[R-390] R390A Carrier Level Meter Question

[ToddRoberts2001 at aol.com]

In a message dated 8/23/2004 9:09:11 PM Eastern Daylight Time, 
DCrespy at aol.com writes:
Dennis,  

I assumed you were asking to decide on a substitute?  If so: the  problem is 
not the full scale current, it is the internal resistance of the  meter.  

Most 1ma movements are 100 ohms.  The R-390A needs (if I remember  right) 18 
ohms.  I have successfully used up to 38 ohm movements  with completely 
comparable results.  100 ohm movements just do  not work.  If you are 
thinking of 
shunting a meter, the problem is the  same.  Most 100 microamp meters are 
1000 
ohms, so shunted, you still wind  up with a 100 ohm / 1 ma meter!  The 38 ohm 
meters I have used  (International brand) had a series internal resistor, 
that 
when  removed dropped the meter resistance.

Good luck and have fun!  73

Harry  KG5LO
Saline MI 
Very good points Harry!  I had investigated using other meters in the past. I 
had determined that if you picked up a nice assortment of 100 and 50 microamp 
meters (usually at hamfests - 1 3/4" square size)  you would hit on one that 
had the right amount of internal resistance that could be shunted and end up 
with a 0-1ma movement with a resistance in the 18-40 ohm ballpark. From then on 
you would know  which scale and type of microammeter to be on the lookout 
for. Lafayette Radio used to sell a line of Argonne panel meters that would fit 
the R-390A front panel. ( 1 3/4" square size ) I have one R-390A with a 
Lafayette/Argonne VU meter that fits just right and looks very nice and appears to 
have the right sensitivity. That would be one meter to be on the lookout for to 
substitute as a line-level meter. 73 Todd Roberts WD4NGG.