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Re: Power Calculations - No Clipping

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gusser

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In Reply to: Power Calculations - No Clipping posted by Satelliteman on September 17, 2006 at 15:06:26:

First where is the 550ma coming from? Do you mean 50ma? 500ma is a lot of current to pass through an audio tube.
You must mean Vsquare over R. I is the current. Other than that your calculations are correct 18vrms into 8 ohms is 40 watts. Is you meter reading true RMS at 1khz? Many lower cost meters are only accurate at 60hz. Try measuring the power at 60hz and compare. The amp should be reasonably flat between 60hz and 1khz.

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Re: Power Calculations - No Clipping - Satelliteman 16:04:39 09/19/06 (8)
Thankyou for that -
Yes , I mean V squared over R . I will check the Fluke DDM again - its pretty new , and at 60 hz as you say .
550 mA is the correct average setting of amplifiers output stage bank current ( for all tubes biased at Class A levels ) Its a value measured with inline ammeter . Its not specific for individual tubes , but a general average for 4 6AS7G tubes ( 8 triodes ) fully switched on . Correct me if im wrong someone - im applying my basic understanding of these amps here . Perhaps the term .." Collective Current " per bank would be appropriate .
Stu
- Re: collective current - Ralph 15:13:32 09/20/06 (7)
  is a good term.
  The bias has little effect on power, but does affect distortion. B+ voltage affects power output. The amp is speck'ed to make full power (60 watts) into 8 ohms with 120V in (if you are in the US). Generally we do a bit better than that- 65 to 67 watts is common.
  A common problem area is the power cord. It is best to run the test with a variac and measure the input AC voltage to make sure there is no sag at full output. Since the amp operates in the A2 window at full output, there can be significant voltage sag in the power cord and the like. It can rob the amp of significant power! If there ever was an argument for upscale power cords and their audibility, this is definately one.
  - Power cord ugrade - Satelliteman 19:51:20 09/21/06 (1)
    Although the current should be considered for the ratings of the powercords ...I can assure you that primary mains current on the toroids is approx 1/2 what is present in the US . We have 230 vac supply here , and I think its approx 240 in Australia . I think the secondary voltages ..esp the output stage supplies , are down slightly because the Toroids were wound with 240 primaries , instead of 230 vac . However - a plus to this is , that if I move to australia ...things will be fine ! - not stressed .
    Guys - Im fine with the TOTAL build outcome - really
    Stu
    - Re: Power cord ugrade - TUBEVIBB 07:02:13 09/22/06 (0)
      Trun transformers around primary as secdaire.Then v. be about on the money thanks T.V.
  - In the US - ...No , im in New Zealand . 230 - 240 VAC - Satelliteman 19:22:18 09/20/06 (4)
    Hi Ralph , I sent you a pic of both my of amps together on the dining room table .
    These are the voltages / references that I have measured in the amps are as follows
    Output stage supply is 135 VDC
    Driver Supply is +325 & -327 .
    Bias value reference is approx -50
    Pins 2 & 4 ( V4 ) is +292
    Pins 1 & 4 ( v2 ) is 46.9 , and Pins 3 & 6 ( v2 ) is 53.2
    Pins 3 & 6 ( V1 + 1.6
    Pins 6 ( v3 ) is -92.7 , Pin 4 ( v3 ) is -95
    Pins 1 ( v3 ) -226 & Pin 3 = -222
    Im not after more power , just wanting to confirm that I was measuring it correctly .
    My original post was to describe how I was doing it ( at 1khz ) biased at 500 mA ...and then measured V squared / R ...with the Scope & Fluke DDM . The scopes Peak to Peak reading was multiplied by 0.707 ....and the Fluke DDM is good for 100Khz ( so it says )
    I have a Fluke 734 02 series
    Cheers Stu
    New Zealand on 230 and up to 240 vac
    - Re: In the US - ...No , im in New Zealand . 230 - 240 VAC - Ralph 10:19:04 09/21/06 (0)
      Sounds to me like the B+ voltage is a little low. 140V is a better place to be. You could buck that up with a small auxilary transformer.
    - Re: In the US - ...No , im in New Zealand . 230 - 240 VAC - tubevibb 05:19:50 09/21/06 (2)
      What is output stag v without tubes.with 135v unloded 150v.Is it good to pull down transformers?thanks T.V.
      - output stage voltage - Satelliteman 00:06:30 09/24/06 (1)
        
        In Reply to: Re: In the US - ...No , im in New Zealand . 230 - 240 VAC posted by tubevibb on September 21, 2006 at 05:19:50:
        
        I have read youre request Tubevibb . What is youre output stages windings AC voltage ..measured at the input to the Bridge Rectifiers ?
        Stu
        
        Re: output stage voltage - tubevibb 06:21:30 09/24/06 (0)
        
        In Reply to: output stage voltage posted by Satelliteman on September 24, 2006 at 00:06:30:
        
        I have 105ac 110ac 120ac at bridge. After 130dc 140dc 150dc.TO RUN a/b 150dc bias up,I CAN GET MORE POWER.But not needed,but I do own ESL all so. thanks My transformers R 1kva per winding.

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