How about a TUBE Discussion

How about something audio related in the Club House....I have know for awhile all my 12au7 (maybe they are 12ax7....Im not sure) have an audible hiss when the volume in my pre is at any number above 0. What are some killer, super quiet tubes you guys would recommend?? NOS is fine, or maybe you have something that would fit the bill....

Comments

  • codycatalist
    codycatalist Posts: 2,662
    edited August 2019
    12AX7 has a much higher gain than 12AU7, does your Pre take both? If not I would do some research and ensure you are using the correct tube.

    I only have experience with common 12AU7 tubes but I liked the RCA Clear Tops and Philips JAN 5814s.
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  • mhardy6647
    mhardy6647 Posts: 32,926
    Tubes?

    https://youtu.be/rs9wuaVV33I

    B)

    OK, as implied above, the 12AX7 is a high mu tube (lots of amplification) -- so it does matter what your preamp is designed for, and how it runs the tubes in it. Hiss can come from other sources, too; do you "know" it's the tube or tubes? A classic source of hiss (white noise -- hey, that YT video of The Tubes isn't totally off topic!) is old carbon composition resistors. Folks like their tone ('specially for gee-tar amps) -- but they often don't age gracefully.

    It is possible that the preamp's gain is very high, so that the noise is accentuated (i.e., it could be an intrinsic "feature"* of the circuit).

    _____________
    * In the "Microsoft" sense of the word ;)

  • Nightfall
    Nightfall Posts: 10,042
    edited August 2019
    http://psvanetube.com/wordpress/store/products/shuguang-custom-12ax7-lx-special-edition-pair-low-noise-triple-mica/

    These Psvane/Treasure tubes are awesome. Super quiet, very good sounding, excellent imaging. Triple mica. $129/pair or $149/pair for hand selected that tested better than everything else in the batch.
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  • kevhed72
    kevhed72 Posts: 4,950
    Im pretty sure the hiss is the tubes, or at least the pre, since I took the pre out of the chain one day and the hiss disappeared. Also, according to the Cary manual it does take 4 12au7 tubes.
  • dromunds
    dromunds Posts: 9,969
    What 12AU7’s are you currently using?
  • mhardy6647
    mhardy6647 Posts: 32,926
    Four 12AU7s -- that's eight triode sections in toto! Dang, why do folks make their preamps so complex?!? :/

    Presumably whatever those four tubes are doing in the circuit, they're paired. From a troubleshooting perspective, it might be interesting to replace a pair at a time.

    Do you have a schematic or circuit description of the preamp in question? It might be helpful to plot a troubleshooting strategy.

    Frankly, I can't rationalize dropping nearly 300 smackers on a quad of modern production 9-pin miniatures -- but maybe all y'all have way more disposable income than I ever did.

    @kevhed72 I will check 12AU7 stock and see if I can send you a pair (if not a quad) of decent used 12AU7s to try out. I'll PM you if I can.

    Oh, and are "we" 100% sure that the four tubes all should be 12AU7s?

    The 12AU7 is a pretty middle of the road B9A base twin triode in terms of its properties (and IMO), FWIW.

    specs (12AU7A):
    http://www.tubebooks.org/tubedata/HB-3/Receiving_Tubes_Part_2/12AU7-A.PDF

    amplification factor = 19.5 for triode section 1 and 17 for triode section 2.

    compare those amplification factors to, e.g.,

    12AX7: 100/100
    6922*: 33/33
    12AT7: 60/60

    etc.

    _____________
    * not the same filament configuration as the others, but still in the family



  • dromunds
    dromunds Posts: 9,969
    As mentioned, replace a pair at a time. (perhaps its only one tube that is problematic.) (Its usually recommended to replace a pair at a time).
  • mhardy6647
    mhardy6647 Posts: 32,926
    dromunds wrote: »
    As mentioned, replace a pair at a time. (perhaps its only one tube that is problematic.) (Its usually recommended to replace a pair at a time).

    Yeppers. For best results, though, he's just gotta know/figure out which pair are a pair in the circuit. :p