[Rholbrook]

Hi everyone -- After I play my amp for about 45 minutes or more, the sound starts fading in and out, then ultimately goes quiet.  When I turn my amp off, the sound all of a sudden comes back for second while the power discharges.  If I turn the power back on, it starts playing normal for a while, then the same things happens all over again.  Any experience with this or suggestions would be appreciated.  For example, is it a grounding / ground loop interference issue?  FWIW, I am using a Synthesis tube amp coming from an Audio Note DAC / mac mini input.  Thanks in advance.

Richard

[Early B.]

I had this exact issue a few years ago with a tube CDP I own. The problem was resolved by changing out the Bendix tubes. I have no idea why, but those tubes sounded great, but were causing the CDP to run hotter than normal, and after a while, the sound would fade out. Did you make a tube change recently?   

[Rholbrook]

Sorry -- should have been clearer in my original message.  Yes, I did have the tubes changed a couple of months ago by the dealer from whom I bought the amp.  The dealer also cleaned the contacts, and I've checked to make sure that the tubes are firmly in place.  Given that the amp plays fine initially -- and again plays fine after I turn it off and on -- I wondered whether there could be some sort of feedback / interference issue going on. 

Richard

[FullRangeMan]

I had this exact issue a few years ago with a tube CDP I own. The problem was resolved by changing out the Bendix tubes. I have no idea why, but those tubes sounded great, but were causing the CDP to run hotter than normal, and after a while, the sound would fade out. Did you make a tube change recently?

Looks a cathode prob to me, sound would fade out if it becomes cold.
I wonder if this tube would be normal after the breakin period!

[Captainhemo]

When you had the tubes replaced, did you  keep the old tubes ?  You could try  changing back  to see if it  eliminates the probelm.  Would at least tell  you if it is tubes or not

-jay

[Ericus Rex]

Your issue is likely heat related.  Either component expansion is somewhere (even inside a tube!) causing an open circuit or the heat is changing the value/function of a passive component; maybe a cap in the power supply.  I once had a preamp that I left on all the time.  After a few weeks I noticed one channel not as strong as the other.  I took it in and the tech found no problem.  Brought it back home and it worked just fine.  Left it on overnight and same issue the next day.  Took it back to the tech (who was then quite irritated that I was 'making up this problem'), and told him to leave it on all night and then test.  He quickly found the cap that was changing value after heat-up and all was well.

Best of luck and keep us informed!