Need a little help with a 61 Deluxe -

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by puddlian, Jun 1, 2005.

  1. puddlian

    puddlian Member

    Messages:
    24
    Joined:
    Jan 11, 2004
    I'll try to make the story short. I bought this deluxe for cheap a while back - non original trannies, yet the output tranny is "vintage". I had a tech mod this amp to run 6L6's. Sounds great but is now far to loud for my needs. So I want to put 6V6's back in. I went to rebias for a couple of JJ's (a bias pot has been added on the inside) but the sweep won't let me get anywhere near where I need to be - they start running way too hot!

    Soooooooooooo...
    What do YOU need to know so I can put what I need in order to rebias for 6V6's. The Power Tranny is a newer Mercury Magnetics FDRP-20 (Deluxe Reverb Power) and he also added a choke (022699). I'm thinking all I need to change is the Adjustment Pot to a different value and????
    I'd ask the guy who did the mod but unfortunately he passed away earlier this year.

    I'd love to do it myself , I have good soldering skills and the utmost respect for the amp's voltages, but I still don't want to fry myself.

    Thanks for any info -
     
  2. RussB

    RussB low rent hobbyist Silver Supporting Member

    Messages:
    11,040
    Joined:
    Jul 3, 2004
    Location:
    CT
    What's the plate voltage and current draw with the 6L6's and with the 6V6's?
     
  3. puddlian

    puddlian Member

    Messages:
    24
    Joined:
    Jan 11, 2004
    I must have been smokin' crack when I tried this before - they aren't running hot, I can't get them biased high enough.

    with 5881's - plate is 440 and bias is 23ma (that is what the tech set it at)

    with 6V6's - plate is 455 and the highest I can get the bias on my Marconi's or my JJ's is 8 or 9ma. So that is running very cold yes??? What do I need to do to get them up to where they need to be (bias calc says 18ma is that correct??)

    thanks!
     
  4. TheAmpNerd

    TheAmpNerd Member

    Messages:
    1,062
    Joined:
    Sep 23, 2004
    Location:
    Tejas
    How does it sound at the hottest setting?
     
  5. fullerplast

    fullerplast Senior Member

    Messages:
    6,792
    Joined:
    May 5, 2003
    Look at your bias pot. On a typical Fender one side will be connected to a diode and filter cap, the other side will have a resistor going to ground. You need to reduce the size of that fixed resistor so that you can get the bias voltage "less negative" and increase the bias current. If it is something like 27K, try a 15K. That should get you close. Try to get a value that gives you room on the pot to go either direction from your nominal bias setting.
     
  6. puddlian

    puddlian Member

    Messages:
    24
    Joined:
    Jan 11, 2004
    This is what I got

    [​IMG]

    It's a 10K resistor - what should I change it to? thanks!
     
  7. fullerplast

    fullerplast Senior Member

    Messages:
    6,792
    Joined:
    May 5, 2003
    Change the 10K resistor connected to the bias pot to either a 4.7K or 5.1K. That should get you in the range you want. Before you make any changes though, make sure you've checked the full range of the bias pot in both directions.
     

Share This Page