NOS/ANOS 5751 tube advice

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by BernardM, Jun 26, 2019.

  1. BernardM

    BernardM Supporting Member

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    Hi all

    I'm doing some more tinkering with my guitar rig and looking for advice on 5751 tubes for V1 of my Laney Lionheart amp, which sports alnico blue speakers.

    I'm looking for balance but with a lot of detail and presence in the top end when clean, and that 'sparkle' on edge of breakup. I get full drive sounds from pedals so these will be 'pedal platform' tubes rather than providing primary drive themselves (beyond edge off breakup).

    Thanks for any thoughts or advice on what I should check out.
     
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  2. pdf64

    pdf64 Member

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    It maybe helpful to give the experts some reference points. There are a lot of amp models out there, so a link for your amp’s schematic or at least the user handbook, what exactly have you tried / currently got in there, along with hour many hours approx use are on them.
     
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  3. ddog

    ddog Supporting Member

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    jan Phillips are old reliables...
     
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  4. BernardM

    BernardM Supporting Member

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    The circuit is a modified Vox type.
    I currently run an Amperex Herleen 12AX7 in V1, and black-plate Raytheons in V2 and V3.
    I love the clarity and crispness of sound they give but an just looking for an additional little bit of headroom that a 5751 would give, and also finer gain control on my drive channel (which I don't use driven hard, but rathe just edge of breakup sparkle).
     
  5. GuitarInnovations

    GuitarInnovations Member

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    Have you considered a Mullard 12AT7? Their NOS CV4024's may have what you're looking for.
     
  6. Tron Pesto

    Tron Pesto Member

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    12AT7? Unusual choice - have you had good experiences doing that? I'd like to hear about them.

    And this is not a setup - if you do a quick search about 12AT7 in critical audio tone positions (like V1 and even V2 depending), you'll get tons of hits about "12AT7s are horrible in V1 or anything other than a driver or phase inverter". It's such a prevalent thing that I couldn't tell you when I last tried something like this - if I ever have!

    Are there are theoretical reasons why 12AT7s don't "sound as good"? I guess. One could cite plate resistances and transconductances and current profiles/differences, but those ain't ears.

    I would love to hear about the results from someone who challenged this group-think.
     
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  7. easyed

    easyed Supporting Member

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    I've used these in a couple of application - preamp and reverb recovery - and never had a problem. The reverb recovery difference was remarkable, it quieted the hiss/hum in a Rivera era Concert. In V1 of a Super Reverb the 70% gain made the amp's clean sound clearer.
     
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  8. ddog

    ddog Supporting Member

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    Just read about what the plate resis (at7) doesn't lend it itself for v1 yesterday...don't need to go down that road I guess...but each to his own demise.
     
  9. slider313

    slider313 Silver Supporting Member

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    I would go with the GE 5 Star blackplate triple mica.


    [​IMG]
     
  10. Tron Pesto

    Tron Pesto Member

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  11. Timbre Wolf

    Timbre Wolf GoldMember Supporter Gold Supporting Member

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    I've auditioned quite a number of 12AT7 types as possible subs for 12AX7, and found all but one to be very thin, bright & plinky. The exception was the Mullard CV4024 made in the '80s (not any earlier CV4024). They have a thicker tonal character that is clear and lively. I consider them the one exception to the rule - don't bother subbing a 12AT7 for a 12AX7. However, in this case the OP wants sparkly detail in upper frequencies, and that's not what you'd get from '80s Mullard CV4024.

    @slider313 nailed it with the GE 3-mica black-plate 5751 - they're bright and clear, with somewhat thin bass.

    For a little more balance in the lower frequencies, my first recommendation is the 3-mica black-plate RCA 5751
    [​IMG]

    My usual precaution when using a 5751 to sub for a circuit designed for a 12AX7 is that attention must be paid to the change in feel, as much or more than the tonal changes. I've rarely kept a 5751 in such a position due to loss of dynamics. And using a 5751 won't provide any more clean headroom - it just enables you to turn up the volume knob a few notches before the equivalent level of overdrive becomes audible.
     
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  12. mrdannyboy

    mrdannyboy Member

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    I have a nice pair of Amperex which as I recall are from Endenhoven. They were new in the box and I just tested them in V1 of my Mesa and Ampeg. I believe they could be exactly what you are looking for. If you’re interested just shoot me a PM and I’ll send you pictures and so forth They have less than two hours on them. Beautiful tubes. Cheers
     
  13. tbonesullivan

    tbonesullivan Member

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    Best advice? Communicate with a reputable dealer and explain what you are looking for. Depending on how the preamp is designed, it may not give you the "extra headroom" you are looking for.
     
  14. Blue Strat

    Blue Strat Member

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    Most 12AT7s don't sound great to most people in 12AX7 situations. They tend to sound thin. CV4024s are a notable exception.
     
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  15. BernardM

    BernardM Supporting Member

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    Thanks as always for your generous and invaluable advice.

    I’m curious as to this loss in dynamics... is what you are describing akin to a kind of compression? I’d always associated use of 5751’s with SRV who was almost recklessly open, clean and dynamic in the way he set up his amps! Would be grateful for more detail of what you mean by this change of feel.
     
  16. Timbre Wolf

    Timbre Wolf GoldMember Supporter Gold Supporting Member

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    If you leave settings the same, the 5751 will render your amp relatively stiff, less responsive - with less compression. If you crank up the volume, then you're back to similar overdrive. But I've found that the flow/feel is still more clunky. Could be due to the optimization of the circuit for 12AX7. We don't all have a Cesar Diaz in our back pockets to adjust/optimize the amps.

    ALSO - there is no documentation stating exactly which 5751 SRV used in which position in which amp. So this really all comes down to each of us experimenting, and finding our preferences.
     
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