"Andy Cuffe" wrote in message
...
I had my fluorescent work bench lamp apart today to try to stop an
annoying intermittent buzz from the ballast. It's a typical two 15W
tube with separate series inductor ballasts for each tube.

I was surprised to see a 4.7uF cap in series with one of the ballasts,
but not the other. I'm wondering why they would have put a cap in
series with only one ballast? The only thing I can think of is that
it might cause one tube to operate 180 deg out of phase from the other
to reduce flicker.


That's exactly what it does, this is a lead-lag configuration, the tubes
flicker alternatly to reduce overall flicker. The same basic arrangement is
used in preheat F40 twin tube ballasts.