Tubes Asylum

Weird tube noise...

72.197.10.12

Cougar

A

from my 12AU7 tube. When I finished building Transcendent Sound Masterpiece 300 preamp, I had a scratchy type of noise from the right channel it sound like a bad pot and only made the noise when I turn up or down the volume, other than that it was dead quiet. So I lived with it until that same tube started to become noisy, I then switched it to the left channel and that weird noise followed the tube.

So I thought the whole time it was a defective pot (TKD) and was kind of pissed cause those pots are not cheap. I put in new 12AU7's (same brand) and its all quiet now no matter if I turn up or down the volume. I never had that happen before with tubes.

Follow Ups:

RE: Weird tube noise... - Triode_Kingdom 23:10:35 05/26/23 (6)
I would guess that it was oscillating. Does the preamp use grid stoppers?
- It was the tube. - Cougar 07:22:57 05/27/23 (5)
  tapping on it stopped the tube from being noisy. Also checked it with a scope when I completed the build to make sure it wasn't oscillating.
  - RE: It was the tube. - Triode_Kingdom 18:32:47 05/27/23 (2)
    You said: "only made the noise when I turn up or down the volume, other than that it was dead quiet." How could the VC make noise unless the tube was oscillating? Probably the measurement just missed it for some reason.
    - At first... - Cougar 18:49:40 05/27/23 (1)
      that tube would only make noise as I turn up or down the VC, once I stopped turning the VC it was dead quiet. Then after a few months of using it like that it started to make noise without moving the VC, it was a little crackling noise. I would tap on the tube to stop it from making noise. Then I moved the noisy tube to the left channel and the good tube from the left to the right, it did it with the bad tube the same thing in the right channel. Like I said at the first post I thought it was a bad VC that needed cleaning due to oxidation but it wasn't, it was the tube that why it was so weird.
      When I checked it with the scope after building it with 1khz and 10khz square wave and sinewave it was all good, no ringing or oscillation. That scratchy noise was always there from the beginning, I never saw it on the scope when I turned it up slightly when measuring it. All I know it was the tube and with the new tubes in there its all good even with the scope measurements. Well, its all fixed now and working fine. I was just wondering if anyone else had anything similar to what I had.
      
      Edits: 05/27/23
      - RE: At first... - Tre' 16:30:51 05/28/23 (0)
        
        In Reply to: RE: At first... posted by Cougar on May 27, 2023 at 18:49:40
        
        Whenever I run into a noisy VC that has been cleaned, I check the coupling capacitors. DC on a VC is always noise.
        
        Tre'
        Have Fun and Enjoy the Music
        "Still Working the Problem"
  - RE: It was the tube. - Jim McShane 12:00:17 05/27/23 (1)
    Just a reminder - if you are facing noise problems and you think it might be tube related check out my FAQ post. It may be helpful.
    - (Open in New Window)
    - I did check and... - Cougar 18:52:03 05/27/23 (0)
      cleaned re-tensioned the sockets, cleaned the tune pins, and checked for bad solder joints.

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