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Hello.

I just finished building my Bitx40 v3 board using a amateurradiokits.in case and a Baofeng mic modified as per?



The receive seems to work well.? I hooked the radio up to a receive loop antennas and was able to hear some local stations called CQ for a contest.? I then plugged the Bitx40 into a dummy load and put an ammeter in line with the power connection to do the alignment.? This is where things went a bit wrong.??

According to the Alignment of the Bix 40 section of this page



I should adjust RV1 fully clockwise so the ammeter reads 0, however when I turn the radio on the ammeter immediately reads 150mA, no matter how I adjust RV1.? If I key down current jumps from 150mA to some other value depending on how RV1 is adjusted (between 280mA and 1A).? I also noticed that when I do the HAALOOOWW into the Mic current doesn't change at all even though I've keyed down (setting RV1 doesn't seem to change this at all).? I've also fiddled with RV136 which made no difference.

My PTT seems to be working, however I'm suspicious of the Mic.? I did check continuity from the pads of the electret all the way to the board and it is good.? The PTT and electret do share a common ground as per the instructions I linked above.

So basically two problems.
Receive current should be close to zero according to alignment instructions, but it's 150mA.? Also I push the PTT and current jumps a bit, but doesn't jump when I speak into the Mic.

Any thoughts?
Craig (VE6TBW).

The alignment current refers to only the current in the PA power line, not the entire radio. On that line current is zero during receive, but the overall rig does draw power on receive and you would have to add 100ma to the receive current when you key the radio without modulation.

The lack of further increase suggests something is wrong, either the mic is not connected properly or you may have a blown Q13, which is common if you haven't made the back-to-back diode mod and have a higher power transmitter nearby, even if the BitX40 is not connected to anything.

=Vic=

Hello.

It looks like I've damaged Q13 on my Bitx40 v3 board, this is annoying because the diodes for the protection modification are sitting on my bench not installed.? I happen to have some 2N3904 through hole parts sitting here.? Is there a good quality way to substitute that in, or should I order a new SMT version of that transistor?? I looked around and say lots of people who said they need to replace it, but none mentioned how.

I suspect I blew Q13 because I used a W6LVP receive loop on the radio and it has a preamp on it.

Should be easy enough to replace Q13 with a through-hole 2n3904.
And should work fine.

You need to first remove the old surface mount MMBT3904 at Q13.
Heat up the pin that's alone along one side with a soldering iron and lift that pin off the board a little bit with a knife.
Then do the same with the other two pins.

Solder the leads of your new 2n3904 to the appropriate ends of R132 and R134.

Jerry



I suggest you first remove the old su

Hiho!

Am 08.10.18 um 21:56 schrieb craigmclean@...:
[...]

I should adjust RV1 fully clockwise so the ammeter reads 0, however when I turn the radio on the ammeter immediately reads 150mA, no matter how I

Don't mix em up with checking the PA current <-> main current. Only measuere the PA part. Maybe this was the problem here?

adjust RV1.? If I key down current jumps from 150mA to some other value depending on how RV1 is adjusted (between 280mA and 1A).? I also noticed that when I do the HAALOOOWW into the Mic current doesn't change at all even though I've keyed down (setting RV1 doesn't seem to change this at all).? I've also fiddled with RV136 which made no difference.

[...]

Check out R123, too.

I am working with Alalrds v2 mod and compared the PA current with CW and Mic on LSB. Even I was shouting out loud in the mic I saw there no realy increase of the current.

So check out the same circuit part of the uBitx. There the resistor is called R63 and only has 47 Ohm.

Atm I soldered in a 10 Ohm (may be to low) and will check out the outgoing modulation/signal asap. But now the consumption of the PA current is equal or higher than in CW.

Btw: meanwhile I had added simple mic gain circuit (thx to dl2qa) but I like the simple solution with replacing R123 much more now.


--
Liebe Gruesse, with best regards,
Stephan Lauffer

DC8LZ, QTH JN37XX

Hello

It appears that asking a question on the Internet is the best way to embarrass yourself.

I replaced Q13 with a through hole 2N3904 and that did not resolve the problem.? I then took the build from the top and rechecked everything and realized I'd connected the electret microphone backwards.? I fixed that problem and still current wouldn't jump when I talked.? I figured I may have damaged the mic by connecting it backwards so I replaced it with another one I have here, that did the trick. After fixing the Mic connection and connecting the ammeter at the PA Power, not at my external power supply things starting behaving a lot better (thank you to Vic for pointing that out).

I do have a new question though.

I've adjusted PA Bias using RV1 to 100mA and when I say HAALLOOOWW into the mic current jumps up to 500mA or so.? I've adjust PA Drive using RV136 all the way up and I still only get to about 800mA.? Is that normal.? The alignment instructions suggest it should get to 1A.? I've even tried shouting into the mic and it never gets much beyond 800mA.? Would Stephan's suggestion work to get it closer to 1A?? I'm still using stock firmware.

Any thought's and thank you to those who responded so far.

Craig (VE6TBW)

One other question.

If I have replaced Q13 with a larger through hole version of the transistor, is the diode protection mod still required to protect that transistor?

The through-hole 2n3904 uses a silicon die that is identical to the surfacemount MMBT3904.
The through hole package can dissipate more power,
but I believe the failure mode is excessive voltage punching through a junction.

So yes, still need diode protection.

When I replaced Q13 after blowing it I used a 2N2222A as I had several on hand. I found the stage gain was significantly less and I had to increase the drive? to get the same power with modulation as I has seen before, so I suspect something like that may be true with the 2N3904 you used. Also, the output of various electret elements seems to vary a little and I've read that some add a mic preamp stage to accommodate the mic they used. Glad you got it figured out, though.

=Vic=