Switching between 6L6s and 6V6s... rectifier??

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by GenoBluzGtr, Sep 20, 2006.

  1. GenoBluzGtr

    GenoBluzGtr Supporting Member

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    I took delivery of a SDG 5E3 Proluxe today. The OT is beefed up to handle both types of tubes. It also has adjustable bias.

    Sounds great with the set of NOS tubes I put in (Jan Philips 6L6WGBs, RCA 12AX7, Mullard 4024) and Ruby 5AR4 rectifier.

    I set the bias at about 33-35 mA for that combo.

    I want to try 6V6s, but worry that the 5AR4 isn't right and don't want to risk any damage. Which Recitifier should I get for the smaller power tubes?

    Also, it seems to sound better with the 12AX7 in the preamp slot and the 4024 (12AT7) in the PI. That's backwards from the stock 5E3 config, but it sound's better and even cleaner to my ears than the other way around. Is it possible that the PI can induce more distortion than the preamp? I didn't get to crank it, but did run it up to about 5-6.
     
  2. Blue Strat

    Blue Strat Member

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    Hey Geno:
    It's mostly about plate voltage. Without knowing your plate voltage with the 5AR4 (and 6V6s installed) it's impossible to answer your question.

    If you bought the amp new, ask the builder. It's probably safe to ask him even if you didn't buy it new.

    Short of that, using a volt meter on pin 3 of the power tubes will answer the question.

    6V6s should generally be run at plate voltages lower than 430V.

    A 5R4 or 5V4 rectifier is almost certain to be safe.
     
  3. GenoBluzGtr

    GenoBluzGtr Supporting Member

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    I have the bias rite with the plate voltage mod... will that suffice to tell me, without having to use a probe in the "guts"?

    If I read your post right, I should install the 6V6s with the 5AR4, bias them properly (22-25 mA, right??) and read the plate voltage with the Bias Rite? If it's less than 430V, I should be fine, then?
     
  4. Blue Strat

    Blue Strat Member

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    Yes to all. So this amp has adjustable bias? Excellent! 5E3s are cathode biased.
     
  5. GenoBluzGtr

    GenoBluzGtr Supporting Member

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    Yeah, Steve Gupta (SDG) makes a standard 5E3, but also has options like the upgraded OT and adding Adjustable bias (to facilitate better use of the beefy OT with 6L6s). According to his website... http://www.sdgvintage.com/sdgvintage/amplifiers_vintage_Tube.asp ... this is a 5E3, except for three changes... OT, Adj Bias, and a Standby Switch.

    I'm not sure if anything in the circuit is changed other than adding a pot to the bias circuit, but he did say in an email that by using the adjustable bias, the amp has more clean power than a standard 5E3 (and not just becuase you are using different power tubes, but somehow just the fact that it has the pot makes it cleaner/with more oomph).
     
  6. Blue Strat

    Blue Strat Member

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    I'm guessing that he's using fixed/adjustable (sounds like an oxymoron, but it isn't) biasing which does give more power than cathode biasing.
     

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