The Soldersmoke DC receiver project has been great fun but also quite frustrating. I got it working nicely if I used an external amplifier but the described three transistor high gain audio chain gave hardly any volume into my speaker. This has out-foxed me for far too long. I'm using 2N3904s with no particular manufacturer marking on them so had determined the leads using my fancy new FNIRSi component tester.
It's a bit hard to read in the photo but facing the flat side, the tester says the leads are C B E. The audio chain was working and had gain but I never got enough volume in the speaker. Nate, KA1MUQ, questioned the orientation of the transistors. I turned one around and there was lots more gain! Testing again, with my old clunker component tester gives the correct pinout.
Again, facing the flat site, but now the pins go E B C. Surprisingly different gain too hFE=170 compared to hFE of 215.
I was able to listen comfortably to sideband contacts with the amplifier driving a speaker directly.
Now my problem is "heartache of oscillation" (contrasting the "joy of oscillation" when building the VFO). The audio chain is very keen to take off at hundreds of kHz.
I found that even having the volume control off the board was enough to create instability. I've put it right back on the board and now all is working well.
Lessons learned: Component testers might not be right and transistors will work to some extent if wired with C and E swapped.
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