why does 12u7 need certain amount of gain to stop hum 120???

prorms · 15th October 2008, 10:54 PM

why does 12ua7 need certain amount of gain to stop hum 120 hz ??
about 5% and up thd i do not hear the hum cycle .

Richard Ellis · 16th October 2008, 04:33 AM

Do you mean a 12AU7 right??
What circuit does it reside in?...I would guess the front end of an Amp or Pre-amp.
A 120 Hz audible hum is usually a power supply problem....Do you have a schematic we can all peruse??
______________________________________________Rick ..........

15th October 2008, 10:54 PM	#1
prorms diyAudio Member Join Date: Nov 2006	why does 12u7 need certain amount of gain to stop hum 120??? why does 12ua7 need certain amount of gain to stop hum 120 hz ?? about 5% and up thd i do not hear the hum cycle .

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16th October 2008, 04:33 AM	#2
Richard Ellis diyAudio Member Join Date: Sep 2006 Location: Mar del Plata, a BIG seasonal getaway city, can see the Ocean from our residence.	Do you mean a 12AU7 right?? What circuit does it reside in?...I would guess the front end of an Amp or Pre-amp. A 120 Hz audible hum is usually a power supply problem....Do you have a schematic we can all peruse?? ______________________________________________Rick ..........

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