[sdiy] o-scope z axis control

[tpaddock at seanet.com]

I'd like to play with z-axis (brightness) 
on an o-scope that I'm using for X-Y 
display of audio. Such as brightness 
dependant on the x and y signals so 
it's brighter farther out from center. 
And it doesn't burn the center 
with no signal. So, as a starting point...

Could someone point me to a "precision 
full-wave rectifiers for dummies"?

I got a TEK 608 X-Y monitor at a ham radio 
swap meet Saturday. Differential inputs for 
X,Y,Z, whooo-hooo!

Almost got an old counter that used columns 
of lights for the display. Can't remember 
what that's called. 

Later,
Toby
Paddock