and/or perform the PA bias calibration from the HF Signals web site
- Build one of those LED SWR meters to back-up my antenna analyzer
- Any other thoughts?

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