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How linear are Heathkit SB series LMOs?

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June 1st 08, 04:58 PM posted to rec.radio.amateur.boatanchors,rec.antiques.radio+phono

Chuck Harris Chuck Harris is offline

Chuck Harris is offline

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First recorded activity by RadioBanter: Jun 2006

Posts: 270

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How linear are Heathkit SB series LMOs?

wrote:
I just finished repairing an SB-301 receiver. It works well, however,
I can’t reliably calibrate the dial. For example, if I zero the dial
at, say, 3.5 Mhz using the internal 100 Khz crystal oscillator, the
needle is about 4 Khz too high at 3.6, 3.7, 3.8 and 3.8 Mhz, but is
again zeroed at 4.0 Mhz. Is this normal behavior for linear master
oscillators (LMOs)?

NOTE: This LMO needed to be repaired. Two of its tabbed slip rings
on the tuning shaft were “glued” together (hardened grease) and its
capacitor plates moved beyond the fully meshed position on the low end
of the tuning range. Anyhow, I removed and cleaned the slip rings and
adjusted the rotation offset of the tuning capacitor. I’m now left
wondering if, out of necessity, I fouled up the LMO’s calibration.

This is a manageable shortcoming, as I can calibrate to the nearest
100 Khz mark. Nevertheless, I’m curious if such variability is
normal.

The LMO was spec'd to be +/- 2KHz from end to end. So, set it to be
dead on at the middle of the band, and it should be fine.

Try googling on Heath LMO recalibration... You should find some instructions
on how to clean your LMO up, and recalibrate it for best linear operation.

-Chuck Harris

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