[mythtv-users] Hum on analog audio to TV

[David Brodbeck]

On Sat, October 25, 2008 10:37 am, Don Lewis wrote:
> Even worse were the old transformerless tube sets.  One side of the
> chassis was connected directly to the side of line cord that was
> hopefully connected to neutral.  The tube filaments were all connected
> in series and across the power line input.

I have a tube radio that was originally wired this way.  The kicker was
the whole bottom of the radio was a metal plate!  To make matters worse,
the switch was in the chassis side of the line cord, so there was no
"right way" to plug it in -- either the chassis would be hot with the
radio off, or it would be hot with the radio on.

I guess they just hoped everyone would unplug the radio before picking it
up -- or that they'd stick to using the handle on top.  I can only assume
product liability was not a concern in 1949. ;)

Incidentally, many TV sets still use transformerless designs internally,
so if you decide to repair your own TV, be careful when you're poking
around in there.  And be *very* careful where you connect your
oscilloscope's ground probe.