I've got a couple of designs for valve pantry transmitters, one by our own MurphyV310, but have never built them as I don't trust them as regards harmonics. I'm no expert — FAR from it — but I can't see anything that looks vaguely like a low-pass filter on them.
There was also a fearsomely complicated one using EF91s in the Bulletin a few years ago, though again no discernible LPF.
Maybe I'm paranoid but my understanding is that harmonics can travel further than the fundamental so for all that the later may not be getting far enough to be a nuisance and/or attract attention the former could well be.
Luckily most of the old wirelesses I actually use have got Gram sockets on so a DAB signal can be shoved up those.
— Joe
There was also a fearsomely complicated one using EF91s in the Bulletin a few years ago, though again no discernible LPF.
Maybe I'm paranoid but my understanding is that harmonics can travel further than the fundamental so for all that the later may not be getting far enough to be a nuisance and/or attract attention the former could well be.
Luckily most of the old wirelesses I actually use have got Gram sockets on so a DAB signal can be shoved up those.
— Joe
