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That is actually brilliant troubleshooting logic—and you are 100% correct about the design. On Band 1 (the AM broadcast band), the SX-28 completely bypasses the first RF amplifier stage (the first 6SK7) and routes the antenna signal directly into the second RF amplifier stage.
However, your choice of Band 1 actually reveals exactly why the radio is so deaf (35μV) and why your front-panel Antenna Trimmer knob feels completely disconnected from reality.
On Band 1, the 7 kHz IF error is working against you in a very specific, harsh way because of a component called the Padder Capacitor.
1. Why Band 1 is Suffering the Most from the 7 kHz Shift
Superheterodyne tracking relies on two types of adjustments: Trimmers (for the high end of the band) and Padders (for the low end of the band).
Because the AM broadcast band (550 kHz to 1600 kHz) covers a massive ratio of frequencies compared to the shortwave bands, the tracking must be absolutely perfect.
At 600 kHz on the dial, a 7 kHz error isn't just a tiny offset—it is a massive percentage of the total frequency.
If your IF is sitting at 462 kHz instead of 455 kHz, the Local Oscillator has to tune to 1062 kHz to hear a station at 600 kHz.
At those low frequencies, the Band 1 series padder capacitor (C28, a tunable screw located under the chassis) completely dominates how the radio tracks. If that padder is still set for a 455 kHz factory gap, it forces the front-end RF coils to look completely somewhere else, making the radio incredibly deaf.
2. Why the Antenna Trimmer is Dead on Band 1
If you look closely at the SX-28 schematic for the Band 1 switch positions, the front-panel Antenna Trimmer knob (C1) is physically disconnected from the circuit on Band 1!
Hallicrafters designed the radio this way because AM broadcast antennas vary so wildly in size that they relied on a heavy, fixed low-impedance primary winding on the Band 1 antenna coil to handle the match. The front-panel trimmer knob only cuts into the circuit on Bands 2 through 6 (the shortwave bands).
So, don't drive yourself crazy spinning that front knob on the AM band—it is doing exactly what it was wired to do on Band 1: absolutely nothing! How to Get Your Sensitivity Back on Band 1
Since you have your OWON generator and your custom microvolt attenuator hooked up, you can fix the Band 1 tracking directly by adjusting the low-end padder. Here is the exact dance to fix it: Step A: High-End Alignment (1400 kHz)
Set the SX-28 dial to exactly 1400 kHz.
Set your OWON generator to 1400 kHz with modulation turned on.
Adjust the Band 1 Oscillator Trimmer (C19, on top of the gearbox gear tower) until you hear the tone peak.
Adjust the Band 1 RF Trimmer (C6) and Band 1 Antenna Trimmer Chassis Screw (C2) for maximum volume.
Step B: Low-End Padder Alignment (600 kHz) — Crucial Step
Tune the SX-28 dial to exactly 600 kHz.
Set your OWON generator to 600 kHz.
Now, rock the main tuning dial slightly back and forth while adjusting the Band 1 Oscillator Padder (C28, accessible via a hole in the bottom chassis plate).
Keep adjusting that padder screw until you find the absolute highest peak of volume while slightly rocking the dial.
Because you shifted the IF to 462 kHz, that C28 padder screw is going to want to sit in a vastly different position than the factory factory settings. Once you dial that padder in to match your new IF gap at 600 kHz, your sensitivity on the AM band should instantly plummet from 35μV down into the clean, low single-digits.
Have you already tried adjusting the under-chassis padder screws during your alignment process, or have you mostly stuck to the top-side trimmer capacitors?
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Last modified: Sunday, 12 Jul 2026