PRRI: caught off guard by measurements

Discussion in 'Amp Tech Center' started by Luthier Vandros, Aug 14, 2019 at 9:12 PM.

  1. Luthier Vandros

    Luthier Vandros Tele-Holic Silver Supporter

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    Yikes! I’m still relatively new to Fender’s RI amps and I have a 2013 PRRI on the old bench. With a NOS RCA 5AR4, the 6V6 plates are at 440v. With NOS GE 6V6’s, the ma’s are up to 38!

    I dropped a NOS 5V4 into the rectifier slot and got the plates down to 430v around 28ma. With the 5V4 and the old EH 6V6’s the plates are down to 420v @ 19ma.

    What a hostile environment for a 6v6! Anyone else have to wrestle these little RI’s into a more hospitable range?
     
  2. Luthier Vandros

    Luthier Vandros Tele-Holic Silver Supporter

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    Ol “new dad brain” has got me putting the cart before the horse. Found s plethora of info on these hot little numbers here. Pls delete.
     
  3. EddieLocrian

    EddieLocrian Tele-Afflicted

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    I like your user name btw, very funny.
     
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  4. Luthier Vandros

    Luthier Vandros Tele-Holic Silver Supporter

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    Ty!
     
  5. Luthier Vandros

    Luthier Vandros Tele-Holic Silver Supporter

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    Resolved with Tung-Sol Reissue 6v6’s. Didn’t even have to touch the bias circuit. VP back to 430; idle at 18.5 MA. Glorious sounding amp.
     
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  6. Wally

    Wally Telefied Ad Free Member

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    If that is where you like it, that 55% of max plate dissipation is good to go. I like it warmer. Ommv.
     
  7. Luthier Vandros

    Luthier Vandros Tele-Holic Silver Supporter

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    Strange the tube bias calculator puts that around 70%. So much for the late night tweaking.
     
  8. Wally

    Wally Telefied Ad Free Member

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    430 x .0185 = 7.96 watts - (.05 x 7.96) = 7.92/14 = 56.5%

    I use 14 watts as a max plate dissipation factor for almost any 6V6 except some ancient version, perhaps. If one uses 12 watts, then the dissipation factor would be 66%.
    At any rate, if it sounds good, play on.
     
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  9. Luthier Vandros

    Luthier Vandros Tele-Holic Silver Supporter

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    Your math makes sense. I was looking at 12w. I’ll play with it and see if I can detect any changes in tone.
     
  10. Luthier Vandros

    Luthier Vandros Tele-Holic Silver Supporter

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    Just saw the spec sheet for the tubes. Such a newb oversight. These tung-sol reissues are 12w’ers. My new dad brain hurts!
     
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