Here is a collection of BC, LM and SCR Heterodyne Frequency Meter information.  If you have other links or documents, please email them to me so I can add them!  fbw4npn@gmail.com.   Some files are large .pdf’s and might constitute a slow download.
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SCR-211 Manual, all versions (large .pdf; slow download)
SCR-221 Manual (M version only)
TS-174B Manual (VHF version of the BC-221)

Frequency Meters as Master Oscillators
BC-221 (and similar) Output Voltage (WORD doc)

Frequency Measurement with the LM or BC-221, and some improvements

BC-221 as an Accurate Audio Osc (1962 “73” magazine, pg 35
BC-221 as a VFO (from QST)
BC-221 Quick Reference Frequency Chart (only for my BC-221)
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Using the LM-13 Frequency Meter As A VFO – 2 Transistor Buffer Amplifier and 1 to 2 Voltage Step Up Transformer Page
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Solid-State BC-221 (QST)
Solid-State BC-221 Feedback (QST)
More Solid-State BC-221 info (QST)
The Transistorized LM Freq Meter (non-destructive FET “tube” plugins)

BC-221-N Schematic & Voltage Table (probably similar for other versions)
BC-221 Extensive Information, Written by an Unknown Author (Download)
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