i am prototyping an am transmitter on a solderless breadboard. im aware that with higher frequencies it has adverse effects on the circuit. i know that FM wont work. so i am wondering if there is a cut off frequency so i can say to myself " this circuit can be built on a breadboard, but this cant cause its too high". Thank you!

 

I don't trust breadboards with any digital signals in the MHz. Even if a microcontroller crystal oscillator "works" in the breadboard, I won't use it as I'm sure there are flaky things going on, including unknown and uneven loading capacitance. Important digital frequencies extend up to a few harmonics -- in PCB layout you use 10X; in high-speed matching you use ~3X -- so the same rule would roughly apply to analog, I would think.

 

That really is a tricky question. I have seen them work where it wasn't expected, which was a crystal oscillator at 32Khz.

Basically it depends, it is a judgment call, but in general audio and low frequency digital.