How wrong can a guess be?
Totally? Thanks for helping a total newbie. 
There are no markings at all on the hall effect sensor.
I did some research and found what you described is as a
Common Emitter Amplifier circuit. I'm having trouble understanding
the math to size the resistors R1 and R2. Am I on the right
track with the circuit below? Can anyone help with the math or
sizing the resistors?
Here is a link to the page describing the Common Emitter Amplifier circuit.
http://webpages.ursinus.edu/lriley/ref/circuits/node4.html
And this one:
And one more: