Hi, Erich,
OK, that explains your symptoms. Note that R11/R12 and R23/R24 are 0.22 Ohms each, so that their parallel combination is 0.11 Ohms. They provide a small amount of DC negative feedback, but their primary function is that of providing a means of measuring the currents through the driver and PA stages.
With a combined resistance of 0.11 ohms, the voltage across the resistors is 0.11V/A. This is fed to a non-inverting DC amplifier formed by A1-A, with a loop gain set at +11, giving an output of 1.21V/A.
Whilst you have the PA board out, you might want to make the recommended modification to the pre-amplifier, TR1. There are two 'vacant' pads in the emitter circuit labelled C2 and R5. Revision A4 adds C2, 100nF, and R5, 10 ohms to increase the AC gain of this stage. When you have made this modification, you will need to reset both the CW and SSB drive levels.
If I can be of any further help, let me know.
73, Adrian, 5B4AIY