help with my humming valve amp

donny2pins · 11th January 2010, 06:48 PM

Hi everyone.have a problem with my valve preamp.the problem is that i am getting a loud humming from my horn speakers,and it has been getting louder over the last few months.i know it is a problem with the amp because i had a solid state amp that did not cause the humming.also when i put my hand on one of the external capacitors the humming dies down alot,i was thinking it was an earth problem ,can anyone help me pleeeeeease.

SY · 11th January 2010, 07:50 PM

Could be a lot of things. What sort of preamp is it? Do you have any experience with working on tube gear? Test equipment?

donny2pins · 12th January 2010, 07:26 PM

Hi sy,the preamp is a ming da mc7r

donny2pins · 13th January 2010, 07:39 PM

have just come in from long day out with family and sat down with a glass of red wine to listen to music ,as i put the preamp on i put my hand over the 2 left vales 12ax7, 12ua7 .as i did this the humming died down ,and here was me thinking it was the capacitors,that was because i had my hand over the valves while touching the capacitor. so now i am thinking it is not the capacitor but an earth problem.
the tubes are sylvania (baldwin) maching pairs .the strange thing is my old japanese tubes did not die down when i had my hand over them but the sylvania do ??? very puzzled indeed. i took the earth off the monoblocks but it made no difference so i put it back on. would love to hear any ideas .thanks.

11th January 2010, 06:48 PM	#1
donny2pins diyAudio Member Join Date: Dec 2009	help with my humming valve amp Hi everyone.have a problem with my valve preamp.the problem is that i am getting a loud humming from my horn speakers,and it has been getting louder over the last few months.i know it is a problem with the amp because i had a solid state amp that did not cause the humming.also when i put my hand on one of the external capacitors the humming dies down alot,i was thinking it was an earth problem ,can anyone help me pleeeeeease.

11th January 2010, 07:50 PM	#2
SY diyAudio Moderator Join Date: Oct 2002 Location: Austin, TX Blog Entries: 1	Could be a lot of things. What sort of preamp is it? Do you have any experience with working on tube gear? Test equipment? __________________ “Listening to records is like ****ing a picture of Brigitte Bardot.” - Sergiu Celibidache

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12th January 2010, 07:26 PM	#3
donny2pins diyAudio Member Join Date: Dec 2009	Hi sy,the preamp is a ming da mc7r

13th January 2010, 07:39 PM	#4
donny2pins diyAudio Member Join Date: Dec 2009	have just come in from long day out with family and sat down with a glass of red wine to listen to music ,as i put the preamp on i put my hand over the 2 left vales 12ax7, 12ua7 .as i did this the humming died down ,and here was me thinking it was the capacitors,that was because i had my hand over the valves while touching the capacitor. so now i am thinking it is not the capacitor but an earth problem. the tubes are sylvania (baldwin) maching pairs .the strange thing is my old japanese tubes did not die down when i had my hand over them but the sylvania do ??? very puzzled indeed. i took the earth off the monoblocks but it made no difference so i put it back on. would love to hear any ideas .thanks.

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