I aligned an HRO-50, starting with the phasing capacitor half-meshed.
(don't trust the knob at "half", look to see
if the phasing capacitor is half-meshed, and adjust the phasing
knob to read "5" at half meshed).

You shouldn't have the BFO on, it will cause confusion.
Capcitively couple the signal generator at the grid
of the preceeding stage, and connect an oscilloscope
via a divide-by-ten probe at the plate
of the following stage.
(this avoids disturbing the crystal filter stage
with stray capacitance from either the signal generator or the 'scope).

Slowly rock the signal generator output, and look for the null
on the 'scope (AGC off, a.m. mode), with phasing capacitor at "5",
half meshed.

With my receiver, the null was at 457.0 KHz.

Then all the IF transformers were aligned, using a 457.0 KHz
signal from the signal generator. The BFO "0" (BFO cap half meshed)
was set at 457.0 KHz.

geojunkie wrote:

I am having a lot of trouble understanding the proper method to align
the crystal filter section (off the output of 3rd IF transformer)in an
SX-71. The manual suggests "rocking" the signal generator around the
IF frequency (455khz) while turning the IF transformer slug and
monitoring the output level to find a null between two peaks. You are
supposed to set the slug to the null. The output tone is to be created
using the BFO set for 1kz at the IF frequency. snip