I think you have an EICO 369? It has one built into the output lead as shown in this diagram.
Now let's be clear - you will still get RF output without this resistor. You can still do an alignment without this resistor.
However, the get the best results (and keep your generator happy) you should use one. It will also mean your output level meter should be accurate,
Notice there is also a resistor and 1,000 pF capacitor inside the demodulator probe.
That's what Pentode was talking about adding. It's a low pass filter and will help remove noise if you have a fuzzy trace.
I'm not sure based you your scope screenshots if that's really what your trouble is.
