NOSValves Posted December 7, 2007 Share Posted December 7, 2007 Sorry for the delayed response lost track of the thread. Marty (Thebes) emailed me with a nudge So I take this noise is more or less about the same with no sources attached and not effected by the amps volume control? Also this noise is identical out of both speakers? How far away from the output tubes is this Triode/Pentode switch? One thing that happens when switching between these two modes is that the input sensitivty of the amp is lower in pentode mode as compared to Triode mode which makes pentode mode more susecptable to noise but usually this would be noise from outside sources connected to the amplifier. If the switch is half way across the amp noise can be the result but usually the mode of operation will not effect it much. I wonder if the contacts for pentode mode have become oxidized from a lack of use. Try working the switch back and forth vigorously (with the amp off). Quote Link to comment Share on other sites More sharing options...
Thuper Posted December 9, 2007 Author Share Posted December 9, 2007 The switch is on the back of the amp, between the speaker posts. So it's ca 4 inches from the output tubes. I have tried working the switch, but it didn't help. I've noticed that the amp is sensitive to radiation, so I thought I should make me a shielded powercord. I had the powercord from my DVD player running in front of the amp, with hum as a result... The powercord runs a inch or so from the Triode/Pentode switch. Quote Link to comment Share on other sites More sharing options...
Thuper Posted January 16, 2008 Author Share Posted January 16, 2008 The shielded powercord didn't do nothing with the hiss sound! Any other sugestions? Quote Link to comment Share on other sites More sharing options...
Cody_Mack Posted January 16, 2008 Share Posted January 16, 2008 In my experience, this same described noise was caused by noisy driver tubes in my Foreplay III; these are/were 12AU7A, not branded, that came with the kit. Was kinda weid though that they both started doing it at about the same time. Replaced them both (several months ago) and have not noticed that noise since. Rick Quote Link to comment Share on other sites More sharing options...
Thuper Posted January 16, 2008 Author Share Posted January 16, 2008 Well... I've changed the driver tubes. I have a pair og Sylvania and GE tubes here. And the hiss sound is there also when I use these. Frode Quote Link to comment Share on other sites More sharing options...
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