Strange noise

[enuenu]

My 3ch Dual recto started to sound very sick so I got it retubed and serviced. When I got it back it sounded greatly improved. However I have noticed that when I play a higher note at high gain settings, the note seems to have a bump in the sustain as it decays. It's like the note "breaks" just after you play it before resuming the liquid sustain. You can listen here;
http://www.adrive.com/public/YbkpZe/20130830_MesaTest_005.mp3

I can even see the bump in the audio track when viewed in my DAW.
I would think the note should decay nice and smooth.
Does this sound right to you?

I have also noticed that the amp is a lot noisier now with a hum evident. However as soon as I touch a metal part of the guitar the hum stops. I have tried this with two different guitars and leads.

PS - Is there a better way to post sound files on the forum?

 

[enuenu]

Note that the technician told me that he altered the bias by putting a resistor with a lower value into the bias circuit. The result was warmer running tubes and more gain. He said they were running too cold. Could this alteration have contributed to the perceived warble and flutter in the way higher notes decay?

The hum problem was 70% reduced by changing the computer style power chord that plugs into the amp. It seems that hot rodding the bias may have exposed this weakness.

The amp sounds great, except for the fluttering high notes.

 

[deeman]

My guess is that you may get some more hum with hotter tubes. Does the hum happen on all channels or just channel 3 on modern. I find theres always going to be some hum on modern due to the high gain.

Are you using the same outlet you used previously? If so, i'd contact the tech, there's got to be some warranty for repair work. Perhaps me missed a connection or something is loose.

 

[enuenu]

Hum on all channels to varying degrees. Changing the power cord made a big difference. However the power cord I removed never caused hum before so the hotter tubes must have affected the old cord somehow. Maybe the new cord has better shielding or something? I took it from my computer.

The note breakup is bothering me now. I am wondering whether to ask him to return the resistor that was in there before and run the tubes cold, even though he tells me there is no theoretical basis in electronics why you would do this. He changed the bias as he said you have to match bias to tubes. I didn't know he was going to do this. The tech is very well respected. I'm quite confused.

 

[enuenu]

I've read that the DR is designed to run a cold power section in combination with the very high level of gain coming from the preamp. Maybe lowering the bias to a level that would be normal in other amps has caused the problem.