4 watt power building

Discussion in 'The Workbench' started by zebrarock, Feb 24, 2020.

  1. zebrarock

    zebrarock Member

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    I would add last measurement i made with oscilloscope two days ago and it gave me a 15 volt signal peak to peak... applying formulas that ampmad posted it would give 3.5 watt rms output...significantly different, hence which method is most reliable ?
     
  2. ampmadscientist

    ampmadscientist Well-Known Member

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    What is the RMS measured AC voltage across the load?
    Plug sine wave into amp, Set sine wave for 300 KHz.
    Raise volume of amp until clipping occurs, then reduce the volume slightly until clipping stops.
    Using the Volt Meter: Now what is the AC voltage measured across the 8 ohm load resistor?

    Qual è la tensione CA misurata RMS attraverso il carico? Collega l'onda sinusoidale all'amplificatore, imposta l'onda sinusoidale per 300 KHz. Aumenta il volume dell'amplificatore fino a quando si verifica il clipping, quindi riduci leggermente il volume fino a quando non si interrompe. Uso del voltmetro: ora qual è la tensione CA misurata attraverso la resistenza di carico da 8 ohm?
     
  3. zebrarock

    zebrarock Member

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    4.2 volt ac.
     
  4. zebrarock

    zebrarock Member

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    This test will be the next...
     
  5. zebrarock

    zebrarock Member

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    Mickey, what sheet indicates as Veff , what exactly mean ?
    Eff...ective?
     
  6. ampmadscientist

    ampmadscientist Well-Known Member

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    15 volt signal peak to peak

    = 7.5 volts peak
    = 5.0325 VRMS into the 8 ohm load

    5.3025 V / 8 ohms = .6628125 A

    .6628125 A X 5.3025 V = 3.51456328125 "watts" RMS
     
  7. ampmadscientist

    ampmadscientist Well-Known Member

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    You are supposed to be getting 4 watts?
    And the actual watts is 3.5?
    You are not very far off.
     
    thetragichero likes this.
  8. zebrarock

    zebrarock Member

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    Yes it is, i realized that when i got peaks explained from this topic...hence the best way for measurement is by scope ? Or by a very good quality multimeter ?
     
  9. ampmadscientist

    ampmadscientist Well-Known Member

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    You could use either one but the scope tells you that there's no clipping in the output.
     
  10. mickeydg5

    mickeydg5 Well-Known Member

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    RMS, or root mean square (also called effective), voltage

    You need 12 volts RMS at the power tube control grids.
     
  11. mickeydg5

    mickeydg5 Well-Known Member

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    RMS, or root mean square (also called effective), voltage

    You need 12 volts RMS at the power tube control grids.
     
  12. mickeydg5

    mickeydg5 Well-Known Member

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    And I would at least measure at about 200Hz, the median for male and female vocal frequencies.
     
  13. zebrarock

    zebrarock Member

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    Ok , another thing i missed, now it is clear what effective means... hence since i get only 8.9 v ac rms before clipping could it mean i have a too warm bias ? Now i am measuring 13.4 v dc grid to cathode bias...
     
  14. mickeydg5

    mickeydg5 Well-Known Member

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    Are you measuring power output with an oscilloscope?

    And it is clipping because the Philips specifications state distortion tot = 3.2% at 4W.

    Where do you guys get "before clipping" when doing this?
     
  15. zebrarock

    zebrarock Member

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    On a perfect sine wave limit before clipping occurs...
     
  16. mickeydg5

    mickeydg5 Well-Known Member

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    You did not answer either of my questions.

    ...and your statement is wrong if you did not catch my drift. You are not looking for a perfect sine wave.
     
  17. zebrarock

    zebrarock Member

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    Yes, i check 1 khz signal across 8 ohm dummy load and turn up volume until perfect sineware exist, then i get value of ac volt from my multimeter and it is always from 4.2 to 4.5 ac volt rms.
    Once i did the same but getting peak to peak ac volt value from scope which gave me around 15 volt ac
     
  18. Timbo

    Timbo Active Member

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    Hey mate, The EL91 is mighty little valve.
    I built this....
    http://www.marshallforum.com/threads/10w-sol-clone.107080/
    To get the most out of them, I think a fixed bias supply is the way to go.
    What is your preamp/phase inverter going to be?
    The little buggers don't like to be HAMMERED.
     
  19. zebrarock

    zebrarock Member

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    For the preamp i used one 12AX7 with attenuator after second gain stage, first cathode is a 2.7 resistor bypassed with 1uF cap and the second is 820 ohm unbypassed res, both plates have classic 100 k resistor.
    I used cathodyne PI with a 6C4 tube (single triode) to get a non amplified clean signal to the grid of the power tubes. Everything works fine and the sound is great for me, but probably i did something wrong because cannot get 4 watts output power...
    Yes, fixed bias is better on this way, but could be a future upgrade, for the moment i have to know why or what i did wrong to get lower power i did not expect

    I know your project, i posted some comment yesterday on your article web page...(Matteo)
     
  20. zebrarock

    zebrarock Member

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    Mickey, did I answer your question in any way? If not please, let me know better, i would like to learn ever something more...
     
    Last edited: Feb 25, 2020

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