so ive been building this little 40m CW rig from scratch for the past few months, nothing fancy just a VFO driving a buffer and then a pair of 2N3553s in a push-pull final stage. got it all breadboarded and then transferred to a proper chassis last week. key clicks are clean, sidetone sounds good, but when i scope the output before the LPF it looks a bit ragged on the peaks. not terrible but not the clean sine i was expecting either.

the final is running maybe 3-4 watts into a dummy load, SWR is fine, but that waveform just bugs me. i checked the bias on the transistors and it seems okay, maybe a little warm but nothing crazy. could this be a keying waveform issue bleeding through or am i just looking at some harmonic content that the LPF will sort out anyway? i keep second guessing myself because this is my first real homebrew transmitter and i dont have a spectrum analyzer to check the harmonics properly.

anyone gone through something similar with a class C final like this?

yeah that ragged peak thing is pretty normal for class C especially with bipolars, the conduction angle being what it is means you're never gonna get a textbook sine before the filter. the LPF is doing the heavy lifting there. the real question is how steep your filter cutoff is and whether it's actually tuned right for 40m. a lot of homebrew LPFs get built to a standard design but the toroids dont always match their rated inductance especially if you wound them yourself on mixed cores.

if you can borrow a spectrum analyzer or even just check against a nearby receiver with an attenuator you can get a rough idea of how much second and third harmonic you're putting out. regs require at least 43dB down on harmonics for that power level so as long as youre in the ballpark you're fine. the waveform before the filter really isnt the thing to obsess over for class C, that's expected.

i had basically the same issue with a similar build last year. turned out one of my toroids in the LPF was wound with a couple fewer turns than it should've been, just miscounted while i was winding in a hurry. the output looked rough and a buddy let me borrow his SDR to sweep it and yeah there was a spike at the second harmonic that was way too high. rewound the inductor and it cleaned right up. might be worth double checking your turn counts and measuring the inductance if you have an LC meter or even just a bridge.