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Title: Need schematic for CKB-74028 frequency meter Post by: K1CWS on October 19, 2009, 06:20:57 AM I have just acquired a freq mtr that I'm am told is the NAVY version of the BC-221. But it runs on an external PS instead of batteries. And it has an internal modulator that the BC-221 doesn't have. My unit uses 6A7, 76 and 77 tubes. Hope someone has a schematic and/or a manual.
Title: Re: Need schematic for CKB-74028 frequency meter Post by: KE6DF on October 19, 2009, 08:44:54 AM I have one of those. You are right, it could be called the Navy version of the BC-221.
They are also called LM frequency meters. Yours is probably an LM-10 thru LM-21 -- one of the later units. You can find a schematic and info about power requirement in the Surplus Conversion Manual volume 2 which is available on the Web: http://www.mines.uidaho.edu/~glowbugs/SurpConv.html Each unit has it's own calibration book which fits in the slot at the bottom of the meter. The calibration manuals are different for each model and are have the serial number of the unit on them. If your calibration manual is gone, don't despair as I once found a program on the Web that would print out the appropriate calibration data for your unit if you plug in the serial number. Mine had the calibration book with it, so I didn't keep track of where that program was, but I suspect you can find it with google -- use "LM frequency meter" when searching as that's the more common name than the CKB number. Dave Title: Re: Need schematic for CKB-74028 frequency meter Post by: K1CWS on October 19, 2009, 01:48:58 PM Thanks Dave. I downloaded that info from Surpluss Conversion II and I saw that the PS connections were wrong. Wired it as per the schem and it works! It is within 100HZ @ 3885 by my freq counter. My unit is a LM-15 and I have the cal book. This will look gud in the rack with my BC-348 and ART-13. AMfone - Dedicated to Amplitude Modulation on the Amateur Radio Bands
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