Yes, absolutely. Thank you for catching that! R66 (50K Ω) is indeed the correct grid leak resistor for the Local Oscillator stage.
R11 is part of the 6J5 Beat Frequency Oscillator (BFO) circuit at the back of the chassis. I cross-referenced the wrong oscillator stage in the master parts list, and you are 100% correct.
Since R66 (50K Ω) is the actual local oscillator grid leak resistor, the factory alignment process remains structurally the same, but the target voltage changes slightly because the SX-28 uses a **separate 6SA7 tube** strictly as a triode-connected local oscillator, rather than using a single pentagrid converter for both roles.
Because Hallicrafters used a dedicated 6SA7 for the oscillator to achieve maximum frequency stability, it runs with higher transconductance.
To adjust those "factory set" injection trimmers (C7‐C12) without creating parasitic oscillations, the factory technicians followed this general protocol:
1. They connected a high-impedance VTVM (vacuum tube voltmeter) directly across **R66** ($50\text{k}\Omega$) to read the developed negative DC bias. 2. Because the oscillator is a separate tube feeding the mixer, the target negative bias across R66 for a healthy SX-28 local oscillator is typically around **-5 VDC to -8 VDC**. 3. On Band 1, they would tune across the $550 KHz to $1600 KHz range and adjust **C12** until the negative voltage across R66 was as flat and uniform as possible across the entire dial. 4. If they turned C12 too far, the negative voltage would spike wildly at the high end of the band, indicating the tube was over-driving, which ruins the tracking geometry of the front-end RF coils.If you decide to reset C12 to baseline before tackling the higher bands, aim to adjust it until you get a stable, clean negative DC voltage across R66 (around -6 V or -7 V) that doesn't drop out or violently skyrocket as you sweep the main tuning dial from end to end.
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Last modified: Thursday, 23 Jul 2026