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Does the 6025 micro preamp tube work?

Discussion in 'Amp Central Station' started by chris m., Apr 14, 2021.

  1. chris m.

    chris m. Poster Extraordinaire

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    The DV Mark Eric Gales head features a 6025 micro preamp tube. Do you tube amp folks know whether these tubes deliver classic tube preamp gain response- clipping and compression that isn’t harsh— or are these things mostly hype and a marketing thing? After all, there are ways to use solid state technologies like FETs, MOSFETS , JFETS, op-amps, clipping diode pairs, etc., as found in analog overdrive and distortion pedals and many solid state amps to get good sounding preamp gain....
     
  2. Hari Seldon

    Hari Seldon Tele-Meister

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    I can't answer your question directly, but I have a couple of seymour duncan twin tube classic pedals that work with 6021 mini tubes.
    Alas, the pedals are crap, one transformer died, in the other the non standard pots are crackling and no cleaning helps.
    But: these sound heavenly with the mini tubes.
    I'm a tube overdrive gourmet and play only pedals with real tubes at high plate voltage. It has nothing to do with the tubes that they failed.
    So that's one example for great tone with mini tubes.
     
  3. TwoBear

    TwoBear Tele-Holic

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    I have one of those also that I lent a buddy and I got it back and it doesn’t work. When I bought it for next to nothing it seems somebody powered it with DC so I sent it to SD and they fixed it. I haven’t taken a signal generator to it (that’s about the extent of my Teknowledge) but my multimeter says the transformer is not blown. But back to the original question, I did sort of favor the clean channel over the dirty, but my thoughts on tube over solid state is that while I like them both I think the tube shines more if you’re into all the in between nuance when you roll back your volume. I haven’t had my twin tube working for a while but I seem to remember that preamp /tube would react that way. Sort of off-topic but I love transistor amps for jazz and where I want to sort of keep that same tone just louder and softer without it changing too much. And yeah the Dumble had FET switch on the front.
     
  4. Hari Seldon

    Hari Seldon Tele-Meister

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    No problem with a FET boosting the front signal, but overdrive has to happen in a tube.
    And some SS stages for level/impedance matching, reverb drivers etc. are also ok, as long they work in the clean range, no matter what the tube fetichists believe.
     
    mkdaws32 likes this.
  5. chris m.

    chris m. Poster Extraordinaire

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    I think overdrive does not have to happen in a tube to sound awesome. For example, the crunch I get out of an MI Audio Crunch Box into a clean Fender tube amp sounds awesome, and so does my EHX Russian Big Muff. For blues and classic rock a Tube Screamer into a clean tube amp also sounds quite good. But these class D solid state amps are different, of course. Not sure if the minitube sweetens and smooths the tone noticeably or whether it’s just for marketing purposes....
     
  6. mkdaws32

    mkdaws32 Friend of Leo's Gold Supporter

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    Yes - I’m generally a tube overdrive guy, but an MI Crunch Box or Suhr Riot into a clean SS amp is mind blowing for how tube like they are (for high gain). Best two MIAB pedals I have ever used, by far. The EXH Tortion is no slouch either for lower gain stuff. It’s a JFeT based preamp pedal and very tube-amp like.
     
  7. VintageSG

    VintageSG Friend of Leo's Ad Free Member

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    I don't know about that particular implementation, but the micro valves perform just as well as the normal sized counterparts, providing the support circuitry is up to snuff.
     
  8. Hari Seldon

    Hari Seldon Tele-Meister

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    Yeah, it's a matter of taste. Of course, if one likes fuzz, that's ok. It's only a different thing.

    I did a lot of side by side comparison and only the tube pedals had that dynamic, fat and transparent tone. There are a lot of great SS or FET pedals, but no of them has that transparency, like in a fine tube amp.
     
  9. chris m.

    chris m. Poster Extraordinaire

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    Clearly, "transparency" when it comes to dirt is in the ears of the listener....I've played just about every Holy Grail tube amp there ever was, at gig
    volumes, and I can say with confidence that for my ears I can get incredibly killer dirt tones across the range of gain I like to play from pedals going into
    a "clean pedal platform"-- at least a tube based one like a Fender DR or Twin Reverb. The nice thing about pedals is with a few different dirt
    drives you can sound like a Marshall, a Vox, an Orange, a Soldano, a Dumble, etc., without having to own multiple tube amps. Modern dirt drives
    are nothing like the Distortion +'s and DS1s of our youth....

    For me, though, dirt pedals do tend to sound better when they are going into a tube amp. Something about how they work together is pretty magical.
    11 Gauge talks about the magic of developing gain across multiple stages-- whether it be multiple pedals and/or multiple gain stages in the amp,
    and I'm a fan. Marshall does the same thing, albeit with tube-based circuitry-- but it's still the concept of multiple gain stages acting in concert to build
    the final gain structure. That's why guys like Jeff Beck will use a Klon into a Marshall-- because that extra, mild, non-tube gain stage makes the Marshall sound BETTER
    than it would all by itself. I know tons of guys in the hard rock era that had to die for Plexis and JCM800s, and yet they also very often used some kind of gain pedal
    in front to goose the amp and make it sound even better. In some cases it was just the boost you can get from a wireless setup or from an old Echoplex.
     
  10. 11 Gauge

    11 Gauge Doctor of Teleocity

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    Agreed on that.

    I couldn't find specs on the 6025 submini specifically, but it looks like a 6021 has about a gain of '30', if a 12AX7 is considered to have a gain of '100'. That's just a little higher than a 12AU7 (gain of '20'). And the 6112 supposedly has a gain of '70', which would make it roughly equivalent to a 12AY7.

    ...But to the OP's original question regarding how submini tubes are typically used - I don't think there would be much of an upside to just do some kind of 'starved plate' design like so many tube OD pedals do utilizing 12A_7s. Yes, their supply voltage requirements are lower than a 12A_7, but they actually draw as much or even more heater current. I haven't seen curves for the subminis (at least not recently), but was under the impression that they're similar to 12A_7s.

    Edited to add - it looks like the submini tube in question is actually a 6205. I think what applies to most other subminis should apply to them, as well. Here's a pic of one that I found:

    [​IMG]
     
    Last edited: Apr 15, 2021
  11. chris m.

    chris m. Poster Extraordinaire

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    Are you saying what I think you are saying? That in pedals for the most part these things glow but don't really do much? But perhaps in these Class D amps they actually do work properly since they would
    be plugged into 110V AC and could be properly powered? At which point how they overall circuit is designed determines how they contribute to the sound.
     
  12. 11 Gauge

    11 Gauge Doctor of Teleocity

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    Yeah, in many of the popular tube OD pedals, like the Butler/Chandler kind of stuff, the 12A_7 isn't really working as a pair of triode gain stages. I'm not even sure that the filaments even glow in something like a Tube Driver.

    The bigger point is that to get something like a 12A_7 to work as it does in the typical tube amp, it requires a supply voltage of typically no less than 120VDC. You're just not going to get the 'response' curves from them by operating them at lower voltages.

    ...But the submini tubes are different in that their supply voltage is not what's needed for your typical 12A_7 tubes. To that end, their curves should be similar to what you have with a 12A_7 operating within the optimal supply voltage range.

    That's probably the best high-level explanation that I think I can offer. Like a class D power amp, the submini tubes allow an amp designer a way to avoid bulky, heavy power supplies/transformers/chassis/etc., and in the process, potentially create a tube preamp with similarities to the old classic thing.

    It would actually be cool if Kingsley ever offered a submini tube pedal, because they might spur other builders to lean into the submini thing more.

    This thread almost has some very spooky timing, as I currently have a Siegmund Micro Tube DoubleDrive on my bench for repair. Apparently the builder passed somewhat recently, so I can't pick his brain! :(
     
  13. chris m.

    chris m. Poster Extraordinaire

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    Synchronicity
     
  14. Wally

    Wally Telefied Ad Free Member

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    The 6112’s gain factor of 70 is the same as a 5751 or 12AT7.
    @11 Gauge, what tube/s does that Siegmund unit use? I have some military NOS/NIB subminiatures. What rugged tubes....they are built to withstand 400-1000 G’s!!
    I see that the 6112 and the 6021 have max voltage of 250 and tests are done at the normal usage voltage of 100.
     
  15. VintageSG

    VintageSG Friend of Leo's Ad Free Member

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    There are voltage-voodoo methods that can be employed to kick a DC voltage up to 'interesting' levels. Have a look at the schematic for the Valv-e-Tiser for one method. Although not the 200V or more you'd expect in an amplifier, it's quite a respectable voltage coming off it. Also notice where the signal is taken from. A few valve based, low-ish voltage pedals are cathode followers. You get the clipping ( sort of ), the valve 'flavour' ( sort of ), and they can sound rather nice, with different clipping characteristics to a solid state diode clipper, or if the signal is taken from the ( starved ) plate, it may as well be a soft clipping diode for all the difference it makes. The Valv-e-Tiser is an easy build and a fine sounding pedal.
    There's valve based pedals, and pedals which have a valve in them. There's starved plate, low voltage devices which are sterile, devices which sound very good, and all points in between if you look hard enough.

    There have been pedals based around submini valves with voltage-voodoo circuits, just as there have been valve pedals that feature pukka painful power supplies. The devil is in the detail. My interest is piqued now, and I suspect a 6025 build will feature for me this year. It's not like I don't have enough half-built boxes of miscellany already.

    Thomas Blug has a floor-amp with a submini front end feeding a Class D stage. Have a look at Youtube videos featuring the BluGuitar amp. To my ears, across Youtube, it sounds authentic and impressive.

    Here's a submini used in an FX loop.

    https://www.tube-town.net/ttstore/kit-tube-fx-loop-6112.html
     

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