Update: (Sounds Awesome) Tweed Super PT Specs Verification For KT66 Tubes

Discussion in 'Amps and Cabs' started by critter74, Dec 7, 2016.

  1. critter74

    critter74 Supporting Member

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  2. hogy

    hogy Member

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    KT66 draws 1.3A, 12AX7 draws 300mA., So total draw will be 3.5A. Transformer is rated at 4A. Marginal.
     
  3. critter74

    critter74 Supporting Member

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    OK, yes margiallly. Which I stated previously. My question was (or at least i tried to imply, maybe poorly) is if "marginally" is an issue for the PT and KT66 tubes.

    2 seperate but equal scenarios with "marginal" qualifiers:

    1. If I have $100 bill and I want to buy something that's $98, I can "marginally" afford it. But it doesn't matter as I have enough to cover the cost. With $2 left over for a lollipop.

    2. I want to drive somewhere that is approximately 495 miles away. With my car, I "should" have enough gas to cover 500 miles in my car. I should be able to make the trip, marginally. But things like traffic, uphill/downhill, wind draft, head winds, etc make that marginal more of a "better not chance it" scenario.

    So yes the PT @ 4A should "technically" cover it. Are there variables though that could but the draw well over the 3.5A? That's what I'm looking for.

    I've also found this site which has a plug and play formula, that seems to indicate that it "should" OK as all other specs are well within range as well:

    http://thesubjectmatter.com/calcptcurrent.html
     
  4. hogy

    hogy Member

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    The closer you get to the limit of the transformer, the hotter it runs. This can work for a long time.

    For the amps I design, I like to spec the transformer at twice the actual current draw. Not saying you have to.
     
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  5. Trebor Renkluaf

    Trebor Renkluaf I was hit by a parked car, what's your excuse? Silver Supporting Member

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    1.3A + 300mA = 3.5A? Must be common core math! :D
     
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  6. Humble Texan Fan

    Humble Texan Fan Member

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    The PT should be rated for continuous Amperes and in this scenario .5A is plenty of margin. Then the ouput power is bound to build up some heat as well, so it's not down to filament draw alone.
     
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  7. Pedro58

    Pedro58 Member

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    There's more than one of each type. The amp design isn't one KT66 and one 12AX7 only.
     
  8. Trebor Renkluaf

    Trebor Renkluaf I was hit by a parked car, what's your excuse? Silver Supporting Member

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    Where I come from 1.3A + 300mA = 1.6A, NOT 1.5A. But then I didn't take common core either. :D
     
  9. ked

    ked Member

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    Try this:
    3 x .300= .900
    1.3 x 2 = 2.6
    total ma= 3.5 A
     
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  10. Pedro58

    Pedro58 Member

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    Okay. Never mind, then.
     
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  11. hogy

    hogy Member

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    I assumed it was obvious that a Tweed Super uses two power tubes and three preamp tubes. Apparently not.
     
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  12. critter74

    critter74 Supporting Member

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    So I went ahead and tried thew KT66's... and it sounds awesome.

    I used a GZ34 rectifier. The sound did exactly what I was hoping for:

    Tightened the Bass for the better. 5881 and 6L6G/GC's/WB/etc made the Bass boomy and hard to manage, especially when using both the Normal and Bright Inputs. The Presence and Treble is also much more tame and less piercing and like the Bass easier to manage. Issues I thought were going to require a speaker change, seemed to be resolved with the KT66's. Before the Bright channel could have way to much sizzle and the Normal channel be way to dark and Boomy. Again, the KT66's seemed to tighten the Bass and mellow the very highs and just make it sound even better and more useful knob settings. Before it was a bit of a balancing act.

    Strangely the Mids (which are fixed on the Super) sound just right now too. Before I thought I might either have to add a Pot or change the resistor value. Now it seems to be where I like it (at least with my Tele's and Strats which I use 90% of the time with this amp).

    Overall its been a win. So unless some issue pops up, I think I'm going to use KT66's in this amp from here on out and use the 5881's I had been using on either my SF or BF Bassman's.
     
  13. Trebor Renkluaf

    Trebor Renkluaf I was hit by a parked car, what's your excuse? Silver Supporting Member

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    Doh! I see it now. I think I need glasses. :(
     
  14. makerdp

    makerdp Member

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    Hammond typically rates their transformers very conservatively. If you have a 0.5A margin with a Hammond you are completely safe.
     
  15. makerdp

    makerdp Member

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    Wow you waste a lot of money then. You only *need* about a 10% fudge-factor.
     
  16. GrungeMan

    GrungeMan Supporting Member

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    Ah yes, much gooder!
     

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