[Phil G4SPZ]

I can’t offer many suggestions David, other to say that when I built both my MiniMod AM modulators the RF waveform was a visibly purer sine wave. On yours, there’s some asymmetry, plus that little ‘kink’ on the negative-going half-cycle. Perhaps that’s the point on the transistor’s characteristic where it turns ‘on’ or ‘off’ or starts to saturate? I’ve not seen anything like that before.

What it will mean, of course, is that with no filtering the output will contain more harmonic energy than you might wish for. That vaguely sawtooth-like waveform means there will be both even and odd harmonics, which could extend well up into the spectrum. Have you tried listening on the second, third and higher harmonic frequencies? They should be well down on the fundamental. If they’re only weak you should be OK, but if they’re strong you might think about adding a simple low-pass filter. It might be easier to try adjusting the bias on the transistor whilst monitoring the waveform, to see if you can improve it.