Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: theundeadelvis on July 30, 2010, 07:32:55 pm
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So, as I joyfully displayed in another thread (http://www.el34world.com/Forum/index.php?topic=9685.0), I just finished a new build, and I was enjoying it thoroughly until today I noticed a problem. When I play a specific note I get static. I can literally bend to this note, get static, release the bend, no static, bend, static, etc. Along with the static there's a bit of noise similar blowing across a microphone (muffled sound of rubbing something across a mic or blowing across it).
I tried a different cab, and I don't get it unless I push the external cab up against the amp, so I'm assuming it's related to the vibration that note produces. I haven't pulled the chassis yet to inspect it (cause I'm too bummed at the moment), but I'm wondering if anyones personal experiences may help me track down this noise. My ideas are:
-EF86 tube (actually a JJ EF806). It's mounted atop a silicon o-ring for to help, but maybe it's a bad tube, and I tapped the tubes with a chopstick and couldn't create the same noise.
-Vibrating leads. Haven't chopsticked yet, but maybe a moving wire
-Cold solder joint
-I thought it could possibly be a solder joint heating up hot enough to flow, but it does it as soon as you fire it up.
Anyone experienced this before? Anything sound more likely than another? Thanks in advance!
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Yeah, it can be a solder joint. I've that it happen before also on just "one" note & it was a solder joint.
Parasitic oscillation can be connected to a particular frequency also. I had that happen with JJ El84's & replaced them with Sovtek El84's and that problem was resolved.
Worse time was a resistor that was broken inside the enamel body. I finally found it by tugging on components with a needle nose pliars AFTER the amp was turned off and and the caps drained. Ironically, bass notes would cause the wire inside the resistor to open & close from vibrations. I can't begin to tell you how many hrs I spent tracking that one down. Replacing the resistor totally resolved the problem.
You'll get it fixed. You've already found a clue that it's mechanical due to vibrations.
With respect, Tubenit
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Well I got it sorted out. Once I button an amp up in a chassis, and call it done, I hate opening it back. That's usually when I post the "please tell me what's wrong, so I don't have to troubleshoot it myself" plea. But, I love this amp so much I wanted to be playing it ASAP, so I cracked it open and found the culprit quick.
It was a solder joint. I originally soldered the EF86 tube socket wires "lightly" b/c I thought I might have to de-solder them when I got my silicon o-rings to mount the socket on (but I didn't have to). So, one of the heater wires had come completely de-soldered, and was just floating in the socket pin. Soldered it in place, and noise is gone. Back to tone heaven!
Thanks Tubenit!