Barebone mono tube preamp?

Discussion in 'The Projects Forum' started by johnsy, Jul 16, 2014.

  1. johnsy

    Thread Starter New Member

    Jul 3, 2014
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    Hi,


    does anyone have knowledge of mono tube preamps without semiconductors and transistors?

    Years ago someone mentioned building a few in a japanese magazine (don't remember the name)

    I remember one picture of a (very) small metal box with a single tube.


    Does it sound feasible?



    Johnsy.
     
  2. GopherT

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    Nov 23, 2012
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  3. johnsy

    Thread Starter New Member

    Jul 3, 2014
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    Thanks a lot! this is a nice introduction to tubes.

    If you get the name that would be great.

    I just want to add that one of the preamp in the magazine was listed as "tube preamp mono MIC" by the author.

    Most mono tube preamp are tube boosters - overdrive, distortion effects which was not the case of the author preamps.
     
  4. MrChips

    Moderator

    Oct 2, 2009
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    I think I can achieve the same thing with a FET and a 9V battery.
     
  5. johnsy

    Thread Starter New Member

    Jul 3, 2014
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    I'm sure but it wouldn't glow!


    I'm well aware of the solid states vs vacuum tubes debate but as i have access to a selection of tubes it might be a good afternoon project.

    So if anyone as a schematic (or informations) on (small) tube mono preamp (mic), this will be greatly appreciated!
     
  6. alfacliff

    Well-Known Member

    Dec 13, 2013
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    you might want to search "glowbugs" for tube projects.
     
  7. bertus

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  8. BeerBelly

    New Member

    Dec 16, 2013
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    What kind of tube amp were you looking for?
    Something to drive a speaker?
     
  9. THE_RB

    AAC Fanatic!

    Feb 11, 2008
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    So you need a FET, a 9v battery and a LED!
    ;)
     
  10. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    Nah, RB. Use the FET amp, but replace the LED with a tube to keep the punters happy. :)
     
  11. johnsy

    Thread Starter New Member

    Jul 3, 2014
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    Thanks, didn't know this (it brings up a lot of very interesting pages)

    Thank you! what a find, browsing through this is gonna take some time!

    A single tube mono preamp, Yes.

    I guessed that choosing a mono mic preamp instead of stereo would have been be a nice introduction to the world of vacuum tubes , but strangely it proves more complex than i thought.

    Alright but where is the warmth? not led size but doesn't take much space:


    [​IMG]

    "Sub-miniature tubes"
     
  12. BeerBelly

    New Member

    Dec 16, 2013
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    Well as an introduction to tube amps.
    A single tube will probably not have enough gain to drive a speaker from a microphone. Also a transformer is needed at the plate of the tube to match its impedance to the speaker.
    Tubes require a higher voltage than most modern electronics and another power source to heat the filaments.The EZ81 tube can be replaced by a 1N4007 diode to simplify things if you wish. The dual control is just a tone control.
    A well stocked junk box of older parts may be needed.
    [​IMG]
    Here is the source of of this schematichttp://www.angelfire.com/vt/audio/
     
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  13. bertus

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  14. johnsy

    Thread Starter New Member

    Jul 3, 2014
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    Thanks for the schematic and link!

    Not too sure about that one, more details on this can be found in the "Vacuum Tube theory & circuit design" section of TBO (thanks again bertus!)

    To be able to fit everything in a small enclosure i might have to look for a hybrid amp (the transformer is an issue and will also require a separate enclosure)

    Even if i don't have sub-miniatures tubes, i'll look into the schematics (and size)


    [​IMG]

    At this size transformer(s) are not an issue!


    Once again thanks a lot bertus!

    I think that with all that i got everything, i will check the tubes i have for specs and if i have premium tubes in the collection!

    It looks more like a weekend (or even a week) project, than an afternoon!
     
    Last edited: Jul 17, 2014
  15. johnsy

    Thread Starter New Member

    Jul 3, 2014
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    For those also interested by the subject (but a bit overwhelmed) i found this page with a lot of details (but clearly presented) including a list of preamp tubes, which help!

    About sub-miniature vacuum tubes in particular:

    The cheap k261 valve preamplifier kit from oatley is worth looking into.

    [​IMG]
     
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