bad preamp tube?

pglbook
pglbook Posts: 1,979
edited February 14 in Electronics
A week ago, while warming up my amp and preamp, I noticed a high pitch ringing sound coming from the right speaker (even when I had the volume control knob of the preamp turned all the way down). It was not too loud but definitely noticeable. It had never done that before. The sound did not start when I first turned on my system but appeared some time later during the hour warm-up period. It lasted only 10 seconds or so and then disappeared and the system played fine the rest of the day. The sound resurfaced again last night while playing a Sam Rivers jazz CD; I could hear the high pitched ringing sound over the music. Again, it was not present when I first turned on the system but showed up about an hour or two into playing music. It lasted about 10 seconds and went away. And the system played fine - for the next 3 hours - the rest of the night without my hearing that sound again.

I am thinking that it could be one of the preamp tubes going bad. Would a bad tube make that sort of sound? How can I tell if a tube is going bad?

I have 3 tubes in my Eastern Eelectric MiniMax preamp - two 12au7 tubes and a rectifier tube.

Any other thoughts on what might be causing that sound?

Thanks.
Post edited by pglbook on

Comments

  • pitdogg2
    pitdogg2 Posts: 18,361
    Unless you have a tester the only way to know is put another tube in there that you know is good.
  • pglbook
    pglbook Posts: 1,979
    edited February 14
    pitdogg2 wrote: »
    Unless you have a tester the only way to know is put another tube in there that you know is good.

    Thanks. I plan to swap out one of the tubes today.

    The ringing sound just came from the right speaker so am I correct to assume that I should just swap out the right 12au7 tube of the preamp (there is a 12au7 in the right and middle position and a rectifier tube in the left position)?

    Or would it be preferable to swap out both 12au7 tubes?

    The nice thing about the EE MiniMax is that it does not require matching 12au7 tubes. Makes for great tube rolling possibilities.

    I have read that rectifier tubes rarely go bad so I will start with the 12au7 tube(s) and go from there.
  • marvda1
    marvda1 Posts: 4,303
    swap the tube locations and see if the noise follows the tube.
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  • audioluvr
    audioluvr Posts: 3,222
    I had a similar situation and when I swapped channels it followed and got noticeably worse. Put in a new tube and all is well.
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  • TroyD
    TroyD Posts: 12,393
    Rectifier tubes almost never go bad, like others have said....swapping out tubes would be the first thing I'd do...
    I plan for the future. - F1Nut
  • heiney9
    heiney9 Posts: 24,139
    I'll also suggest cleaning the pins. Many tube issues can be remedied my a good pin cleaning. Use a mild grit sand paper or steel wool and they De-Oxit.

    H9
    "Appreciation of audio is a completely subjective human experience. Measurements can provide a measure of insight, but are no substitute for human judgment. Why are we looking to reduce a subjective experience to objective criteria anyway? The subtleties of music and audio reproduction are for those who appreciate it. Differentiation by numbers is for those who do not".--Nelson Pass

    Pass Aleph 30 | EE Avant Pre | EE Mini Max Plus DAC | MIT Shotgun S3 | MIT Z P/C's | updated SDA 1C| SQ Box Touch/Welbourne Labs P/S- Tubes add soul!
  • pglbook
    pglbook Posts: 1,979
    edited February 15
    I swapped out the right 12au7 tube and played music for 4 or 5 hours yesterday and everything was fine. Time will tell but it seems like that solved the problem.

    Thanks to all for the feedback.
  • pglbook
    pglbook Posts: 1,979
    edited February 15
    heiney9 wrote: »
    I'll also suggest cleaning the pins. Many tube issues can be remedied my a good pin cleaning. Use a mild grit sand paper or steel wool and they De-Oxit.

    H9

    Thanks, Brock. That is a good idea about cleaning the pins.
  • pitdogg2
    pitdogg2 Posts: 18,361
    heiney9 wrote: »
    I'll also suggest cleaning the pins. Many tube issues can be remedied my a good pin cleaning. Use a mild grit sand paper or steel wool and they De-Oxit.

    H9

    I've found stainless steel brushes very good for this. My stainless steel brush is 1" wide and 3" long does a great job. I then use a old tooth brush that i put De-Oxit on and run over the clean and shiny pins. It leaves just enough to cover the pins completely.
  • Nightfall
    Nightfall Posts: 9,426
    TroyD wrote: »
    Rectifier tubes almost never go bad.

    See @pitdogg2 ?? WTF I churn through them.
    afterburnt wrote: »
    They didn't speak a word of English, they were from South Carolina.

    Village Idiot of Club Polk
  • pitdogg2
    pitdogg2 Posts: 18,361
    edited February 15
    Eventually they all go bad. Depending on how the tube is used in the circuit will depend on how long they last. I've had folks tell me that the mullard rectifier tubes never go bad I kind of find that hard to believe myself.
  • invalid
    invalid Posts: 517
    Nightfall wrote: »
    TroyD wrote: »
    Rectifier tubes almost never go bad.

    See @pitdogg2 ?? WTF I churn through them.

    If a rectifier tube is going bad often something is wrong with the amp or preamp. Rectifier tubes do wear out but they usually outlast the other tubes in the gear they are in.
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