Post by amakitalo on Apr 9, 2008 14:09:14 GMT -7
I bought a set of new tubes for my Route 66. Didn't need them but wanted to try a set of JJ tubes. Put them in, biased the amp and started playing. Sounds good, except there is a mechanical sounding (loose washers kinds of sound, high frequency) coming through my speakers.
I try different amps through the cab, the sound is gone. Try again with the Route 66 and it's there. Now this time I make sure that the head is isolated from the cab really well. Don't want to be fooled by mechanical vibrations. No, it's coming from the signal path.
I am thinking it's the new power tubes. Put the old ones in, bias the amp again (I am getting good at this), the sound's still there. Then I start thinking: I had recently swapped some of the preamp tubes with ones from my other amps, so I replace the EF86, voila the sound's gone!
All is well, right? No when I hit the strings hard I get this heavy distorted sound that doesn't sustain. It's kind of ugly distortion that you just know shouldn't be there and it sort of comes and goes. Then I remember that I also took what I know was a balanced PI out of the amp a few days earlier and replaced it with the one that probably wasn't balanced. Put the balanced one back in there and the tones are back without any unwanted distortion or mechanical sounds.
What really amazed me through this experience was that what sounded like a mechanical vibration was in fact caused by a bad preamp tube. Also, those balanced PIs can make a difference. I am a believer...
I try different amps through the cab, the sound is gone. Try again with the Route 66 and it's there. Now this time I make sure that the head is isolated from the cab really well. Don't want to be fooled by mechanical vibrations. No, it's coming from the signal path.
I am thinking it's the new power tubes. Put the old ones in, bias the amp again (I am getting good at this), the sound's still there. Then I start thinking: I had recently swapped some of the preamp tubes with ones from my other amps, so I replace the EF86, voila the sound's gone!
All is well, right? No when I hit the strings hard I get this heavy distorted sound that doesn't sustain. It's kind of ugly distortion that you just know shouldn't be there and it sort of comes and goes. Then I remember that I also took what I know was a balanced PI out of the amp a few days earlier and replaced it with the one that probably wasn't balanced. Put the balanced one back in there and the tones are back without any unwanted distortion or mechanical sounds.
What really amazed me through this experience was that what sounded like a mechanical vibration was in fact caused by a bad preamp tube. Also, those balanced PIs can make a difference. I am a believer...