I have made further progress toward completion of my BITX20 Version 3. Today I completed the mounting of the boards within a case. The linear amplifier board is soldered to the back panel of the case and the main BITX20 V3 board is mounted upside down to the lid of the case. I have made a prototype front panel using plywood.
After this I was able to transmit on either of my antennas without the self oscillation problem I had earlier. However my output has greatly decreased and now I am only getting 500 mW out at full whistle. I have previously got 4 watts output.
I made a small modification and shifted the 0.1uF capacitor between the VFO oscillator Q6 and Q7 mounted it to a switch on the back panel. This switch allows me to use an external VFO rather than the internal VFO. Mounting the capacitor to the switch means the wires to and from the switch can connect in the holes where the capacitor was.