Which is mixer which is oscillator, etc?

[ducati2]

i am trying to learn FM alignment. I have purchased some great gear (sencore sg165, vtvm, signal generator, etc). but get stumped when service manuals refer to connecting to the mixer or oscillator. Mostly dealing with tube units, are there some general rules on how to determine which tube is the mixer or which transformer tower is the oscillator? Schematic does not always specify.

 

[Watthour]

Typically, the local / IF oscillator is upstream of the mixer, and the mixer blends that oscillator signal with the amplified incoming RF signal to create the IF. It might be helpful to locate texts on superheterodyne receivers for review, like this and others:

https://www.electronics-notes.com/articles/radio/superheterodyne-receiver/block-diagram.php

 

[dewdude]

On some tube tuners...the local oscillator and mixer are sometimes done on the same tube! This was more popular in the All American Five AM radios...but I've seen it done on others.

The LO will usually be connected to one gang of your tuning cap. This is because you're basically creating a resonant circuit with it. Another section is usually connected to the antenna for front end tuning.

Those will usually go different places but euventually run in to the same place at some point when they're mixed.

Dare I say itsi one of those thinfs you almost have to study a bunch of schematics so you can identify the numerous methods of doing it.