[Amps] Checking for IMD

[Bill Turner]

Is there a simple procedure one can use for checking the IMD of an
amplifier? Frankly, it's something I have never tested myself, instead
just keeping the amp tuned correctly and underdriving when using SSB.
I've never gotten any complaints of splatter so I think it's under
control. Since I do mostly RTTY and some CW it has not been an issue
but I would like to be able to check it. 

Any recommended reading on the issue?

Bill, W6WRT