Tube rolling a 2 channel twenty head

Discussion in 'Amplifiers' started by cmedcoff, Jan 17, 2017.

  1. cmedcoff

    cmedcoff New Member

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    I only recently learned the term "tube rolling"...

    I've recently purchase a 2 channel custom 20. I'm looking for a more compressed, more Marshall type of tone. (Please don't tell me to buy a Marshall I've owned and tried many but they have their downsides). I'm hoping that changing, if possible, the 5581's in the 2-channel 20 to EL34 which I'm guessing greatly contributes to that more Marshall type of tone?

    I like the 2-channel custom for it's feature set, the fact that it comes in a head (otherwise I might have bought an Archon), it's wattage, weight, etc.

    1) is this possible?
    2) what is the level of effort e.g. any modifications required

    Can anyone point me in the right direction? Links, etc.

    Thanks.
     
  2. AP515

    AP515 Mostly Normal

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    First of all, you may know more about this than I do. I'm still learning this stuff too.

    Ok, as I understand the 5881, the footprint is the same so you can put in the EL34. It will go in the socket. But biasing must be done. I don't know what the 5881 takes for a bias value, but the EL34's are biased at about 30mV (given that the voltage is really across a 1 ohm resistor). I have swapped EL34's in place of 6L6's in a custom 50 and the rebias is pretty simple since PRS put the terminals and the pot in, very conveniently, at the back of the amp. I don't know if the Custom 20 is the same but one would think they are similar.
     
  3. cmedcoff

    cmedcoff New Member

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    Thanks. I've also read somewhere that the EL34's draw more filament current so I guess I'd need to know that the transformer tap for the filament supply can handle that? Anyone have any insight?
     
  4. Mr_You

    Mr_You New Member

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    I would start with preamp tubes first and move into power tubes later.

    EL34s will change the voicing of the power amp slightly (more mid-range), but not affect the voicing of the preamp. You'll need to swap preamp tubes to affect the high gain voicing of the amp. And there is really only so much you can do without heavily modifying the amp.

    Take a look at this PRS SE20 overhaul page. I don't know what preamp tubes the Custom 20 comes with, but if it has a JJ 12AX7 then swapping in a TungSol 12AX7 might tone down the crunch a bit to your liking. You'll have to do a bit of research to find out which tubes you want to try and how the order of the tubes used for the channel you've selected affect the end result. For example, using a 12AT7 or 5751 in front of a 12AX7 reduces the amount of signal going into the 12AX7 which can result in lowering the resulting gain/distorted tone giving a more vintage high-gain tone.

    If you switch from 5881s to EL34s then you may or may not need to modify the amp, but I believe you'll have to use a higher or lower ohm jack? IIRC there will be an ohm mismatch. You'll want to confirm.
     
    #4 Mr_You, Jan 18, 2017
    Last edited: Jan 18, 2017
  5. cmedcoff

    cmedcoff New Member

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    Thanks, this is helpful. The 2-channel custom actually has 12AX7's in the pre-amp which is actually the right tube from a "Marshall" type of tone. My goal isn't to reduce gain but rather get more compression and more mid-range, less boomy bottom - I run the dirt channel with bass on 0 and it's still lots of bottom end. It's almost ironic that I have this "problem" now as my previous amp was a Marshall JVM410 and for my tastes it was way to heavy (I had the combo), not enough bottom end (unless you turned in up to a ridiculous volume). It had all the compression and mid-range I wanted needed. Just want to get some of that back with this amp.

    I've not opened up the amp. Does anyone know what brand of 12AX7's come in this amp. Perhaps a swap of the pre-amp tubes for same type of different make might help. Also good point about a possible difference in the output impedance of the EL34's and how that may or may not work with the existing circuitry and output transformer. I though I might run into someone here that's had first had experience with this on this particular amp.
     
  6. AP515

    AP515 Mostly Normal

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    I believe they are JJ's. They were JJ's in my 50 and the "H". The website also says the bias is adjustable so I bet the transformer can handle the El34's. My 50 did just fine, but I wonder if you put two in will you be pulling 50 watts like mine?

    From the website:
    Watts 20 Watts
    Channels Lead/Clean
    Power Tubes (2) 5881
    Preamp Tubes (3) 12AX7, (2) 12AT7, (1) 12DW7
    Output Jack Configuration (2) Parallel Jacks - 4,8,16 Ohms
    Fixed/Adjustable or Cathode Bias Fixed Bias (Adjustable)
     
  7. cmedcoff

    cmedcoff New Member

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    Hmmm more good points/questions. The 12AT7 and 12DW7 I understand to be just lower gain versions of the 12AX7. I'm guessing those are used on the clean channel?

    So even if the circuit/output transformer can handle the output impedance of the EL34's, can it handle the current aka the power. Not sure. I know my 2x12 cab can handle it. it's a DV Mark and handles 300 watts.
     
  8. AP515

    AP515 Mostly Normal

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    Yes, I'm going by memory so these are probably just in the ball park, but:

    12AX7 gain ~ 100
    12AT7 gain ~ 70
    12DW7 gain ~ 20

    They are not on any channel. They run other functions. The preamp as three 12AX7's. It's the same preamp for the clean or the dirty channel. The other 3 lower gain tubes run the reverb, the phase inverter, and the FX loop.
     
  9. BeerBatteredPhish

    BeerBatteredPhish New Member

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    More midrange you say, try a Mullard reissue 12AX7 or a Sovtek 12AX7LP. (Long plate). I find the long plate tubes produce a richer mid range and reduce some of the top and bottom extremes.
     
  10. LSchefman

    LSchefman Hears Tones

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    In my experience, the type of output tube (for example, EL34 vs 6L6) is a relatively small component of what gives an amp its overall character and tonal balance.

    A lot has to do with the tone stack; a lot has to do with the transformer; a lot has to do with how the preamp tubes overdrive with input applied; there are different circuits, different capacitors, and on and on endlessly, that create what we perceive of an amp's tone.

    Can tubes make a difference? Sure, but it's not as large as you'd imagine.

    On the other hand, I've improved the tightness of the bass of my HXDA by changing to NOS Siemens tubes, but it's subtle of course.

    In any case, you're not going to change your amp into a Marshall merely by swapping the output tube types. I more effective suggestion would be something as simple as a graphic EQ pedal. You might want to try one in front of the amp, but also try it in the effects loop.

    I think what you'll find if you test out this concept is that the tone shaping you can get this way will far exceed what you can accomplish by means of a tube swap.
     
  11. The Fight

    The Fight Long Hair Demigod

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    My Marshall will always sound likes Marshall and I'm OK with that. But for me personally, I've noticed that sure tubes change the sound but it's subtle like Les said. What I notice the most is how "feel" of the amp changes, as that to me can be the big difference.
     
  12. DreamTheaterRules

    DreamTheaterRules New Member

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    What speakers/ cab are you using with the C20?
     
  13. cmedcoff

    cmedcoff New Member

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    I'm using DV Mark Neoclassic - its open back. I've also used with a friends B-52 4x12 which is closed back. No significantt difference to my ear.

    The other night at practice I starting to use the EQ on my G-Major to roll off some bottom end. I noticed that when I began to cut bottom end by anywhere from -6 to -12 db around 1KHz that I began to hear a more mid-range type of tone that I associate to more of a marshal type of sound. Again it's not the amount of gain, I like lots of it, its more about more midrange (but with some bottom) and more compression. The C20 has lots of gain but never really feels like it get's very compressed like a Marshall and as I've said before too much bass.
     
  14. squirrel211

    squirrel211 New Member

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    Just as something else to consider, different rooms can affect the amount of bass pretty drastically. I play shows at dock bars, where I run the bass on my amp at 6; and there are 2 venues where I need to run the bass at 1.

    Speakers can be a huge factor for EQ response. An M mag speaker is going to be richer in the mids, and thinner in the bass, than an H mag. I'm not familiar with Neo's, but I know that changing speakers in my M-styled amp changed the character a ton.

    Also which pickups are in your guitar? I've noticed that my 57/08's are rather uncompressed when compared with the Suhr Aldrich I have in the bridge of my 20th Anny SE Cu24. If you like a lot of gain, maybe check out PRS's other pickups? Maybe the \M/? <-- that should add mids and reduce the bass response slightly too.

    Finally, where is your volume set when you're looking for compression? If your master is low, you could get an attenuator (for this application/since you're playing live in a band, I'd recommend a Tone King Ironman Mini, due to it's ability to give you a solo boost) and turn the master up higher. The amount of compression increases with attenuation, so you could turn your amp up louder, and increase the attenuation until the compression characteristic was ideal.
     
  15. cmedcoff

    cmedcoff New Member

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    You make some good points here. At band practice my 2x12 cab is backed up into a corner and last week I thought of this and pulled it out and away. That did help some and this week I plan on moving to the other side of the kit to avoid the corner altogether.

    Hmmm speakers. I'm using the DV Mark's because of the light weight of the magnet technology called "neodymium" and I'd like to keep it that way. Here's a comparsion/debate if anyone care's to see. I've heard more speaker manufacturers are coming out with these and I guess I can look around to see what's available.

    I'm using fender noiseless in a PRS EG2. The amps sounds great with these. I've got Seymor Duncan Pearly Gates (suppose to be brighter right) in a PRS Torero, Seymour Duncan 59's in a PRS Custom 24, and stock in a PRS Zack Meyer.

    I probably get the most mids from the 24 and the Zack which seem to be really hot pickups, but the Zack sounds almost muddy (though it sounds awesome through my 1 watt Blackstar, my practice amp).

    Volume on the amp? I run the volume just about 12 o'clock at practice, maybe slightly less/more. This is enough to keep up the my hard hitting drummer and bass player. I would think this would be enough to drive the power amp a bit since its only 20 watts. Certainly interested in other's experience.
     
  16. squirrel211

    squirrel211 New Member

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    For this point in particular, an attenuator will introduce its own compression phenomenon. My suggestion would be to make the amp louder, and add an attenuator if you were looking for additional, non-pedal-styled compression. Since you use this amp live, I recommended the Ironman Mini because it is a pedal, with the SOLO function. The downside of using attenuators live is that solo boosts are largely ineffectual because of the compression the attenuator introduces; the Ironman Mini solved that problem with aplomb for me!!
     

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