I saw some circuits that uses a emitter follower as a buffer for output. The emitter resistance is 470\$\Omega\$. The author says that, since the ac emitter resistance is very small, he put a 50\$\Omega\$ resistor in series with the output terminal, so that the circuit would look like 50\$\Omega\$ from the output.
But what I don't understand is, if you now connect the output to a 50\$\Omega\$ load, the emitter resistance then becomes (470\$\Omega\$ || 50+50\$\Omega\$) = 82\$\Omega\$! This could affect a lot of things, for example the collector current would suddenly change 5-fold, the signal source would see a 80% reduction of load, everything could go wrong. What am I missing here?