[Amps] 120 cycle hum from Henry 2K-4

[Vic K2VCO]

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/