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Hi everyone,

I applied some mods to my ??BitX v4 tonight.?? In general they seem to have worked, but I also seem to have lost the ability to transmit using SSB (CW seems to work beautifully).?? I was wondering if anyone could help me debug.

More details follow on the mods I applied and the specifics of the problem I'm now encountering.


=== What I did ===

I applied to following mods, in the order listed, testing CW into a power meter? + dummy load after each step:

1. Replaced the four relays near the antenna with the exact model of Axicom relays suggested ().

This resulted in slightly higher power output (10-20%) on 160m through 20m, and less or no increase in power on 17m-10m.

2. Replaced Q90 and R81 ( )

This increased power a bit on some bands (especially lower ones) and decreased it a bit on other (especially higher ones)

3. Replaced C81 (per above) and L5 & L7 ().

Resulted in increased measured power on all bands, except no effect on 30m

4. Replaced the 6 2N3904s with TO18 2N2222As (checking specs for both to ensure proper orientation) and doubled up the 4 adjacent resistors (per Allison's fix above)

Resulted in much higher measured power, nearly twice previous measurements on some bands, especially 10m, 17m, and 40m.?? Max I measured is ~26W at 1900kHz and minimum I measured is ~4.3W at 21MHz (although 21.2MHz was at ~9.3W).

I measured power at a list of 29 frequencies each time, and can send numbers and/or a graph if anyone's interested.?? I can also send pictures of the board.?? (Despite it basically being my first time soldering SMD, I think I did a decent job with all of it.?? And my solder removal skills definitely got some practice!)

Unfortunately I can't currently measure spurs or harmonics, but the hope is that these fixes reproduce others' results.


=== Afterwards ===

After I tested power output with CW, I hopped around 80m, 40m, and 20m, listening to FT8 and WSPR, and tried transmitting in both modes on 40m.?? After my WSPR transmit didn't seem to be picked up by anyone, I put my power meter inline again and found that SSB doesn't result in any power out (the relay clicks and the LED wired to the relay lights up, but there's no RF), with either my computer hooked up (using e.g. WSJT-X's "tune" button) or a microphone (+whistle test).?? The CW key still results in the power levels I measured after all the fixes.

I also noted that there is a new smoky smell coming from the board....?? Upon further inspection I noticed that some of the 2N2222As were a bit warm, but nothing else seemed out of the ordinary.


=== What I've checked ===

Besides a visual inspection that didn't yield much, I checked the line from the microphone itself to C60, and it does indeed conduct.?? Which leads me to believe that the problem is something on the board.

Note that I'm running the ??BitX on a 3A 13.8V power supply.?? I have a 3A fuse between power in and the on switch, which has never blown—but 2.5A fuses used to blow any time I had a little too much reflected power on some of the hotter (per original power measurements) bands (not as much of a problem with my current antenna on most bands).

I don't have much test equipment—mostly just a simple multimeter.??? I might be able to get access to an oscilloscope if really needed.

Any suggestions for things to check are welcome!


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Jonathan, KD5CFX