[mythtv-users] Hum on analog audio to TV

Don Lewis dl-mythtv at catspoiler.org
Sat Oct 25 17:37:46 UTC 2008


On 25 Oct, Allen Edwards wrote:
> They don't build them that way any more.  They used to put capacitors from
> each side of the outlet to the chassis for RF suppression.  The problem was
> that this put the chassis at 55 volts.

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 think a lot of the DC
supply voltages were just supplied by rectifier connected to the power
line, and the rest were probably supplied via the horizontal sweep
transformer.  The cases were plastic, and the volume and tuning knobs
were insulated via plastic shafts.  The antenna and antenna inputs were
isolated by connecting them to the tuner input through an RF balun.

Most tube radios were designed this way as well.




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