Single Ended Output Build

Discussion in 'Building the Classics' started by RickyLee, Jan 15, 2018.

  1. danfrank

    danfrank Well-Known Member

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    HaHa!
    There is a difference to the sound of each.
     
  2. RickyLee

    RickyLee Well-Known Member VIP Member

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    Yeah, was thinking about something along the lines of having something to do to keep busy and maybe a bit of income for when I retire as well.

    I will keep you guys posted. I am thinking I am going to go with that Classic Tone for now. Might have to wait till end of month to put my order in for the transformers.
     
  3. RickyLee

    RickyLee Well-Known Member VIP Member

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    Sounds good. What model output transformer is that and what power tube(s)?
     
  4. ibmorjamn

    ibmorjamn Well-Known Member

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    russian 6p1p 10w musical power supply on ebay , it has a marshall jcm 800 style pre amp circuit. I have not played it in a a while .
    I also have a epiphone valve jr that I modified , it's pretty good but those little 5w amps are fairly loud in a small room.
     
    Last edited: Feb 2, 2018
  5. johan.b

    johan.b Well-Known Member

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    Not trying to highjack the thread...but i thought I'd share and see If anyone has objections. ..and offering a place to start. .

    Since my moost current rig is a floor based 2203 preamp that i run into whatever power amp/speaker available, i could use a small power amp for home playing...and as stated earlier. .now i need to know...
    Here is a tiny poweramp i drew up. Fixed bias. Fender reverb transformer. Adjustable nfb, a watt or two. 12ax7 input, 12at7 output tube.
    Elevated ground for output cathodes, for easy bias arrangement
    1516641447979-1850524628.jpg

    What do you think?
    J
     
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  6. danfrank

    danfrank Well-Known Member

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    Looks interesting! I've never used dual triodes as output tubes before so I don't know much about such circuits.
    I was originally thinking a Champ like circuit (6V6) but with fixed bias. Pleximaster has been working on something like this and he put a switch in the circuit so he can switch between fixed and cathode bias. Take a look:

    http://www.marshallforum.com/threads/holiday-vintage-marshall-builds.99193/
     
  7. RickyLee

    RickyLee Well-Known Member VIP Member

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    I have no experience with those low watt triode power stages. But it looks interesting for sure. I have two output xfmrs on this project I am messing with now. The small OT is running two EL84's push pull cathode bias. I might just have to try out your circuit later on this one . . . .
     
  8. johan.b

    johan.b Well-Known Member

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    Cool. Please note thought that most leds are specified. Max 30mA of somewhere near that. So two 12at7 is about the limit of what they can take, using it as elevated ground.
    If you use a more powerful tube, you'll need something else, and probably higher voltage drop..
    J
     
    Last edited: Jan 24, 2018
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  9. jensvonbustenskjol

    jensvonbustenskjol Active Member

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    I have to add something with regards to single ended amps:
    One of my favorite amp is Fargen mini plex. It's a 12W SE amp with dual el34.

    I've really want to try build something with that kind of stage. I've been constantly thinking of this since you started this thread

    Thank you for that ;)
     
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  10. ibmorjamn

    ibmorjamn Well-Known Member

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    http://i.imgur.com/ee7bOhn.png
    The output Transmformer is a Musical Power Supply
    OT10SE USA on eBay. USA made.
    This is good for the 6P1P russian tube in the schematic.
     
  11. tschrama

    tschrama Active Member

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    5K primairy for a parrallel 12AT7 @ 300V?
     
  12. ibmorjamn

    ibmorjamn Well-Known Member

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    If it is dual El34 they are running Parralell I believe. From a guy on his page dvnator chasing tone.com
    http://chasingtone.com/dvnator/wp-content/uploads/sites/6/2017/11/SEPlex_v2.jpg
     
  13. ibmorjamn

    ibmorjamn Well-Known Member

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    http://www.edcorusa.com/xpwr021
    Power transformer for a 120V, 60Hz. line to 290V at 250mA and 6.3V (3.15-0-3.15) at 4A center tapped
    EL34 has a good current draw hence 250mA
     
  14. ampmadscientist

    ampmadscientist Well-Known Member

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    Did you get that B+ up to 680 Volts yet?

    Edcor is cool, because they will build you anything just about.
    My next project will be a Circlotron, which I always wanted to try for guitar amps.
    (the primary of the OT is cathode driven) The CT of the OT primary is ground.
    And I will need the special transformer, which I think Edcor will wind.
    upload_2018-2-4_17-3-48.png

    Did you know that a Circlotron requires 5 separate power supplies?
    That's where you get an Edcor PT built.
     
  15. RickyLee

    RickyLee Well-Known Member VIP Member

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    Never heard of the Circlotron. What type of sound do you get out of that power amp compared to a Marshall 2204 type?

    Was your question of me getting 680V B+ a typo? Was wondering what you were referring to there?

    I have not ordered my transformers yet. I am messing with a project that was a Princeton Reverb type circuit that I converted to a 2204 preamp into a cathodyne phase inverter. I am using 56K/56K for the plate and cathode on that cothodyne PI. Not too impressed with it at his point.
     
  16. johan.b

    johan.b Well-Known Member

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    Well. My test build is coming together. Not pretty in any way. Just a lot of reused parts. And not safe outside my mancave.. .underfiltered.so Some hum and a little intermodulation. But it works..have to wait a few hours to see how it distorts. .that's after all why i did this. .only change from schematic above is the LEDs are replaced with a string of 6 1n4841. They are good for 500mA. But only drops~0.7volt. B+ is 280 volt. Bias set to -3 volt against cathode for 10mA/ side. From darasheet curves. Will check with oscilloscope when i get a chance
    1518344547537-265451543.jpg
    1518344635314218715287.jpg
     
    Last edited: Feb 11, 2018
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  17. johan.b

    johan.b Well-Known Member

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    ok, danfrank was right...fixed bias makes single ended behave and sound much more like push/pull. at least the one above. :)...I guess I have to call it "BigBoy"
    NFB at halfway, clipping start occuring at 200mV input.
    i changed the bias to just four 1N4148( it gave 2,96volt) and grid resistor straight to ground.
    being just a power amp, the sound is rather flat and boring, pushed with boss GE7, with the mids scoped, gave a very convincing fender amp type sound. I'm sure I can use it for home practice with my floor preamp. I did forget to measure output power, but I'm guessing around 0,5watt. run into overdrive, it was plenty loud for a small mancave but still tollerable for the family watching TV upstairs..my Marshall 1watt DSL is louder...fun little experiment/project...now what...
    J
     
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  18. ampmadscientist

    ampmadscientist Well-Known Member

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    A circlotron (not cyclotron) has never been tried with a guitar amp. (as far as I know)
    We don't know the results.
    But what we are doing here, is to develop a new signature sound, which is a departure from what everybody else is doing.

    680 volts is what I imagined for a single ended amp, that is loud enough to go head to head with a push pull amp.
    Single ended is much less efficient compared to push pull. Probably: less than 1/2 as efficient.

    See:
    you think of wattage as being a measuring stick that determines "how loud" and amplifier is...
    But what I have said many times is: that's not an effective way to judge loudness.
    It's more of: what speakers?
    It's more of: what distortion?
    It's more of: compression?
    It's more of: power supply voltage.
    that really makes an amp loud(er).
     
    Last edited: Feb 12, 2018
  19. mickeydg5

    mickeydg5 Well-Known Member VIP Member

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    There are or were OTL's but I do not know of any used for musical amplification. You usually have to have a shit load of output tubes to get the output impedance low.

    $20+ at 8, 12 or 16 tubes is expensive especially if you burn them up regularly.
     
  20. RickyLee

    RickyLee Well-Known Member VIP Member

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    200mV signal was going into the input of the power amp? Would be equivalent to having 200mV audio signal going into the 22nF cap of a Marshall phase splitter input? The 22nF cap between tone stack and phase splitter? That is not much signal at all. My bridge humbucker hits peaks of well over 500mV.
     

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