[R-390] 390A Line Level meter replacement..?

[Jacques Fortin]

Hello Doug,

OK for the 50mV, but this is not very useful in absolute terms.
The two values needed to characterize a basic meter are the full-scale
sensitivity in amperes (like 1mA) and the movement resistance value, Rm.
The voltage developed across the meter at full-scale is the product of those
two values, Ifs x Rm = Efs.
Problem of knowing only the Efs is that it can be the product of many
combinations...
BTW, the reason why it is so hard to find substitutes to the R-390(A)
original Carrier Level meters is their uncommon combination of values.
The full-scale current value is 1mA, a fairly current sensitivity, but their
movement resistance is only 18 ohms, making the meter full-deflect for only
18mV across !
This is due to the high intensity of their internal magnet.
This also explains why some current 1mA, 100 ohms meters cannot be used as
substitutes without a form of external amplification.

73, Jacques, VE2JFE