Pulling Mesa Rectifier Tubes.

Discussion in 'The Workbench' started by charveldan, Jul 10, 2018.

  1. charveldan

    charveldan Well-Known Member

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    [​IMG]

    So i use the Hi-power SS Rec mode only. My heater voltage was a little low measured @ Obeid Khans house. He said it was no problem but that this amp should only run on Diode Rec.

    What [if any] are the downsides of pulling the 5U4 Rec tubes ?

    Im theorizing that if i do pull then there will be more heater voltage to go around.

    This amp has a new quad of EL-34 now. Bias is spot on.
     
  2. ampmadscientist

    ampmadscientist Well-Known Member

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    You can pull the rectifier tubes, these run on a 5 volt filament winding. Not the same as the other tubes.
    If you pull the rectifier tubes, it will still work I think regardless if it is set on solid state or tube rectifier.
    This is because the SS rectifier is always in the circuit no matter if it's set on SS or not.
    (surprise)
     
  3. charveldan

    charveldan Well-Known Member

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    http://diy-fever.com/wordpress/wp-content/uploads/2009/12/dual_rectifier.pdf

    Have a look at this schematic .... [scroll down]
     
  4. anitoli

    anitoli Well-Known Member

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    EL34's have a higher heater current draw than a 6L6GC type tube, it's normal.
     
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  5. mickeydg5

    mickeydg5 Well-Known Member VIP Member

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    How about this?
    Measure your filament voltage on the amplifying tubes with the rectifiers loaded.
    Then measure your filament voltage on the amplifying tubes with the rectifiers unloaded.
    Is there a difference?
    Decide.

    If unloading the 5V secondary provides more power to the other secondaries then good for you.

    Or your 6.3V secondary could be a little under tolerance.


    By the way what is the filament voltage on your amplifying tubes?
     
  6. charveldan

    charveldan Well-Known Member

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    Found this from the Boogie Board :

    "ALL pre and power amp tube heaters are connected to the same 6VAC tap on the power transformer. The pilot lamp is also supplied from this tap, so if the pilot lamp works (or if there is ~6VAC at the socket) the transformer is fine. After the pilot lamp comes the 6L6 heaters & preamp tubes V2-V5. If the 6L6 heaters work and V2-V5 do not it is tech time. Next comes a bridge rectifier to convert to DC voltage. This DC voltage supplies the heater for preamp tube V1 as well as the switching matrix."

    "The 5U4G(B) rectifier tubes have their own 5VAC heater tap from the PT."

    I measured the bias with & without the 5U4's and the bias is good either way, but i have just a tad more plate voltage without so for now i pulled them.
     
  7. mickeydg5

    mickeydg5 Well-Known Member VIP Member

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    You did not answer the riddles. What are the PT 6 volt secondary measurements with and without the 5U4's?

    I am interested in knowing.

    What did Obeid mean by low in this amplifier?
     
  8. charveldan

    charveldan Well-Known Member

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    Sorry bro i aint poking into hot sockets. Just for-get-a-bout-it.

    My heaters are fine.
     
  9. mickeydg5

    mickeydg5 Well-Known Member VIP Member

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    I forgot you have that fancy hands off bias probe for your amplifiers. :)

    Seriously though, all you have to do is measure across the pilot light. Its about 6VAC,
     
  10. charveldan

    charveldan Well-Known Member

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    Thats cool, i just don't wanna pull the chassis again, been doing since the weekend.
    Obeid said it was a little low but not a big deal. IDK where on the board he was measuring cuz i was across the room at that time.
     
  11. mickeydg5

    mickeydg5 Well-Known Member VIP Member

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    Maybe Obeid measured 5.9 or 6.0 and that is what I was wondering; if he considered that low.

    Oh well, maybe next time you pull the chassis.
     
    Last edited: Jul 10, 2018
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  12. charveldan

    charveldan Well-Known Member

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    This is what she's sounding like tonight with the 5U4's pulled & the new matched quad of Tungsol EL-34B's.
    Little chorus, verb & delay here & there in the new series loop.

    It was low volume w/a OCD pedal.
     
  13. mickeydg5

    mickeydg5 Well-Known Member VIP Member

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    It does sound mean. :headbanger:
     
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  14. ampmadscientist

    ampmadscientist Well-Known Member

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    If unloading the 5V secondary provides more power to the other secondaries then good for you.


    No it won't. The secondary for the 5V winding should be completely isolated from any other winding.
     
  15. ampmadscientist

    ampmadscientist Well-Known Member

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    Of course there is more plate voltage, the SS rectifier by itself is more efficient.
     
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  16. mickeydg5

    mickeydg5 Well-Known Member VIP Member

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    I am not calling you Ampmad any longer, just madscientist. Like pointed out in another thread it seems you always know everything yet you do not. You converse as if your word is absolute but it is not. You are more like a mad scientist.

    Yes the secondaries are isolated from other windings. I agree. Did everyone get that?
    The secondaries are also isolated from the primaries. So by your description there should be no voltage/current /power to the secondaries.
    Oh however they do get power. That is weird. No it is not because they are supposed to develop power.

    Transformers: power in equals power out
    The transformer is designed to transform from the primary a specified amount of power to each secondary circuit with tolerances.
    If one of those circuits is unloaded the power can be diffused to the remaining loaded circuits, not 100% but some of it. Nothing is perfect. Its not just possible, it is probable.

    I tested my 5AR4 just to see. It is a bit different in function and design from the Dual Rectifier but proves the point. The 6.3VAC filament had a 1/3% to 1/2% bump in voltage when pulling the rectifier tube. No that is not much at all. It is a 5VAC circuit made for a single 5AR4 which is 1.9A draw.
    Now lets look at a Dual Rectifier amplifier. It has two 5U4 at 3.0A each which total more than 3 times the current draw of the 5AR4. So there is reason to believe pulling these two tubes and unloading a good bit of power might make more of a difference in this scenario. It might be less than 1% but I still want to know and am interested.

    That is why I asked. That is why I want to know. I do not have a Dual Rectifier in front of me to test but CharvelDan does.
     
    Last edited: Jul 11, 2018
  17. charveldan

    charveldan Well-Known Member

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    I didn't know the spec's but i figure the amp draw plus the heat & wasted energy of the 5U4's just burning away plus the increase in plate voltage without them i might as well pull them as im not using them.
    Also i figure it may lighten the load on the Transformer a tad.

    In tube rec mode the wattage output was about 4 watts per tube. In SS diode rec the output is around 16 watts per tube. The amp sounds & feels way better in high power [SS] mode to me.

    Obeid as an Engineer & amp designer & I both agreed that some of the features on the DR were Marketing & "over-engineering."

    I would have much prefered a bias pot & series/parallel loop mini toggle compared to the "bold/spongy" & "Tube Rec" features.
     
    Last edited: Jul 11, 2018
  18. mickeydg5

    mickeydg5 Well-Known Member VIP Member

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    Exactly. (3A x 2) 5V = 30 watts.
     
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  19. ampmadscientist

    ampmadscientist Well-Known Member

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    Well it lightens the load on one winding, but not the others.
     

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