PRRI and JJs... how to rebias

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by Webfoot, Jan 18, 2015.

  1. Webfoot

    Webfoot Supporting Member

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    Was thinking of putting in JJ 6V6s in a PRRI and was thinking I would need to rebias. Have rebiased a DRRI with the screw adjust thingy and a Euro tube socket with DVM. But is there a bias adjust for a PRRI and can it handle JJs?
     
  2. Blue Strat

    Blue Strat Member

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    JJ's shouldn't be an issue other than they don't sound like 6V6s. Not sure if there's a bias pot in that amp or not. The original PRs did not have a pot.
     
  3. spayne99

    spayne99 Member

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    PRRI has a bias pot. It's between the transformer and front panel. You'll probably have to pull the chassis a bit out to access it fully because it's partially obstructed by a strip of wood on the cabinet.
     
  4. Ken Zuercher

    Ken Zuercher Member

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    Mike, I use JJs 6V6s a lot and like them a lot. I looked throughout he slot in the plate and they look like beam power tubes as the grids look lined up inside. My understanding is that the original 6V6s were not beam power tubes. Am I correct about being Beam Power tubes? I have a number of older used 6V6s and they sound different than the JJs. The point of this is they might be baby 6L6s with a bit less edge to them to my ear.
    Ken
    I make amps for sale
    Zuercher Amplification
     
  5. Laurent Brondel

    Laurent Brondel Supporting Member

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    I put JJ's 6V6's on my '77 Princeton, they have more headroom than any other 6V6, so if you want your Princeton to stay clean a little louder (with the right speaker), this is a great choice. They sound more toward 6L6's. For safest and best sounding results it's probably best to check the bias…
     
  6. Blue Strat

    Blue Strat Member

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    Interesting, since the power supply and phase inverter seem to be the weak links regarding headroom in a PR.
     
  7. Laurent Brondel

    Laurent Brondel Supporting Member

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    The increased headroom is marginal, but it's there. JJ's also have a bit more top and low end.
     
  8. swiveltung

    swiveltung Member

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    I'm not sure the PI is an issue for greater headroom. I have a Princeton reverb I made 6L6 and Super reverb transformers. It is super loud and clean. I didn't do the "usual " PI mods though, although I did up the Filters a bit. Even playing outdoor gigs int he summer, I cant use that amp over about 3.5 on the volume pot!
     

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