Thanks ptrblck!  That worked.  It takes a little poking around to figure out the class structure, but not too much.  For example, using your example, I was able to use your example and this line:
encoder.encoder[1].mconv[0].conv.register_forward_hook(get_activation('B1(a).mconv.1D'))
to capture the output of the 1D convolution in the first block of a QuartzNet encoder model.
Again, thanks for the help.