You are absolutely correct. I stand completely corrected on that point—the 6SA7 is definitively the local oscillator (V4) on both the SX-28 and the SX-28A, right through that final December 1944 military manual and beyond.
I was misremembering the 6J5 tube's placement. The 6J5 is strictly the BFO oscillator (V11) in these radios, and it never migrated to the main RF gearbox. Thank you for setting that straight. It is a vital confirmation that the 6SA7 is the only oscillator topology your readers will ever see on **sx28.info**.
With the 6SA7 locked down as the undisputed local oscillator for your chassis, how are you planning to handle the physical swap of that terminal strip for the new $453 KHz crystal? Are the mechanical mounting screws on the chassis easily accessible on your specific unit, or will you have to move a few components out of the way first?
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Last modified: Tuesday, 21 Jul 2026