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New uBitx 6.1 - Have I already blown the finals?


Robert D. Bowers
 

When I adjusted in my Bitx20, I used a fuse rated low enough that when I did overdrive the finals (the adjustment was a bit tricky - I think backwards to what I expected or something like that), the fuse blew.  That saved the finals!

Bob


On 6/12/20 6:57 PM, Gordon Gibby wrote:
be sure to read the directions carefully---plenty of people have flat KILLED those finals by doing this move wrongly.

Gordon


On Fri, Jun 12, 2020 at 12:25 PM Evan Hand <elhandjr@...> wrote:
I have been using 13.8 volts to finals, and a forward diode drop to the mainboard.  Either will work, it is getting the gate voltage to the correct value for the linear region of the IRF510.

73
Evan
AC9TU


Gordon Gibby
 

be sure to read the directions carefully---plenty of people have flat KILLED those finals by doing this move wrongly.

Gordon


On Fri, Jun 12, 2020 at 12:25 PM Evan Hand <elhandjr@...> wrote:
I have been using 13.8 volts to finals, and a forward diode drop to the mainboard.  Either will work, it is getting the gate voltage to the correct value for the linear region of the IRF510.

73
Evan
AC9TU


Evan Hand
 

I have been using 13.8 volts to finals, and a forward diode drop to the mainboard.  Either will work, it is getting the gate voltage to the correct value for the linear region of the IRF510.

73
Evan
AC9TU


beakgeek@...
 

Hi Evan, thanks for the link, that's very helpful.

When setting the bias what voltage should I supply to the radio?  12V?  13.8V?

Thanks


Evan Hand
 

Before you pull the finals, run the bias adjustment calibration.  If you get the 200 ma change from receive to transmit without any audio (NOT CW), then most likely the finals are OK.  Here is the tuneup from HFSignals:
https://www.hfsignals.com/index.php/ubitx-tuneup/

If you cannot set up the bias, then the finals are most likely blown.

73
Evan
AC9TU


beakgeek@...
 

Thanks for the reply Stephen.  Adding a 4 pin mic socket and using a power mic is on my todo list, but definitely separate to the current problem.  I was seeing about 2 watts before and now I'm seeing just a twitch of the needle.  I have also tested with a CW tone and it's the same so not just a mic issue.

I will look for Reed's sketch to try out too.  I'm stuck with just listening for a while until I sort this problem out.


Stephen KO4CVU
 

Before you replace the transistors, connect a microphone with a preamplifier and put the Baofeng in a drawer. I had a similar problem with my uBITX v6.1 After a lot of heartache, I took Evan’s suggestion and bought a CB microphone with a built-in preamplifier. I finally made my first contact on the 10 meter band earlier this week with a station that was less than 7 miles away. He said my signal was weak, but he could hear me. Tonight, I made my first two contacts on the 40 meter band - one in Connecticut and one in Louisiana. I’m located in middle TN. There is a profound difference in the power output between the 10 meter and 40 meter band on the uBITX v6.1. My second suggestion is to load Reed’s latest sketch into the Arduino on your radio. It has made a world of difference in the user interface on my radio. Above all, don’t get discouraged. Take my word for it, the folks in this group are cheering you on and are ready to help you when you run into difficulties.


beakgeek@...
 

Hi,

Got a new uBitx 6.1  I only have 10m antennas currently so I hooked it up and I could see a couple of watts on the meter.  I know these radios have low power on 10.  Next day I tried to do a test on a local 10m net and I could only make the needle switch, it wasn't going up.

I suspect the finals have blown.  Is there anything I should check?  I ordered a couple of IRF510s off Amazon, should be here Saturday.  Should I just go ahead and swap both transistors?

A couple of other things... I keep finding weird tones on some frequencies which aren't there on some of my other radios.  And the audio is far too quiet on low signals, what can I do about that?

Thanks