Hallicrafters SX-28 Alignment Pages

If your radio doesn't pick up at least one station, you should go to the CPR page. You are not ready for this.

As of 28 August 2026, the main effort is still to complete this section. Current status of each part is given in footnotes.
Please explore and comment but don't get upset if you run across something stupid or just plain wrong.

This procedure has successfully aligned one early radio to the point it's working with 2‐4 µV antenna signals
on all bands with all selectivity settings including XTAL SHARP working as expected.

If you got sent directly here, you should check out the rest of the site. If you need help, it's available.

This is the top-level page for everything alignment related.
The pages are in multiple levels and categorized by functional blocks:

1. Measure - A procedure or page to determine a value
2. Test - A procedure or page to verify that something is working correctly
3. Adjust - A procedure or page check an operation and what to do if it isn't right
4. Theory - Notes on how it is supposed to work

Please note that the sections are presented in order - most important first.

Measure Crystal Frequency

The crystal is supposed to resonante at 455 KHz but like all components, it varies.
Knowing the exact resonant frequency of your crystal is critical to making the radio work as it's supposed to.

Follow the instructions here¹.

Adjust the IF chain

The IF chain, which consists of transformers T1, T2 & T3 and tubes V5 and V6, has four inputs:

    The cathode return voltage via R16 and R21.
    The screen voltage via R17 and R22.
    B+ via V18, R23, and R30.
    The output of the mixer V3 pin 3 via T1.

The IF chain must be adjusted to the same frequency as the crystal. If the crystal is way off frequency, this isn't going to work.

Adjust the Local Oscillator

The only inputs to the oscillator are the tuning capacitors and the band switch position.
There are two parts to this section: the 6 feedback capacitors C7‐C12 and the 12 frequency adjustments.

Feedback

Frequency

The adjust procedure is a cgi script that takes the crystal frequency determined above as an input and adjusts all the expected values for the different bands accordingly.

Test the AVC

The AVC is used in the procedures below as a measuring device. It uses two of the fifteen tubes in the radio. It's probably a good idea to see if it works properly.

Mixer

2nd RF