HRDx V1 going microphonic twice

Discussion in 'Amp Central Station' started by Offsetsand70s, Jul 27, 2021.

  1. Offsetsand70s

    Offsetsand70s TDPRI Member

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    I have recently bought a Fender Hot Rod Deluxe II. When I got it sounded a little muddy, and the first preamp tube seemed to be microphonic, so I bought a replacement 12ax7. Except that a couple of days into playing, and it seems that this tube has now also gone microphonic. It is in the v1 position. Any help would be greatly appreciated, or any advice on what the potential problem could be. Thanks!
     
  2. 11 Gauge

    11 Gauge Doctor of Teleocity

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    How are you confirming that V1 is microphonic? Are you tapping on the tube itself? If so, can you describe the sound? And can you confirm that none of the other tubes are making this sound when you tap them? You might also want to make sure the power tubes aren't making any noises, either.

    What is the brand of the 12AX7 you replaced, and what is the brand that you replaced it with?

    In the event it is actually two different tubes for V1 that have indeed gone microphonic, you may want to try a brand that's less prone to microphonics. I only have experience with one such 12AX7 - the Sovtek 12AX7LPS. 'LPS' stands for 'long plate, spiral filament', which seems to be key construction elements that reduce noise.

    Other than the 12AX7LPS, I personally don't have any experience with a single brand or model of 12AX7 that is less microphonics-prone, other than just trying to get my tubes from a source that screens out the noisy ones, or offers replacements on ones that do become noisy. Very generally speaking, the vast majority of JJ 12AX7s that I've owned have not been microphonic, with the exception of some that I had way back in the 90's (which is how and why I found out about the Sovtek 12AX7LPS).
     
  3. corliss1

    corliss1 Poster Extraordinaire Platinum Supporter

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    I like the EH12ax7, but I make sure to get the ones tested for low noise.

    In more modern versions of the amp, Fender includes a piece of foam around the preamp tubes to help with this issue:

    213095363_247657386869019_7099805144384131278_n.png
     
  4. schmee

    schmee Doctor of Teleocity Ad Free Member

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    What tube did you buy?
    I suggest buying the Mullard RI, haven't had a bad one yet of at least 20 tubes.
     
  5. Offsetsand70s

    Offsetsand70s TDPRI Member

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    I am tapping the tube and it producing a klink sound. There is also rattling that is audible once the volume is turned up enough. The first tube was JJ and the Second tube actually was a Sovtek 12ax7LPS.
     
  6. Offsetsand70s

    Offsetsand70s TDPRI Member

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    I have the foam around it in mine. The issue is more that the signal gets darker and muddy once the tube goes
     
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  7. corliss1

    corliss1 Poster Extraordinaire Platinum Supporter

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    It's always possible you just got a bad one too, it does happen. I'd try a third one, and then if that one gets weird in a short time, it might be worth a trip to the tech unless you're comfortable poking around in there.
     
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