[sdiy] more power questions

[Mountain Man]

Like Rob, I've been working on circuit power this weekend.  I've put
together a 7812/7912 circuit, intended to daisy-chain off my 9700 supply
(and killed the 9700 power supply in the process :(    Anyway, I have the
supply working, but studying it's behavior in light of the discussion a
couple of days ago has raised a bunch of questions for me.

After the discussion about needing more than 12V, I thought, "hmm, I wonder
if the 12V AC wall wart that I'm powering off of is supplying enough?
Hooked it up to my voltmeter - 14.7V.  That's not 12V.  That's not even
within 20% of 12V.  Not that I'm complaining, I'm getting extra power for
"free" <g> ... but I am curious.  What's the story on "power ratings"?

I have the "12V" AC feeding a pair of power diodes (1N4003).  When I
measure the (DC) voltage at the other end of the diodes (using ground
coming from between the caps in the 7812/7912 circuit) I get +18.2 and
-19.2.  What causes the voltage increase?  Is the difference between the
two simply due to mismatched diodes (not a problem, but I'm curious  :)

I hooked my scope up to the output of each diode in turn (using my grabber
hook attachment - thanks, folks!).  I expected to see a series of "M"s (or
"W"s).  What I'm seeing is a flat line, with upward "bumps" every 18 msec
(must be 60Hz!  I think I'm getting the hang of this scope :).  The bumps
are about 2msec wide, and 1.5V high.  When I check negative, I see downward
bumps a little less wide, and .5V.  Why is so much of the cycle at 0V?  Why
are the + and - peak voltages a factor of 3 different from each other?  And
why is the peak voltage I'm seeing so low, particularly given the DC
voltage readings?

BTW, I *am* still learning to use my scope (and I suspect will be for a
while :)   I'm using the "holdoff norm" control to get the waveforms to
"hold steady."  I'm unable to prevent a small amount of horizontal drift,
however, which makes measuring time a pain.  Is there a trick to this?

Thanks much,
Elby