On 2/18/2010 5:07 PM, Ron Youvan wrote:
>
> The 8 Henry filter choke with an oil filled .1mFd in parallel then an oil
> filled 20mFd cap to
> ground is a tuned filter, tuned to 120 Hz. If you truly have 60 Hz hum, you
> have a diode open in
> one of the arms of the bridge rectifier. If you truly have 120 Hz hum, you
> have a "detuned
> filter" possibly the oil filled 20mFd cap has changed value. Check the
> values of both caps first.
> With this, like all power supplies the HUM sounds greater with a higher
> current draw, from the
> supply.
Be careful if you fix this. It's not tuned to *exactly* 120 Hz because that
would cause a
very high voltage to appear across the choke. Use the specified values if you
replace
anything.
Also -- if it's really 120 Hz. and not 60 Hz. that also rules out pickup from
the magnetic
field of the transformer somewhere in the audio chain, ground loops, etc.
--
Vic, K2VCO
Fresno CA
http://www.qsl.net/k2vco/
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