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It should work right out of the box, once you have followed the wireup instructions from hfsigs.com.
If it doesn't, check all those coils for cold solder joints, broken wires, and shorts, as that seems to be
the primary source of trouble on these rigs.
Check out the receiver first, but will take a halfway decent antenna to get any signals since gain is
kept low to avoid overload when using a "real" antenna.
Avoid feeding the rig more than 12v, I'd recommend using a 1A fuse into the main rig,
and a 2A fuse into the IRF510. ?If you don't have an RF wattmeter,?
use a 2w 50ohm resistor as a dummy load,?it should get hot when transmitting?
while yelling into the mike. ?Better yet, build a diode RF?detector, and measure?
the RF voltage across the dummy load.
With the original firmware, the operating frequency may jump around a hundred hz or so,
enough that I wouldn't want to put it on the air.
So once you think the rig is working, next step is to figure out how to download Allard's code:
? ??
I suggest you just add the function button, and avoid the other mods till you know the rig is working well.

Here's a couple other mods to consider:
??/g/BITX20/message/33933

Some insist that everyone avoid any chance of the 2'd harmonic not meeting the letter of the law.
It's good to add that 100pf C0G/NP0/SiverMica cap to?the output low pass filter, rated for at least 100v.

The typical 100w ssb transmission may well have a 2'd harmonic that's 10db worse than our 5w bitx40.
FCC regs state that we should use "the minimum transmitter power necessary to carry out the desired communications".
Ignoring that directive (as many operators do) seems a far greater sin. ?

Q15 can be blown by several volts at the base if your bitx40 is hooked up to an antenna while a nearby rig
is dumping 100w into some other antenna. ?If that's in your future you should do the double-diode mod.?
?
Good luck!

Jerry, KE7ER