|Updated schematic (an error spotted by G3TFX)|
Click on the schematic for a larger, more readable, version. Please let me know if you spot any obvious errors (e.g. where I have put grossly wrong values of components in) so I can update the schematic.
Please feel free to use this as a starting point for your own version. All in, I doubt the components would cost more than £5 (7 euros or 8 dollars) even if all the parts were obtained new.
The 2N3866 runs quite hot in class A and I want to change this biasing in the final version. I may also susbstitute the 2N3866 for a couple of paralleled 2N3904s to save further cost.
The same circuit will work well on PSK31 (pull the crystal to the right frequency of course) but both with WSPR and PSK31 do not over drive the PA. This is a DSB transmitter and there will be splatter either side of the carrier for tens of kHz if driven too hard. Adjust the drive so the output from the PA is a clean, DSB signal free from obvious audio distortion.