Question about "preamp" tubes in the power section

Discussion in 'Glowing Bottle Tube Amp Forum' started by radiocaster, Apr 17, 2016.

  1. Silverface

    Silverface Poster Extraordinaire Platinum Supporter

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    Yes, but only buy from reputable sources. Not a cheap tube and notoriously noisy.
     
  2. Silverface

    Silverface Poster Extraordinaire Platinum Supporter

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    Yeah, that was a problem. Heatkit was one that provided detailed info. They specialized in home audio kits but offered a few guitar amps. Haven't seen one in decades - which probably is a good indicator of the quality of the finished product!
     
  3. mRtINY

    mRtINY Tele-Afflicted

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    Noisy enough that it's a problem for a drive stage? I understand why that's an issue when used as the first gain stage in a combo amp....


    -tINY
     
  4. Silverface

    Silverface Poster Extraordinaire Platinum Supporter

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    What do you mean? A "drive stage" generally means a gain stage. Or do you mean a "driver", aka "phase inverter"? An EF86 pentode is rarely used this way, and microphonic and white noise in the driver would be a huge problem - it's passing signal to the power tubes,a dn any extraneous noises will be directly injected into the power tube input grids.

    As a "preamp tube" - i.e.a traditional gain stage - the EF86 has great one IF it's a good tube. But the reason you see them used so rarely nowadays is because of the combination of microphonic and white noise (hiss) many suffer from. But when you find a good one I think it's one of the best gain stage tubes ever made.
     
  5. Ira7

    Ira7 Doctor of Teleocity

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    Wasn't it "Heathkit ?"

    Yeah, I'm old, and remember.

    It was Lafayette's brand, which was then an equivalent to Radio Shack.
     
  6. printer2

    printer2 Poster Extraordinaire

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  7. mRtINY

    mRtINY Tele-Afflicted

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    By drive, I meant to imply either the "power section" of a micro amp, or the last stage before the power tube in a bigger SE amp.

    I assume that signal-to-noise ratio is the issue - and putting a stage of triode gain in front of one would help.....


    -tINY
     
  8. radiocaster

    radiocaster Poster Extraordinaire

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  9. Silverface

    Silverface Poster Extraordinaire Platinum Supporter

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    Yes, obviously that was just a typo.

    A power tube can contribute noise, as can a phase inverter. It's not usually as significant as a preamp, but it can still be a problem.
     
  10. mRtINY

    mRtINY Tele-Afflicted

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  11. Johnny Cache

    Johnny Cache Former Member

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    Along time ago I saw a book on making an amp like that, would be interesting to build one.
     
  12. printer2

    printer2 Poster Extraordinaire

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    Why use an expensive tube that you will have a hard, expensive time getting an output transformer for? There are other easy ways to get the job done.
     
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