EL34, 6L6, 6V6 power amp section only?

Discussion in 'Building the Classics' started by dibble, Dec 5, 2019.

  1. dibble

    dibble New Member

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    I've always wanted to built an amp for myself. But, in the past couple of years I've moved over to amp modelers and profilers. IMO the preamp sections are quite well reproduced in software with today's state of the art.

    However, (IMHO) the poweramp section, FRFR and speaker modeling is still a ways off when you are after that in-the-room-with-an-amp sound. For a while, I've been plugging my preamp modeler in to the return of my EL34, 6L6 and 6V6 amps, and then in to an appropriate cab for what I consider to be dead-on "real amp" sound that I could never get with several FRFR attempts.

    The problem with this approach is while I can still get a ton more preamp options, I still have 3 amps and multiple cabs to deal with. Then I had an idea for my first build--build a multi-tube poweramp section (and later a cab with multiple speakers for different amp sounds). But, it may be too ambitious. So, I thought I'd ask here first.

    Hughes & Kettner already makes an EL34 and 6L6 amp. It's $3K. And, I'm not interested in their preamp section anyway. How tricky would it be to build just the power section of an amp like that--more importanly--on a $1000 budget? I was under the initial impression that I'd essentially be building 3 separate amps in one box (for my EL34, 6L6, and 6V6 idea) which would essentially triple the price of just building one poweramp section. I don't have the schematic, but I assume H&K have somehow used the same transformers and shared a lot of the same circuitry to get their 2-amps in a box. If so, then a 3-in-a-box would be > cost of 1 poweramp but <3.

    So, my question:

    Is it possible (worth attempting--worth the effort--sensible for a first build???) to build 3 power amp sections: one for EL34 (2), 6L6 (2) and 6V6 (2) sharing the same box and a lot of the same hardware? Ideally, I'd just like to flip a switch on the front to toggle between the 3 sections. If this pans out, then the next plan is to build a 4x12 cab with two Eminence speakers and two Celestion speakers so I can go 2x2 depending on which tubes/preamp I'm using.

    I'm sure I'll have a lot more questions. No, I'm not asking for a schematic or how to. I have a lot more research to do on the subject (and equipment to buy). I just wanted to know from the builders if this is a silly pursuit I should abandon now, or if it is possible and I should continue.
     
  2. neikeel

    neikeel Well-Known Member

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    :hmm: interesting idea. Might be easier with three single ended amps in one chassis, depending on how much output you want?
     
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  3. Im247frogs

    Im247frogs Well-Known Member

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    This makes me wonder if people will ever start building "classic" modelling amps from kits sometime in the future.
     
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  4. Adieu

    Adieu Well-Known Member

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    There were some cheapie self-biasing, tube-monitoring, mix-and-match-whatever-fits "Infinium" models from Bugera

    ....although that's not exactly what you asked for (cheaper, though).

    You could also probably jury-rig some togglable additional power tube sockets to work with that.

    Or maybe an inner pair/outer pair toggle mod for half-wattage operation without any tube swapping?
     
    solarburnDSL50 likes this.
  5. MickeyJ

    MickeyJ Active Member

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    The problem with this idea is the same problem that amp makers that claim to make amps with different ' voices' have.
    An amp maker can claim whatever he likes, but unless he has three different power supplies for the 3 different output tube types ( lets pretend fender is claiming to have made such an amp) then there wont be three voices at all, there will be one voice that sounds slightly different with each power tube type.
    An amp with truly three different voices , with one voice per each output tube type would need 3 power transformers. Note that if the amp had one power transformer with three different secondary taps, it would still use the same primary winding.
    What this means ( if using the same power transformer with three secondary taps) is the power supply for the three different output tube types has the same ' push' ( it's actually pull).
    The power transformers ' power' is critical in tone generation and amp ' punch'.
    now, we move onto rectification and filtration.
    Different rectifiers, half wave, full wave etc have different ' sounds' . Does the hypothetical fender amp have three different forms of rectification? if the amp wants to have three voices, it should.
    Same as filtration, will this fender amp have 3 banks of 1st stage filter caps all different sizes? Because that's what it will take to get 3 different voices for the three output tube types.
    Of course for a three voiced amp you'd need three output transformers as the output transformer is responsible for a hefty chunk of the tone generation.
    As I've said or inferred in the first sentence, amp makers who tried to convince us that by having three different pre-amps in the same amp they have an amp with three voices is patently untrue.
    All commercially available Multi-channel amps are simply 3 or four variations on the same theme, 3 or 4 pre-amp configurations for the same power stage, some with a very misleading ' rectifier' option.
    There are more variations in tone/punch to be had by having an amp with three truly independent power supplies ( and one pre-amp), but it would weigh, well, maybe 140 pounds and be twice as wide or deep as a Marshall Major.
    Realistically, a reasonable experiment considering the weight handicap would be a 2 power transformer amp with 2 different 1st stage cap networks, maybe a tube rec with the diode bypass with an optional full wave bridge rectifier, 2xel34 + 2x t66 , then you'd need 2 output transformers and of course your normal ( one or two separate )pre-amps and components.
     
  6. South Park

    South Park Well-Known Member

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    You have a lot learn about tubes
     
  7. ibmorjamn

    ibmorjamn Well-Known Member

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    Wow great suggestions ! Explain this rig in detail .
     
  8. ibmorjamn

    ibmorjamn Well-Known Member

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    Check in to the Mesa Rectifiers . It is more likely 6L6 or EL34 each style of tube has voltage required and power supply to match that . Lots of folks here know more detail but I would start off simple .
     
  9. neikeel

    neikeel Well-Known Member

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    You have just explained all the background to my post number 2 above!!
    With SE set up you can have different power supplies (rectifiers valve vs ss) virtual variac, with one PT and multiple options.
    Personally I think the differences between output tube tones is much more due to how the whole amp interacts, pre- and power together and the speakers, but with a modelled front end having a valve output section would still be interesting.
     
  10. MickeyJ

    MickeyJ Active Member

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    each style tube has it's own bias voltage requirement, same power supply otherwise, exactly the same, I suggest you completely avoid Mesa designs. You're going into new territory.
     
  11. dibble

    dibble New Member

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    Sorry to abandon my own thread. Holiday season, kids school, getting sick, guitar practice...life gets in the way. Anyway, thanks a lot to all of you, especially MickeyJ's input. That's well thought out.

    It all makes perfect sense. But, I still want to make an amp. should be a good project to start the new decade.

    So, change of direction.

    I have a marshall 40c that sounds amazingly like a JCM800 2203 when I put a 2203 model in to the return and crank it up.
    I have a fender super 60 1x12 (6L6s) that sounds amazingly like a twin, or a vibrolux when I input those models in to the return and crank it up.
    I have a Laney aor20 1x12 (6V6s) that sounds a lot like a deluxe reverb in the return.

    Now, I'm not suggesting I gut these amps. I've grown too attached to them to do that to them.

    But, how much of each amp would I have to re-create if all I want is to replicate the power section? I can follow the schematics out there to easily replicate a design. But, lopping of a whole section? I'm not sure where to cut.

    And, yes I guess my plan now is to triple stack three different power amps in a combo cabinet :-D
     
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  12. MickeyJ

    MickeyJ Active Member

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    I think, when using the return jack, that you're going straight to the little input cap just before the phase inverter tube ( attached to one of the grids) , maybe via some sort of pot/control for level.
    If you're getting the sounds you want to hear by using these return jacks, then if you want to make this amp, which I think is a really cool idea( put it on castors and roll it around the house) you just chop the amp at that point, that's most of the amp, all you're bypassing is the pre-amp tubes and pre-amp circuitry.
    You chop all the transformers, all the filter caps ( make sure you replicate the pre-amp filter cap value accurately, that's a big ' tone point' right there.) All the tube sockets including phase inverter but excluding other pre-amp tubes.
    It's easier than it sounds, just find that input cap to the phase inverter, again, it may have a level pot there somewhere, and chop it there.
    This is a great project, original, I like it.
    Use quality parts all the way through, it will be much better, proper high quality sockets, good wire etc.
     
  13. dibble

    dibble New Member

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    That was going to be the idea originally. But, filling up a little combo 1x12 cab with 3 amps won't leave much room for a speaker--unless It's possible to stack them end to end...hrm

    Not to mention that the respective speakers of each type of amp is a huge chunk of the tone. So, while I'm still thrilled with the idea of a 3-in-1 poweramp in a 1x12 enclosure, I think I'm going to need to fill a 4x12 cab with different speakers and some bank switching on it. Ultimately it looks like I'll end up with a tall half-stack with a lot of tone options.
     
  14. Matt_Krush

    Matt_Krush Well-Known Member

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    so...just a little results from an amp I built...
    a very modded 2204 with much more distortion and a power section to use most all the Octal tubes.
    EL34, Kt77, 6CA7 (group 1), 6L6, 5881 (group 2), 6550 (group 3).
    I can fully bias each group to their 70% (or more) range.

    For tone...(drum roll)...

    No significant difference going from one group to the other.
    Example: Tung sol EL34 to Tung Sol 6L6...very subtle difference. Different family group.
    I hear a larger difference going from say JJEL34 to Tung Sol EL34 or going from JJEL34 to JJKT77. These are all of the same family or group.

    When I built the amp, it was to see what I could get with the ability to switch different tube groups to coax different sounds AND so I use could use whatever I had available if needed.

    Now, everyone has their brand they like/dislike.
    I have found:
    I like Electro Harmonix 6L6s, Neutral on the 12AX7s, and detest their 6CA7s.
    Like JJKT77s, Like the 12AX7s (for marshalls...not other amps), Really like the ECC803, hate their EL34's
    Like the Tung Sol EL34, 6L6s, EL84, like the 12AX7
    Like the Sovtek 12AX7LPS, 5881, dislike all their other 12AX7s

    For Marshalls I gravitate to a mix of:
    JJ12AX7, ECC803 or Sovtek LPS, Tung Sol, and a China in the preamp...once in a while I may stick in an old RCA or Sylvania (if the tone change is positive in a significant way).
    For Power-amp: Mostly JJKT77 and TungSol EL34.
    China branded stuff....like only the high cathode voltage rating for 12AX7

    Many Brands and types out there, haven't and probably won't try them all as I have found consistent results I like.
     
  15. jensvonbustenskjol

    jensvonbustenskjol Active Member

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  16. guzzis3

    guzzis3 Active Member

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    To answer your origional question it's not hard nor need be expensive. If you want to get bogged down in tiny variations then the stuff about power supplies and transformers starts to matter but for your FIRST amp build you need to keep things simple. You don't need to omit the preamp you just need to keep that stage clean.

    IMO start with an X86 p1 extreme:

    https://ax84.com/archive/ax84.com/p1x.html

    When you build it start by making the power supply and get it to work, then build the rest. Put a signal in and make sure you have output at the preamp out then get the output stage going. VR3 to R8. Actually ditch all that. Take the horizontal line from R18/the output of V4A and join it straight to R8, you don't want that preamp section. R10, C7/8/9 and those pots scrap all that.

    If you overspec the power section you can wire as many valves in parallel as you want and switch between them at the preamp out (before R8). I would use a really good switch or switches, you are dealing with big voltages. Usual warnings about the dangers of high voltages etc.... I would set up self bias for the output valve/s and no negative feedback. That will give you more valve "feel" but with a low gain preamp distortion won't be overwhelming.

    So now you have a class A single ended amp with one big power tranny and several small output trannies sharing a fairly clean preamp. I assume you want to get your distortion mostly from your modeler.

    Now you have your first amp project working you can move on to more complex cork sniffing designs. Should be a fairly cheap quick project. Next get a 4x12 cab and stick in 4 different speaker and a switch between them.

    2c.
     

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