[ARC5] Changing LM Freq. Meter filament to 6 volts instead of 12/24

[Roy Morgan]

On Apr 16, 2008, at 11:49 AM, Tom Bridgers wrote:

> Does anyone have a reference on the steps to take to change the LM  
> frequency meters for 6 volts filament voltage?

This is a guess:

Get the thing out of the case and have a look at the changeable links  
on the back of the thing.  Read any labels.  Use screwdriver to  
change them.

If that does not work, go to BAMA:
http://bama.edebris.com/manuals/miltest/bc221/
OPS.. that is for the BC-221.

HERE is the LM frequency meter:
http://bama.edebris.com/manuals/miltest/lm18/

On page 8 the diagram indicates that you can use 12 volts or 24 (28) 
volts.  Not 6.3.  Note that this is the LM-18.  It's possible that  
some LM's were built differently.

Maybe your meter has been rewired for 6.3 (or 12.6) volts.

  The thing has three tubes. The type 77 and 6A7 are in series.  The  
type 77 and a 20 ohm resistor are in series.  These two arrangements  
are either both put across the filament line to ground for the 12  
volt arrangement, or put in series for the 24/28 volt arrangement.

My quick conclusion is that your meter has either been rewired for  
6.3 volts and 12.6 volts, or it was built the way you have found them.

What's the series number of the one you have (and others you have  
found for 6.3 volts)?

Roy,
Lover of LM and BC-221's

Roy Morgan
k1lky at earthlink.net
Lovettsville, VA 20180