Wanted to thank the many Reflector readers who responded to my
posting for an inexpensive low ohmage meter shunt. I was interested in
locating a low value resistor material easily manipulated and
calibrated to provide about .04+/- ohms. I wanted to shunt a typical 1ma
meter to read 1amp of plate current directly via the B- line. The
majority of responses basically suggested that I utilize the preferred
method of a 1 ma meter in the voltmeter mode. To accomplish this, I
could series install 1 ohm precision resistor in the B- line and then
wire in a rheostat across the resistor. This provides the means to
sample the voltage drop under load. Wire the rheostat to the meter to
complete the circuit and calibrate the plate current meter against a
known value. Suitable for many needs, but not quite what I was looking
for!
Coincidentally, I received an intriguing response from Colin,
K7FM that I was certain would be of interest to many amplifier builders
in similar meter calibration circumstances and should be shared. Colin,
apparently, had occasion to fabricate, as easily and inexpensively as
possible, a large number of same value precision shunts for a
specialized project. He discovered that a normal length of the typical
metal office paper clip consistently exhibited a low value of resistance
in the range of .02ohms. A double length of clip would easily suit my
.04ohm needs. Obviously, fractional parts of an ohm to achieve precise
current readings are achieved by tapping off along the clip's length. In
my QST Magazine article dated March, 2004 describing a process of
Rescaling and Customizing Surplus Meters, I used the tedious method of
shunting. Sure wish I had known of K7FM's technique at that time. Hope
this information helps. 73's Ron W2CQM/3
Epilogue: visit www.QRZ.COM/W2CQM for a listing of the most recent
articles authored by W2CQM.
For an update on the most recent Heath 6m dedicated retrofits, Drake
L4B/8877 project(s) ,and other amplifier related articles see
http://briefcase.yahoo.com/W2CQMron
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