  We have observed a total of 67 pulsars at five frequencies ranging from 243
to 3100 MHz. Observations at the lower frequencies were made at the Giant Metre
Wave Telescope in India and those at higher frequencies at the Parkes Telescope
in Australia. We present profiles from 34 of the sample with the best signal to
noise ratio and the least scattering. The general `rules' of pulsar profiles
are seen in the data; profiles get narrower, the polarization fraction declines
and outer components become more prominent as the frequency increases. Many
counterexamples to these rules are also observed, and pulsars with complex
profiles are especially prone to rule breaking. We hypothesise that the
location of pulsar emission within the magnetosphere evolves with time as the
the pulsar spins down. In highly energetic pulsars, the emission comes from a
confined range of high altitudes, in the middle range of spin down energies the
emission occurs over a wide range of altitudes whereas in pulsars with low
spin-down energies it is confined to low down in the magnetosphere.
