Some tube advice on 12AT7WC-EH vs 12AT7EH

Discussion in 'Amps and Cabs [BG]' started by therealbigsteve, Jan 25, 2015.

  1. I'm trying to get a little more headroom from my YBA200-2 head and I was wondering which of these tubes y'all would go for in the V1 section(stock setup is V1-12AX7, V2-12AX7, V3/Splitter 12AU7, the 12AX7s are Sovteks and the splitter is an EH). The 12AT7WC caught my eye first but I was wondering if it would make a difference compared to the older model (12AT7EH). The 12AT7WC has short plates to help reduce microphonics and noise. The 12AT7EH is said to have a deep low end response thanks to the long plate making it an excellent choice in reverb driver and phase inverter stages. However, use in high gain preamp stages is not recommended due to potential microphonics. Would reduced microphonics be something I want? I like the EH tubes and I plan on replacing all the stock tubes entirely with EH tubes by the middle of summer.
  2. Bassmec


    May 9, 2008
    Ipswich UK
    Proprietor Springvale Studios
  3. christw

    christw Get low!

    May 11, 2008
    Dayton OH
    I would stick to the tube type the amp was designed to run. Changing V1 might change the preamp overdrive characteristic a bit (where on the knob it breaks up) but will not net you more headroom from the power amp.
    B-string likes this.
  4. B-string

    B-string Supporting Member

    In addition to this, the sonic character of a 12AT7 is one I have not liked at all. Sharp, cold and course. 12AY7 or 12AU7 are better IME, but still just delays by knob position where the power amp section runs out of gas.
    BurningSkies and christw like this.
  5. christw

    christw Get low!

    May 11, 2008
    Dayton OH
    +1 the 12AT7's overdrive characteristics are also different than the 12AX7's. Harsh would be the word I'd choose, nowhere as pleasant IMO/IME in both bass and geetar amps.
  6. waltdogg


    May 24, 2014
    If your amp calls for a 12AT7, try a JAN Philips. NOS, USA made. Usually as cheap as new production 12AT7s. The new production Tung-Sol is good but it's more expensive and a lot brighter. I use the JAN Philips 12AT7 as my phase inverter to get more Marshall out of the power section of my Science Hellhawk.
    Last edited: Jan 28, 2015
    therealbigsteve likes this.
  7. waltdogg


    May 24, 2014
    Wouldn't use it for V1 though. Try a Tung-Sol or gold pin EH or gold pin JJ.
  8. ThisBass


    Aug 29, 2012
    Unless the schematic itself is changed to achieve more headroom which than is nothing but a gain reduction its doubtful to achieve a gain rduction by rolling slightly different tubes. However sometimes a wrong tube at a wrong place may cause an increased or decreased gain (different headroom), but it depends! E.g. if 12AX7 id replaced for 12AU7 may cause a different gain factor, bur it depends on the schematic itself if this than really happens or if not
    Coolhandjjl likes this.
  9. beans-on-toast


    Aug 7, 2008
    There are a few options that can help you tune up your amp and get the most out of it.

    - How old is the amp? If the power supply caps are not performing up to spec, this can result in a loss of headroom and an earlier onset of distortion. If they haven't been changed in 8-10 years, this is a possibility.

    - Has the bias of the power tubes been checked recently? The bias can drift and should be checked yearly if the amp is in regular use.

    - Tubes are another possibility. Some small signal tubes (12AX7, 12AU7) have more headroom than others. But you can also specify late onset of distortion when ordering the matched and balanced power tubes. This will give you more headroom.
    Last edited: Jan 25, 2015
    therealbigsteve, 96tbird and ThisBass like this.
  10. Sorry I haven't been back to reply. I got real busy after I posted this. There is a ton of threads and it's a well known fact you can swap out the tubes in the preamp section of the YBA200 to achieve more clean headroom. There are a few different mod options. The easiest is the one is what I'm about to perform by just changing out the V1 from a 12AX7 to a 12AT7. Another is changing the V1 to a 12AY7 and in the V2 to a 12AT7. Some people even swap out both 12AX7s for 12AT7s in both the V1 and V2 spot. It's been documented. I can post links if you want....I was really seeing if anyone can tell me about the specific difference between the 12AT7EH and the 12AT7WC and which one would work the best out of these two...right now my head breaks up to early in my opinion it getting one of these no matter what. Also when the weather gets warmer and I get more $$ its getting a full set of new tubes in the power section as well as a full check up.
  11. ThisBass


    Aug 29, 2012
    If I felt unhappy with an amp due to a specific lack like too much gain or decreased headroom I'd try to mod the schematic instead of rolling different types of tubes which in worse case may heavily displace the biasing (quiescent) point of a tube output stage.

    V1a: kathode basis stage
    V1b: kathode basis stage

    V2a: buffer stage
    V2b: kathode basis stage

    I did not do the math but a reverse system ECC832/12DW7 for V2 should work well! But I have no idea if a reversed 12DW7 on V2 will really solve your problem.
    Reverse system 12DW7 means:
    System #1: 12AU7
    System #2: 12AX7

    for the record, the stock 12DW7 is of:
    System #1: 12AX7
    System #2: 12AU7

    IMO to fix your problem that's work for a qulified amp tech.
    Last edited: Jan 26, 2015
  12. ThisBass


    Aug 29, 2012
    Overdrive characteristic may also be tweaked by providing an asymmetrical bias point.
    Lots of amp designers use this design feature to generate a specific amount of even harmonics.
    However there is actually a kind of sweet spot to hit the best performance of musical sounding overdrive charateristic.
    Far too much "displaced" biasing point (mostly) generates a hazy blumed sound.
  13. SteveCS


    Nov 19, 2014
    Hampshire, UK
    Like many tube amps, the gain control on the YBA200 is after the first gain stage and is not a gain control but an intermediate volume control affecting only the input level to stage 2. Is it possible that your input signal is too strong (active bass or boosted from a pedal board) and that you are already driving the first stage into some level of saturation?

    I would investigate this before shelling out on new off-design tubes that could create more problems than they solve.
    therealbigsteve and ThisBass like this.
  14. Steve Dallman

    Steve Dallman Supporting Member

    Looking at the schematic, V1 is pretty standard stuff. From experience, a 12AT7 or 12AU7 would likely sound dull and lifeless. I'd try a 12AY7, which will have similar characteristics to a 12AX7 but with lower gain.

    But the range of gain and response among different types and brands of 12AX7's is pretty wide. Tone ranges from pretty dark to bright and even too bright/brittle. Gain will range from very sensitive and higher gain to lower gain closer to a 12AY7.

    Many tube vendors and websites give individual tube characteristics. Groove Tubes used to give pages of info on the rebranded tubes from different manufacturers they sell. If you are interested in JJ's a call to Bob at Eurotubes will get you a lot of info. Tell Bob what you are looking for and he'll give you his well reasoned opinion.
    therealbigsteve likes this.
  15. I have one bass that is full blown active (pickups and preamp) and my other one has passive pickups and an active preamp. The problem is with both. my band is loud and I really need to crank this amp through my NV215. I just want less breakup while doing that.
  16. SteveCS


    Nov 19, 2014
    Hampshire, UK
    Looking at the user manual for your amp, the gain control is designed to give "a warm overdriven tube sound when turned up (even at low volume levels)."

    I use a Kittyhawk Quattro Tube preamp for the 'high' side of my Stick, and the clean channel input stage is almost identical to that of your Traynor (thx to ThisBass for the link to the schematic). With the instrument on full, the clean channel stays clean up to about 8/10 on the knob - after that there is a little bit of 'crunch'. However, I also know that even with the clean gain turned down at 4/10 I can get crunch on the clean channel by clean-boosting the input level. This breakup has to be coming from the input stage. I suspect your amp is no different.

    You could try a lower-gain tube in the first stage, but whilst it will probably clean up the pre-amp stages I doubt very much if it will help you find more overall clean volume. You could try the following;

    1. Turn the instrument volume to 0, gain to 10, EQ flat and master volume to something sensible
    2. Gradually turn up the instrument until you start to hear crunch.
    3. Reduce the gain until the crunch goes away then increase instrument volume until it comes back.
    4. Continue reducing gain and increasing instrument volume until you cannot get back to clean. Now you have found the input level at which stage 1 is breaking up, i.e. you have found maximum stage 1 headroom.
    5. Now gradually increase the gain until the crunch just comes back - we know that stage 1 is clean so this has to be second stage breakup - you have found maximum stage 2 clean headroom.
    6. Adjust EQ to your liking. If you hear crunch, back off the gain until it goes away.
    7. Increase Master Volume. If you hear breakup it is from the output stage. Back off MV to clean. Your amp is now at maximum clean. If you still don't have the required volume, a low-gain input tube won't help. It might be time for a slave amp and more speakers (or a quieter band!).
    therealbigsteve likes this.
  17. ThisBass


    Aug 29, 2012
    If the overload occurs at the grid of the initial stage due to excessive input level then it will be impossible to fix the problem with different gaining tubes. Overload at the grid (the well known grid limiting) is widely independent of a tubes gain. Grid overloading is well reinforced by the tube. The overloaded (gate limited) part of the signal at the output looks just like the same as it is present at the grid itself.

    Some instruments like spector send a very strong level into a preamp input when the volume knob is turned to full open. An additional boost at the low end lets the level easily exceed the instruments full headroom reserve which is of several volts with a new battery.

    Whereas some grid overloading at transients is insignificant cause it is not audible, However to much of this "effect" will be clear audible as distortion.

    I have exactly the same problem with my USA spector and my 70's svt. The spector can easily overload the grid of the inital tube stage. I myself fix this problem very smple by turning down the level with the vol knob on the instrument!
    Last edited: Jan 27, 2015
    SteveCS likes this.
  18. TyBo


    Dec 12, 2014
    I have an old BlueTube preamp into which I substituted a NOS 12AT7 ... I made the change a long time ago, so I'm not quite certain, but I'm pretty sure its a Sylvania (not gonna open it up now to find out) . It definitely gives the unit a bigger sound, compared to the stock 12AX7. I recall subbing a bunch of different tubes to see what they'd do, and the regular, current 12AT7's did not give the same effect, did not give a particularly good sound. So YMMV, but the right tube can make an actual difference, as your research also indicates.
    Last edited: Jan 27, 2015
    therealbigsteve likes this.
  19. BurningSkies

    BurningSkies CRAZY BALDHEAD Supporting Member

    Feb 20, 2005
    Syracuse NY
    Endorsing artist: Dingwall Guitars
    I agree with this. The AU7 sounds better to me, although less gain. I like them better than AX7's. My favorite 'drop in' replacement for a 12AX7 is a 5751. It just 'sounds right' to me.
    therealbigsteve and B-string like this.
  20. Steve Dallman

    Steve Dallman Supporting Member

    The Blue Tube is a "starved plate" design running the tube at low voltage to decrease it's linearity and make it easy to distort. Changing to different tubes in this design is different than changing tubes in high voltage tube circuits.

    Thisbass, the gain of the tube affects sensitivity, so a lower gain tube will not distort as easily as a higher gain tube, given the same input signal.

    It's easy to demonstrate. In the PI slot of a Fender, a 12AT7 will stay cleaner and tighter longer than a 12AX7, with the same circuitry. Same thing in the first preamp slot. Lower the gain in the first stage, either by changing the ciruit (grid, plate or cathode resistance) or using a lower gain tube, and you increase headroom.
    therealbigsteve likes this.
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